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Frameworks, Terminology and Definitions Used for the Classification of Voice Disorders: A Scoping Review

  • Christopher L. Payten
    Correspondence
    Address correspondence and reprint requests to Christopher L Payten, Speech Pathology Department, Gold Coast University Hospital, 1 Hospital Boulevard, Southport, Queensland 4215, Australia.
    Affiliations
    Department of Speech Pathology and Audiology, Gold Coast Health, Gold Coast University Hospital, Southport, Queensland, Australia

    Faculty of Medicine and Health, Sydney School of Health Sciences, Discipline of Speech Pathology, University of Sydney, Camperdown, New South Wales, Australia
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  • Greg Chiapello
    Affiliations
    Department of Speech Pathology and Audiology, Gold Coast Health, Gold Coast University Hospital, Southport, Queensland, Australia
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  • Kelly A. Weir
    Affiliations
    Department of Allied Health Research, Gold Coast Health, Gold Coast University Hospital, Southport, Queensland, Australia

    Menzies Health Institute Queensland, School of Health Sciences, Griffith University, Gold Coast Campus, Southport, Queensland, Australia
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  • Catherine J. Madill
    Affiliations
    Faculty of Medicine and Health, Sydney School of Health Sciences, Discipline of Speech Pathology, University of Sydney, Camperdown, New South Wales, Australia
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Open AccessPublished:March 19, 2022DOI:https://doi.org/10.1016/j.jvoice.2022.02.009

      Summary

      Background

      A challenge for clinicians and researchers in laryngology is a lack of international consensus for an agreed framework to classify homogenous groups of voice disorders. Consistency in terminology and agreement in how conditions are classified will provide greater clarity for clinicians and researchers.

      Objective

      This scoping review aimed to examine the published literature on frameworks, terminology, and criteria for the classification of voice disorders.

      Design

      Seven online databases (MEDLINE, Embase, CINAHL, PsycInfo, Scopus, Cochrane Collaboration, Web of Science) and grey literature sources were searched. Studies published from 1940 to 2021 were included if they provided a descriptive detail of a classification framework structure and described the methodological approaches to determine classification. A narrative synthesis of the main concepts including terminology, classification criteria, grouping of conditions, critical appraisal items and gaps in research was undertaken.

      Results

      A total of 2,675 publications were screened. Twenty sources met inclusion criteria, including published articles and grey literature. Thirty-five classification groups and over 150 sub-groups were described. The classification group labels, and criteria for inclusion of conditions varied across the frameworks. Several key themes in terminology and criteria useful for classification are discussed, and a core set of suggested terms and definitions are presented.

      Conclusions

      The quality of research on classification frameworks for voice disorders is low and not one system encompasses all voice disorders across the whole spectrum. Continued high quality research using consensus methodology and inter-rater reliability scores is recommended to develop and test an internationally agreed classification framework for voice disorders.

      Key Words

      INTRODUCTION

      A reliable voice is an essential component of everyday communication.
      • Zhang Z
      Mechanics of human voice production and control.
      The voice can become disordered when the quality, pitch, loudness, flexibility and vocal effort are perceived to be different from others of a similar age, gender or cultural group.
      • Merrill RM
      • Roy N
      • Lowe J
      Voice-related symptoms and their effects on quality of life.
      An estimated 1.7% of the general population report vocal symptoms each year, with an increasing number seeking medical referrals for their symptoms.
      • Benninger MS
      • Holy CE
      • Bryson PC
      • et al.
      Prevalence and occupation of patients presenting with dysphonia in the United States.
      Dysphonia may be a symptom of a serious medical condition including neurological impairment and head/neck cancer, requiring time-sensitive medical diagnosis and management.
      • Stachler RJ
      • Francis DO
      • Schwartz SR
      • et al.
      Clinical practice guideline: hoarseness (Dysphonia) (Update).
      However, 40% to 60% of patients referred for voice assessment do not have any organic structural or neurological pathophysiology, with the vocal disorder resulting from other non-organic causes.
      • Roy N
      Functional dysphonia.
      Cost-effective treatment planning and prevention of symptom decline requires early multi-disciplinary assessment and accurate diagnosis.
      • Cohen SM
      • Jaewhan K
      • Roy N
      • et al.
      Delayed otolaryngology referral for voice disorders increases health care costs.
      The term “voice disorder” embodies many different conditions with signs and symptoms that can present in isolation or combination with each other.
      • Stachler RJ
      • Francis DO
      • Schwartz SR
      • et al.
      Clinical practice guideline: hoarseness (Dysphonia) (Update).
      As voice production involves the complex synergy of multiple physiological, biological, and psychosocial sub-systems, aetiology of the disorder can often be multifactorial. The process of classifying the cause of vocal decline, beyond identifying visible or organic laryngeal pathophysiology, is complex, and requires the expertise of multiple professionals.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      The multidisciplinary team contributing to the diagnosis of a voice disorder includes a combination of Otolaryngologists (Ear, Nose and Throat, ENT), Speech-Language Pathologists (SLP), voice scientists, psychologists, singing teachers and vocal coaches. Each professional will focus on a different level of the vocal symptoms to classify the vocal complaint. For example, ENTs may describe a voice disorder based on presence or absence of visually observed pathophysiology, whereas SLPs may describe voice disorders using subjective auditory perceptual judgements. Consequently, each professional may use their own medical jargon to describe similar voice symptoms or presentations. Clinicians will frequently use broad classification terms (eg, nonspecific dysphonia, chronic laryngitis, functional dysphonia, or non-organic dysphonia) to define homogenous groups of voice disorders where there is no distinct criteria to determine a specific diagnosis. Conversely, specific diagnostic terminology may be consistently used across professionals where there is visible laryngeal pathophysiology, regardless of the aetiology (eg, vocal fold nodules, vocal fold polyp, vocal fold paralysis). However, for many patients, there may be no single objectively identifiable cause for their vocal symptoms, and more than one condition may be contributing to multiple diagnoses and/or descriptors.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      Consequently, terminology for similar groups of voice disorders in the literature is often used interchangeably and without clear definition, specifically when the diagnostic nomenclature for observed organic pathology is not well defined or fully understood.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Roy N
      • Barkmeier-Kraemer J
      • Eadie T
      • et al.
      Evidence-based clinical voice assessment: a systematic review.
      Consistent classification terminology is important when diagnostic criteria for specific diseases are not available or are not considered useful for making a diagnosis. Clinicians frequently rely on classification criteria to inform their diagnostic impression, or to plan and communicate effective treatment recommendations.
      • Yazici H
      Diagnostic versus classification criteria: a continuum.
      Therefore, consistency in the terminology and criteria for classification of homogenous groups of voice disorders is needed to provide greater clarity for clinicians when communicating assessment findings and treatment outcomes.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      Additionally, clearly defined terminology and classification criteria will better inform the design of future studies that aim to measure the diagnostic value of the assessment process and test measures for this population.
      • Roy N
      • Barkmeier-Kraemer J
      • Eadie T
      • et al.
      Evidence-based clinical voice assessment: a systematic review.
      A useful classification system is one which is reliable and valid, and typically developed using one of two approaches.
      • Buchbinder R
      • Goel V
      • Bombardier C
      • et al.
      Classification systems of soft tissue disorders of the neck and upper limb: do they satisfy methodological guidelines?.
      The statistical approach uses statistical procedures to group patients with similar characteristics to demonstrate that the different groups do not have overlapping attributes. The judgment approach may rely on three forms of judgment: i) traditional custom, where the developer identifies the most important variables represented in the literature, ii) conventional wisdom, where the developer relies on common unpublished beliefs or clinician consensus to decide which variables should be included, and iii) personal experience. When using classification systems as a diagnostic tool, it is important to consider the clinical utility of the system and whether it provides a reliable description of the underlying disorders.
      • Buchbinder R
      • Goel V
      • Bombardier C
      • et al.
      Classification systems of soft tissue disorders of the neck and upper limb: do they satisfy methodological guidelines?.
      Review Objectives
      The primary objective of this review was to systematically examine the published literature to identify and evaluate the existing classification frameworks for voice disorders. We sought to examine themes in the different terminology used; describe the types of diagnoses and their diagnostic criteria (signs, symptoms, test results) that fit within each of the classification groups; and describe the types of clinical assessments used to determine classification. Additionally, we aimed to critically appraise studies that describe classification frameworks for voice disorders according to published methodological criteria
      • Buchbinder R
      • Goel V
      • Bombardier C
      • et al.
      Classification systems of soft tissue disorders of the neck and upper limb: do they satisfy methodological guidelines?.
      in order to recommend a core set of voice disorder classification groups and classification terms with corresponding criteria. This work will provide clarity for clinicians when classifying voice disorders that share similar diagnostic features to inform future research in assessment, classification, and treatment of these conditions.
      Review questions
      • 1.
        What frameworks, terminology and definitions for the classification of voice disorders are described in the literature?
      • 2.
        What clinical criteria exist within these frameworks to guide clinicians in the classification of voice disorders?
      • 3.
        Do the existing classification frameworks satisfy methodological guidelines for the development of classification systems?
      Sub-questions
      • 1.
        What specific conditions or diagnoses are described within the classification groups?
      • 2.
        What clinical assessments and case history information are described to guide the classification of voice disorders?

      METHODS

      Protocol registration

      The scoping review protocol was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analysis Protocols for Scoping Reviews (PRISMA-ScR)
      • Tricco AC
      • Lillies E
      • Zarin W
      • et al.
      PRISMA extension for scoping reviews (PRISMA-ScR): checklist and explanation.
      and the Joanna Briggs Institute (JBI) methodology for scoping reviews.
      • Peters MDJ GC
      • McInerney P
      • Baldini Soares C
      • et al.
      Chapter 11: scoping reviews.
      The final protocol was peer-reviewed and registered prospectively with the JBI systematic review register and published in the JBI evidence synthesis journal.
      • Payten CL
      • Chiapello G
      • Weir KA
      • et al.
      Terminology and frameworks used for the classification of voice disorders: a scoping review protocol.

      Information sources

      The following bibliographic databases were searched from 1940 to October 2021: MEDLINE (Ovid), Embase (Elsevier), CINAHL (EBSCOhost), PsycInfo (Ovid), Scopus (Elsevier), Cochrane Database of Systematic Reviews (Cochrane Library), and Web of Science (Clarivate analytics). Grey literature searches were also conducted through Google, Google Scholar, ClinicalTrials.gov, Cochrane Central Register of Controlled Trials (CENTRAL) and ProQuest Dissertations and Theses. In addition, grey literature searches included Speech-Language Pathology and ENT peak international bodies including Speech Pathology Australia (SPA), The Royal College of Speech and Language Therapists (RCSLT), The American Speech Language Hearing Association (ASHA), Australasian Society of Otolaryngology Head and Neck Surgery (ASOHNS), American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) and European Laryngological Society (ELS).

      Search strategy

      A three-step search strategy was used to identify relevant sources for the review. An initial search through PubMed, textbooks, international websites, and key review papers included the broad classification terms (organic voice disorder, functional voice disorder, psychogenic voice disorder). Key terms were then determined through discussion between two authors (CP, CM) and refined using key concepts addressing classification. The search strategy was reviewed by a senior medical librarian at the University of Sydney. The final search strategy for MEDLINE can be found in the appendix. Searches were modified for each database.
      The comprehensive search of all databases was conducted by the first author (CP) and a senior medical librarian at Gold Coast University Hospital with expertise in systematic review searching, on July 2, 2020. The first author conducted a final search to include new articles published to 14 October 2021. The search results were exported to EndNote X8 and the duplicates removed by the first author (CP) using the Bramer method.
      • Bramer WM
      • Giustini D
      • de Jonge GB
      • et al.
      De-duplication of database search results for systematic reviews in EndNote.
      In the final step of the search strategy, reference lists of all studies identified for full text review were examined for additional relevant sources not found during the bibliographic database search.

      Eligibility criteria

      Studies were included if they described a named classification framework for voice disorders. There was no age limit for participants in included studies because the same terminology is used for adults and children with voice disorders. Detailed inclusion and exclusion are described in Table 1. The year 1940 was selected because voice disorders of functional origin were first described around this time, and the aim of this review was to capture as a wide a range of the literature as possible. Disorders of cough and laryngeal airway (ie, inducible laryngeal obstruction, paradoxical vocal fold movement) were not included in this review.
      TABLE 1Inclusion/Exclusion Criteria
      InclusionExclusion
      PopulationParticipants (children or adult) diagnosed with a voice disorder using any diagnostic criteria.

      Quantitative, qualitative, and mixed methods studies; systematic reviews; reports; and grey literature that aim to evaluate patients with a voice disorder and including:

      A) The development or description of a voice disorder classification framework and/or classification criteria (ie, groups of conditions).and

      B) A description of defined criteria used to describe one or more voice disorder classification group(s)/framework.
      Studies including animal models.
      ConceptDescription of voice disorder classification or criteria or specific voice disorder diagnoses/criteria.

      Well-defined methodological approaches to determine a set of diagnostic criteria (eg, a consensus approach based on expert opinion; statistical modelling; systematic literature reviews; methods considering multiple diagnostic tests).
      Classification systems for laryngeal airway diagnoses (ie, paradoxical vocal fold movement, inducible laryngeal obstruction), chronic cough, alaryngeal speech, elective mutism, or resonance disorders.
      ContextGeographical and clinical contexts (specifically the treating professions) where a classification or diagnosis of voice disorder has been employed

      Articles published in English Language

      Articles published from 1940 to October 2021
      Studies in languages other than English.

      Selection of sources of evidence

      After deduplication, references were uploaded to Covidence for screening.

      Covidence Systematic Review Software, V.H.I., Melbourne, Australia. Available at: www.covidence.org.

      Titles and abstracts were independently screened for eligibility by two authors (CP, GC). When screening was unable to determine if the title or abstract met inclusion criteria, the article was selected for full text review. Full text reviewing was conducted independently by the same authors (CP, GC) and any conflicts were resolved through discussion. When agreement on inclusion could not be met, consensus was achieved using a third reviewer (CM).
      A purposive data extraction form was developed through discussion with the research team to determine the variables to extract. Two reviewers (CP, GC) independently read and extracted the data, whilst continually discussing the results and clarifying questions during the extraction process. Extracted data included specific details about the study population (authors, year of publication, participant details); concept (classification frameworks, terminology used, classification criteria used or tested, clinical assessment data used for classification, level of evidence); context (country of study, author profession).

      Data extraction and synthesis

      All classification frameworks and the disorders listed were placed into a table (supplementary file). The frameworks were described in terms of overall structure and themes in terminology and classification criteria. We define structure as the distinct conceptualisation and differentiation of which disorders were included in the system and what criteria was used to group conditions within the framework. We attempted to reduce bias in our reporting of the extracted data by using a standardised set of terminology in this review. A glossary of terms can be found in Table 2. To address the heterogenous semantic labels for the same or similar disorders described across the various frameworks, during the review process we grouped each disorder into one of three analysis domains and applied a group label (hyperfunction-muscle tension, psychosocial, organic) to facilitate subsequent appraisal. After reviewing all the papers and extracting the data both reviewers (CP, GC) identified the same three broad categories prior to any discussion. The analysis domain labels were selected from common terms used in the literature, and terms we concluded were the most descriptive of the entire group of disorders contained within each analysis domain. This allowed a comparison of the terminology used by authors for similar clinical entities across frameworks.
      TABLE 2Glossary of Terms Used in the Reporting of This Review
      Classification frameworkA structured framework consisting of single or multiple groups of conditions.
      Classification groupAn overarching group where authors have described homogenous cohorts of voice disorders or sub-groups of voice disorders.
      Multi-axis frameworkA classification framework where authors include more than one classification group of voice disorders.
      Single-axis frameworkA classification framework where authors describe a single classification group.
      Sub-groupA sub-group of voice disorders contained within a single classification group.
      Groups of conditionsGroups of voice disorders listed within a sub-group, that is, hypo-functional neurological conditions, with a neurological subgroup.
      Disorder/diagnosis/conditionA specific voice disorder contained within a classification group or within a subgroup
      Analysis domainA temporary domain group label used by the authors of this scoping review to assist with data synthesis and reporting of the terminology.
      To explore the classification criteria described by authors in their frameworks, we extracted data including details of the assessment tools described, assessment protocols, and clinical observations described by the authors. This data was included in the data extraction table (supplementary file).

      Evaluation of study quality and framework development methodology

      The quality of all eligible studies was assessed using relevant subsections from the JBI critical appraisal tools.
      • Peters MDJ GC
      • McInerney P
      • Baldini Soares C
      • et al.
      Chapter 11: scoping reviews.
      Each study was blindly appraised by two independent reviewers (CP, GC), ratings were compared and discussed, and final consensus ratings determined. To evaluate how the classification frameworks satisfy recommended guidelines we used a previously published critical appraisal and risk-of-bias tool validated for the appraisal of classification systems, to evaluate a sub-set of articles (n = 7) which described multi-axis frameworks.
      • Buchbinder R
      • Goel V
      • Bombardier C
      • et al.
      Classification systems of soft tissue disorders of the neck and upper limb: do they satisfy methodological guidelines?.
      The same two reviewers (CP, GC) critically appraised and scored each study in this sub-set blindly according to seven domains: appropriateness for purpose, content validity, face validity, feasibility, construct validity, reliability, and generalizability. An allocated weighted score was agreed for each article by the same reviewers through a consensus.

      RESULTS

      Identified studies

      The database search found a total of 2,675 publications for title and abstract review, documented in the PRISMA flow diagram (Figure 1). Independent review was conducted on 113 full-text articles and nine sources of grey literature (book chapters). A total of 20 sources met inclusion criteria and were selected for data extraction.

      Study characteristics

      Tables 3 and 4 outline the voice disorder classification labels from the 20 selected articles. A complete summary of the extracted data from each source is provided in the supplementary file. The earliest paper was published in 1960, eight were published between 1960 and 2000, and the remaining 11 were published between 2000 and 2020. Most of the studies originated from the United States (n = 10), followed by Canada (n = 2), and United Kingdom (n = 2). Authors from Australia, Belgium, Spain, Serbia, Netherlands, and Germany each contributed one source of evidence included in this review. The predominant author profession was ENT (n = 8), followed by combined ENT and SLP (n = 5), then SLP and speech scientists (n = 2), and SLP and psychologists (n = 2). Seven of the 20 sources described multi-axis frameworks, and thirteen detailed a single axis framework.
      TABLE 3aMulti-axis Frameworks: Classification Group Terminology and Included Subgroups/Conditions Where Classification is by Aetiology of the Voice Disorder
      Morrison et al, 1986.
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.


      Canada, ENT/SLP/Psych
      Baker et al, 2007.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.


      Australia, SLP/ENT
      Functional (psychological) Dysphonia (FD).Functional Psychogenic Voice Disorder (PVD).
      Hyper adducting ventricular band dysphonia.

      FD with bowed vocal folds.

      FD with hyperadduction (hysterical aphonia).

      FD with non-specific features.
      PVD Type 1 (aphonia).

      PVD Type 2 (dysphonia).

      PVD Type 3 (Psychogenic spasmodic dysphonia).

      PVD Type 4 (Puberphonia/mutational falsetto).
      Muscular Tension Dysphonia (MTD).Functional Muscle Tension Voice Disorder (MTVD).
      MTD 1 (posterior chink).

      MTD 2a (vocal nodules).

      MTD 2B (chronic laryngitis).

      MTD 2C (polypoidal degeneration).
      Type 1 (no secondary pathology).

      Type 2a (secondary pathology).

      Type 2b (with secondary pathology).

      Type 2c (with secondary pathology).
      Spasmodic dysphonia.Organic Voice Disorder (OVD)
      Voice disorder which relates to both organic and functional disturbances.Type 1 (mass lesions of tissue changes).

      Type 2 (laryngeal trauma).

      Type 3 (neurological LMN).

      Type 4 (neurological Adductor/abductor spasmodic dysphonia).

      Type 5 (neurological UMN with dysarthrophonia).
      Abbreviations: ENT, Ear Nose and Throat Surgeon; LMN, lower motor neurone; Psych, Psychiatrist; SLP, Speech Language Pathologist; UMN, upper motor neurone; VF, vocal fold.

      Data synthesis

      Comparisons of classification framework structure

      The multi-axis frameworks all included a comprehensive structure with a range of disorders represented and mostly grouped according to non-organic and organic characteristics (Table 3a, Table 3b and Table 3c). Four of the seven authors divided their framework into three classification groups.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      Whereas Miltutinovic included two,
      • Milutinovic Z
      Classification of voice pathology.
      Bradley four,
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      and Verdolini and colleagues of the American Speech-Language-Hearing Association Special Interest Division 3 (ASHA SIG-3) classification manual for voice disorders-I described nine classification groups.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      There were similarities in the characteristics of voice disorders represented across the frameworks. However differences in the terminology used to label the classification groups, subgroups, and conditions represented within them. Furthermore, patterns in the methods used by authors in how they chose to group conditions within the multi-axis frameworks existed. Two authors grouped conditions according to the primary aetiology and the observed features of the voice disorder (Table 3a).
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      Several authors grouped and labelled conditions based on the presence or absence of organic pathology (Table 3b).
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      • Milutinovic Z
      Classification of voice pathology.
      Whereas two authors classified conditions based on the location and characteristics of the primary aetiology contributing to the voice disorder, for example, inflammatory conditions, structural changes, neuromuscular and muscle tension imbalances (Table 3c).
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      TABLE 3bMulti-axis Frameworks: Classification Group Terminology and Included Subgroups/Conditions Where Classification is by the Presence or Absence of Organic Pathology
      Damste, 1973.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.


      Netherlands, SLP
      Milutinovic, 1996.
      • Milutinovic Z
      Classification of voice pathology.


      Serbia, ENT
      Rosen and Murray, 2000.
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.


      USA, ENT/SLP
      Functional dysphonia.Functional voice disorder.Nonorganic voice disorder.
      Psychogenic aphonia.

      Psychogenic dysphonia.

      Dysphonia spastica.

      Habitual dysphonia.

      Habitual dysfunction during/after  mutation.
      Phononeurosis

      (dysphonia arising from psychogenic superimposition).

      Phonoponosis

      (dysphonia arising from disharmonic activity).
      Muscle Tension Aphonia (MTA)

      (psychogenic voice disorder).

      Primary muscle tension dysphonia  (MTD).
      Secondary organic dysphonia (consequences of vocal strain).Organic voice disorder.Organic voice disorder.
      Simple laryngitis.

      Chronic nodular laryngitis.

      Vocal fold oedema.

      Polyps.

      Chronic hypertrophic

       laryngitis (contact ulcer,  leucoplakia).

      Disorders of feedback mechanisms of voice control.

      Congenital disorders.

      Inflammatory processes.

      Chronic mucosal irritation.

      Respiratory.

      Hormonal disorders.





      Myopathy of the laryngeal muscles.

      Disorders of the nervous system.

      Syndrome of excessively

       inappropriate pitch (IVP).

      Trauma.

      Benign growths.

      Malignant tumours.
      Epithelium changes.

      Lesions of the lamina propria.

      Arytenoid disorders.

      Other.
      Primary organic dysphoniaMovement disorders of the larynx.
      Congenital malformation.

      Paralysis.

      Changes by endocrine disorder.

      Specific infections.

      Trauma.

      Tumours.
      VF paralysis and other pathological conditions of the CA joint.

      VF paresis/atrophy.

      Other laryngeal movement  disorders.
      Abbreviations: CA, crico-arytenoid; ENT, Ear Nose and Throat Surgeon; SLP, Speech Language Pathologist; USA, United States of America; VF, vocal fold.
      TABLE 3cMulti-axis Frameworks: Classification Group Terminology and Included Subgroups/Conditions Where Classification is by the Location and Characteristics of Aetiology
      Verdolini et al, 2005.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).


      USA, SLP/ENT
      Bradley 2010.
      • Bradley PJ
      • et al.
      Voice disorders: classification.


      UK, ENT
      Inflammatory conditions of the larynx.Inflammation.
      Cricoarytenoid and cricothyroid arthritis.

      Acute laryngitis.

      Laryngopharyngeal reflux.

      Chemical sensitivity or irritable larynx syndrome.
      Infective.

      (Primary laryngeal: viral/bacterial, fungal, secondary:  pulmonary/rhinosinusitis).

      Non infective.

      (LPR, allergy, trauma/irritation, autoimmune, nonspecific).

      Systemic conditions affecting voice.
      Endocrine.

      Immunologic.

      Musculoskeletal conditions affecting voice.
      Non laryngeal aerodigestive disorders affecting voice.
      Respiratory diseases affecting voice.

      Digastric.

      Infectious diseases of the aerodigestive tract.

      Mycotic (fungal) infections.
      Structural pathologies of the larynx.Neoplastic/Structural.
      Malignant laryngeal lesions.

      Epithelial and lamina propria abnormalities of the  vocal fold.

      Vascular anomalies of the vocal fold.

      Congenital and maturational changes affecting the  vocal fold.
      Benign deficits/tethering.

      Microvascular lesions.

      Endocrinological.

      Inflammatory mass.

      Laryngeal framework trauma.

      Neoplasms.

      Laryngoceles.

      Mixed/reactive.

      Malignant/premalignant.

      Minor salivary gland.
      Trauma or injury of the larynx.
      Internal laryngeal trauma.

      External laryngeal trauma.
      Neurological disorders affecting voice.Neuromuscular.
      Peripheral nervous system pathology.

      Movement disorders affecting the larynx.

      Central nervous system disturbance.
      Hypo-functional.

      Hyper-functional.

      Mixed or variable hypo-/hyper-functional.

      Control/coordination.
      Other disorders affecting voice.Muscle tension imbalance.
      Muscle tension dysphonia (Primary).

      Muscle tension/adaptive dysphonia (secondary).

      Ventricular dysphonia.

      Paradoxical vocal fold movement disorder.
      Primary muscle tension imbalance.

      (Vocal demand/strain/psychogenic/puberphonia).

      Secondary muscle tension imbalance.

      (Dysphonia in the presence of an underlying organic  condition).
      Psychiatric and psychological disorders affecting voice.
      Somatoform disorders.

      Factitious disorder.

      Selective mutism.

      Anxiety.

      Mood disorders.

      Gender identity disorder.

      Psychogenic polydipsia.

      Psychogenic tremor-like voice fluctuations.
      Voice disorders: undiagnosed or not otherwise specified.
      Abbreviations: ENT, Ear Nose and Throat Surgeon; LPR, laryngo pharyngeal reflux; SLP, Speech Language Pathologist; UK, United Kingdom; USA, United States of America.
      All but three of the thirteen single-axis frameworks described conditions of non-organic characteristics under a single classification group (Table 4a).
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      • Hillman RE
      • Holmberg EB
      • Perkell JS
      • et al.
      Objective assessment of vocal hyperfunction: an experimental framework and initial results.
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      • Van Houtte E
      • Van Lierde K
      • Claeys S
      Pathophysiology and treatment of muscle tension dysphonia: a review of the current knowledge.
      • Spencer ML
      Muscle tension dysphonia: a rationale for symptomatic subtypes, expedited treatment, and increased therapy compliance.
      • Fernández S
      • Garaycochea O
      • Martinez-Arellano A
      • et al.
      Does more compression mean more pressure? A new classification for muscle tension dysphonia.
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      • Hacki T
      • Moerman M
      • Rubin JS
      Malregulative’ rather than ‘Functional’ dysphonia: a new etiological terminology framework for phonation disorders—a position paper by the Union of European Phoniatricians (UEP).
      Arnold included a range of disorders of both non-organic and organic aetiologies grouped together under a single group label ventricular dysphonia (Table 4a).
      • Arnold GE
      • Pinto S
      Ventricular dysphonia: new interpretation of an old observation.
      Whereas two articles by Rosen and colleagues described frameworks for specific disorders, namely vocal fold motion impairment resulting from neurogenic, mechanical and pathological causes and benign vocal fold lesions (BVFL) (Table 4b).
      • Rosen CA
      • Mau T
      • Hess M
      • et al.
      Nomenclature proposal to describe vocal fold motion impairment.
      ,
      • Rosen CA
      • Gartner-Schmidt J
      • Hathaway B
      • et al.
      A nomenclature paradigm for benign midmembranous vocal fold lesions.
      TABLE 4aSingle-axis Frameworks: Classification Group Terminology and Included Subgroups/Conditions. Conditions of Non-organic/Mixed Organic and Non-organic Aetiology
      Arnold and Pinto, 1960
      • Arnold GE
      • Pinto S
      Ventricular dysphonia: new interpretation of an old observation.
      USA

      ENT
      Aronson et al, 1966
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      USA

      SLP/Psych
      Koufman and Blalock, 1982
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      USA

      ENT
      Hillman et al, 1989
      • Hillman RE
      • Holmberg EB
      • Perkell JS
      • et al.
      Objective assessment of vocal hyperfunction: an experimental framework and initial results.
      Canada

      ENT/SLP/Psych
      Morrison and Rammage, 1993
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      Canada

      ENT/SLP
      Butcher et al, 2007
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      UK

      Psychol/SLP
      Van Houtte et al, 2011
      • Van Houtte E
      • Van Lierde K
      • Claeys S
      Pathophysiology and treatment of muscle tension dysphonia: a review of the current knowledge.
      Belgium

      ENT/SLP
      Spencer, 2015
      • Spencer ML
      Muscle tension dysphonia: a rationale for symptomatic subtypes, expedited treatment, and increased therapy compliance.
      USA

      ENT
      Hillman et al, 2020
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      USA

      SLP/SpSc
      Fernandez et al, 2020
      • Fernández S
      • Garaycochea O
      • Martinez-Arellano A
      • et al.
      Does more compression mean more pressure? A new classification for muscle tension dysphonia.
      Spain

      ENT
      Hacki et al, 2022
      • Hacki T
      • Moerman M
      • Rubin JS
      Malregulative’ rather than ‘Functional’ dysphonia: a new etiological terminology framework for phonation disorders—a position paper by the Union of European Phoniatricians (UEP).


      Europe

      ENT
      Ventricular Dysphonia (VD).Functional Dysphonia.Functional Dysphonia.Vocal Hyperfunction (VH).Muscle Misuse Voice Disorder.Psychogenic Voice Disorder.Muscle Tension Dysphonia (MTD).Muscle Tension Dysphonia (MTD)Vocal Hyperfunction (VH)Muscle Tension Dysphonia (MTD)Malregulative Dysphonia
      Habitual VD.

      Emotional VD.

      Paralytic VD.

      Cerebral VD.

      Cerebellar VD.

      Vicarious VD.
      Muteness.

      Continually whispered speech.

      Intermittently phonated

      whispered speech.

      Continually phonated speech.
      Hysterical aphonia/dysphonia.

      Habituated hoarseness.

      Falsetto.

      Voice abuse.

      Postoperative dysphonia.
      Adducted VH.

      Non adducted VH.
      Laryngeal isometric.

      Lateral hyper-adduction: glottis/supraglottis.

      Supraglottic A-P contraction.

      Conversion aphonia.

      Psychogenic bowing.

      Adolescent transitional dysphonia.
      Type 1: classical (hysterical) conversion.

      Type 2: cognitive behavioral conversion.

      Type 3: Habitual conversion.
      Primary MTD.

      Secondary MTD.
      Glottal fry.

      Excessively lowered speaking pitch.

      Register flipping.

      Functional aphonia.

      Post surgical functional dysphonia.

      Excessively pressed phonation.

      Puberphonia.

      “Primary” plica

      ventricularis.

      Functional hypophonia.
      Phonotraumatic VH.

      Non Phonotraumatic VH.
      Grade1 A-P compression.

      Grade2 A-P compression.

      Grade3 A-P compression.

      Grade1 Lat compression.

      Grade2 Lat compression.

      Grade3 Lat compression.
      No sub-groups included
      Abbreviations: A-P, anterior posterior; ENT, Ear Nose and Throat Surgeon; Lat, lateral; Psych, Psychiatrist; Psychol, Psychologist; SLP, Speech Language Pathologist; SpSc, Speech Scientist; UK, United Kingdom; USA, United States of America; VF, vocal fold. manuscript in press at the time of review.
      TABLE 4bSingle-axis Frameworks: Classification Group Terminology and Included Subgroups/Conditions. Conditions of Organic Aetiology
      Rosen et al, 2012
      • Rosen CA
      • Gartner-Schmidt J
      • Hathaway B
      • et al.
      A nomenclature paradigm for benign midmembranous vocal fold lesions.


      USA

      ENT
      Rosen et al, 2016
      • Rosen CA
      • Mau T
      • Hess M
      • et al.
      Nomenclature proposal to describe vocal fold motion impairment.


      USA

      ENT
      Benign Mid-membranous Vocal Fold Lesions (BVFL)Vocal Fold (VF) Motion Impairment
      VF nodules.

      VF polyp.

      VF cyst.

      Fibrous mass.

      Reactive VFL.

      Pseudocyst.

      Nonspecific VFL.
      VF immobility.

      VF hypomobility.

      VF paralysis.

      VF paresis.

      VF immobility/hypomobility associated with mechanical impairment

      of the CA joint.

      VF immobility/hypomobility related to laryngeal malignant disease.
      Abbreviations: CA, cricoarytenoid; ENT, Ear Nose and Throat Surgeon; USA, United States of America.

      Comparing classification group terminology and included conditions

      Thirty-five classification groups were described across the sources, and more than 150 subgroups or conditions. The most frequently used labels for the classification groups included: muscle tension, muscular tension,
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      ,
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      • Van Houtte E
      • Van Lierde K
      • Claeys S
      Pathophysiology and treatment of muscle tension dysphonia: a review of the current knowledge.
      • Spencer ML
      Muscle tension dysphonia: a rationale for symptomatic subtypes, expedited treatment, and increased therapy compliance.
      functional,
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      ,
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      • Milutinovic Z
      Classification of voice pathology.
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      psychogenic, psychological,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      and organic.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      • Milutinovic Z
      Classification of voice pathology.
      Despite the use of similar terminology, there were differences in how subgroups or conditions were placed under these labels, specifically where muscle tension and functional were concerned. For example, some authors included conditions pertaining to psychosocial and muscle tension characteristics under the classification group label functional (Table 3b and Table 4a),
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      ,
      • Milutinovic Z
      Classification of voice pathology.
      ,
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      whereas others placed these conditions under muscle tension (Table 3a and Table 4a).
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      ,
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      ,
      • Spencer ML
      Muscle tension dysphonia: a rationale for symptomatic subtypes, expedited treatment, and increased therapy compliance.
      Only three authors used the term functional exclusively to represent voice disorders of psychogenic aetiology.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      ,
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      In our comparison, we could not find an association across the sources to explain these differences, including the year of publication, country of author(s), or professional group.
      Classification of trauma induced mucosal changes (eg, vocal fold polyps, vocal fold nodules) was also a key difference across the frameworks. Most frameworks included mucosal changes as a subgroup under a muscle tension classification.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      In these frameworks’ authors used the prefix or suffix primary, to denote muscle tension with no laryngeal pathology, (ie, primary muscle tension dysphonia, primary muscle tension imbalance, muscle tension dysphonia-primary) or secondary to define a compensatory laryngeal muscle tension in response to laryngeal pathology.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Van Houtte E
      • Van Lierde K
      • Claeys S
      Pathophysiology and treatment of muscle tension dysphonia: a review of the current knowledge.
      Furthermore, the ASHA SIG-3 group advocate the term muscle tension/adaptive dysphonia (secondary) to reflect the compensatory maladaptation of laryngeal patterns in response to a primary organic cause.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      In support of this, Hillman and colleagues introduced a theoretical model of vocal hyperfunction and described this as “increased and less well-regulated laryngeal muscle tensions” [Hillman et al, 1989, p.374]. They report impaired muscle tensioning can result in varying risks for vocal fold collision forces and subsequent vocal fold trauma.
      • Hillman RE
      • Holmberg EB
      • Perkell JS
      • et al.
      Objective assessment of vocal hyperfunction: an experimental framework and initial results.
      On the other hand, according to this framework, increased stiffness of the vocal folds from maladaptive tensioning, in the absence of organic pathology, impairs glottic closure during phonation.
      • Hillman RE
      • Holmberg EB
      • Perkell JS
      • et al.
      Objective assessment of vocal hyperfunction: an experimental framework and initial results.
      The same authors updated their terminology to nonphonotraumatic vocal hyperfunction (NVH) and phonotraumatic vocal hyperfunction (PVH) in 2020.
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      Conversely, other authors appeared to exclude mucosal changes resulting from trauma from their respective non-organic classification groups. For example, Rosen described lesions of the epithelium, lamina propria and arytenoid, and Milutinovic grouped benign growths, under their organic voice disorder classification groups.
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      ,
      • Milutinovic Z
      Classification of voice pathology.
      Similarly, Damste placed these conditions into a group labelled secondary organic.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      With respect to voice disorders commonly referred to as organic in the literature, most frameworks included a broad list of conditions under a single classification group label (eg, organic, primary organic).
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      • Milutinovic Z
      Classification of voice pathology.
      However, both Bradley and the ASHA SIG-3 group described multiple classification groups, where conditions were classified according to their broad similarities in underlying aetiology.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      Examples of these classification group labels include structural, inflammatory conditions, trauma or injury, neuromuscular or movement disorders.

      Comparing classification definitions and criteria

      To facilitate charting and comparison of the classification criteria we allocated each classification group and/or subgroup to one of three broad analysis domains: hyperfunction-muscle tension, psychosocial, and organic. These provisional domain labels were selected based on the pattern of how the multi-axis frameworks are commonly structured, and terminology we felt broadly best described the conditions within each domain, as discussed in the methodology, section 2.6. Data extraction and charting of this information is captured in the supplementary file. The broad themes are discussed below.
      Hyperfunction–muscle tension analysis domain
      The most frequent definitions used for voice disorders placed in the hyperfunction-muscle tension analysis domain included: visible and palpable muscle tension in the larynx
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      ,
      • Milutinovic Z
      Classification of voice pathology.
      ,
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      ,
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      ,
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      ; malregulated, maladaptive, and inefficient laryngeal tensioning,
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Hillman RE
      • Holmberg EB
      • Perkell JS
      • et al.
      Objective assessment of vocal hyperfunction: an experimental framework and initial results.
      ,
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      ,
      • Hacki T
      • Moerman M
      • Rubin JS
      Malregulative’ rather than ‘Functional’ dysphonia: a new etiological terminology framework for phonation disorders—a position paper by the Union of European Phoniatricians (UEP).
      normal laryngeal condition/structure
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      ,
      • Arnold GE
      • Pinto S
      Ventricular dysphonia: new interpretation of an old observation.
      ; normal vocal fold morphology
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      ; absence of identifiable physical or neurological disease in the larynx
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Milutinovic Z
      Classification of voice pathology.
      ; and demonstrated patterns of vocal fold abuse.
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      The assorted frameworks further sub-divided these groups according to various criteria, as described below.
      Clinical assessment. Visible laryngeal tension of the intrinsic musculature observed with laryngoscopy was described by all authors as a defining feature of this classification group. Some further graded subgroups according to the degree of observed supraglottic/glottic constriction. Morrison described three subgroups including isometric, lateral and anterior-posterior glottic/supraglottic contraction.
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      Similarly, Fernandez defined sub-classes of Muscle Tension Dysphonia by the degree of supraglottic anterior-posterior (AP) constriction (AP1–AP3 compression).
      • Fernández S
      • Garaycochea O
      • Martinez-Arellano A
      • et al.
      Does more compression mean more pressure? A new classification for muscle tension dysphonia.
      However, supraglottic tension does not appear to be an exclusive clinical sign for these voice disorders. This is demonstrated in Arnold's model of ventricular dysphonia, defined by faulty participation of the ventricular folds arising from multiple aetiologies, including compensatory mechanism for neurogenic impairments, or altered laryngeal structure.
      • Arnold GE
      • Pinto S
      Ventricular dysphonia: new interpretation of an old observation.
      Hillman and Colleagues presented a range of aetiological factors they considered important for classification to their NVH and PVH groups of vocal hyperfunction.
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      These included vocal load, palpable extrinsic laryngeal tension with phonation, changes in sub-glottic air pressures and degree of collision forces of the vocal folds. Other authors have described similar features for their muscle tension classification groups further supporting them as unique to this group of disorders.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      Clinical features. In the frameworks where classification criteria were most clearly defined, specific history features including symptom onset, progression, and secondary symptoms were considered important when differentiating voice disorders of hyperfunction-muscle tension and those of psychosocial domains. Onset of the voice disorder in this group was frequently cited as gradual, long-standing, persistent, and fluctuating to vocal or emotional demands.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      ,
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      Furthermore, secondary symptoms of vocal fatigue, perceived vocal effort or strain, and pain on phonation were also described exclusively in the criteria of these voice disorders. A critical point emphasised by Baker for classification to their muscle tension voice disorder group is the individual's ability for voluntary control over vocal production, and noticeable improvement elicited through reflex activities (ie, yawning) or tasks designed to modify the technique of phonation.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      Psychosocial analysis domain
      Seven papers described independent classification groups that were placed into the psychosocial aetiology analysis domain (supplementary file); two sources were single-axis,
      • Aggarwal R
      • Ringold S
      • Khanna D
      • et al.
      Distinctions between diagnostic and classification criteria?.
      ,
      • Hunder GG
      • Arend WP
      • Bloch DA
      • et al.
      The American College of Rheumatology 1990 criteria for the classification of vasculitis: introduction.
      and five were from multi-axis frameworks.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      ,
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      ,
      • Milutinovic Z
      Classification of voice pathology.
      Additionally, five authors included subgroups and conditions which appeared to fit to this domain but were listed as part of a heterogenous classification group overlapping with other disorders.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      ,
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      ,
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      ,
      • Arnold GE
      • Pinto S
      Ventricular dysphonia: new interpretation of an old observation.
      Most authors defined this group as dysphonia or aphonia in the absence of laryngeal pathophysiology and in the presence of psychological or psychiatric disturbances. Classification criteria varied across the studies; however common themes were present.
      Clinical assessment. Several authors defined these conditions by various laryngeal postures as observed on laryngoscopy, similarly to the hyperfunction-muscle tension groups. For example, Arnold defined emotional ventricular dysphonia as ventricular fold approximation in response to stressful episodes.
      • Arnold GE
      • Pinto S
      Ventricular dysphonia: new interpretation of an old observation.
      Morrison defined Types 4 - 6 in his model by the vocal fold closure pattern or absence of glottic closure during phonation, in response to psychological or emotional conflict.
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      However, as previously discussed, these observations appeared to overlap with other disorders that fit with conditions in other classification groups.
      Auditory-perceptual assessment of vocal quality and amount of perceived voice frequently appeared in the descriptions for this group of voice disorders. Aronson and colleagues described patients diagnosed with hysterical/conversion dysphonia
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      and grouped them into subgroups of muteness, continually whispered speech, intermittently phonated whispered speech and continually phonated speech.
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      Others described specific perceptual features of the voice under this classification, including high-pitched, whispered vocal quality, and pitch locked.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      ,
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      However, the remaining sources described mixed or variable perceptual features in this group and reported similar vocal features in other classification groups of voice disorders.
      Clinical features. Butcher and colleagues stressed diagnosis should ideally include psychological evaluation and, in their framework, a psychogenic voice disorder should not be a diagnosis of exclusion. Classification under this model was according to how well patients met the criteria for a conversion of psychological stress into physical symptoms, as defined by the Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria.
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      Considering a slightly different aspect, the ASHA SIG-3 group categorised conditions in this classification group according to the various terms used in the DSM-IV, where they assert the voice characteristics are a secondary response to the primary cause, being any of the identified psychiatric or psychological conditions.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      In contrast to other frameworks, where a voice disorder is present and appears to have a psychogenic component but does not meet DSM-IV criteria for a psychiatric or psychological disorder, in the ASHA SIG-3 model it is categorised as Undiagnosed or not otherwise specified.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      Baker and colleagues described four types of psychogenic voice disorder in their Diagnostic Classification System for Voice Disorders (DCSVD).
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      In addition to the detailed summary of defining features of this classification group and each subgroup, they included stressful life events or experiences of trauma may co-occur with a sudden onset of vocal symptoms. However, the authors also assert that many patients may not always describe psychosocial experiences at the onset of symptoms.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      The number one defining feature for the psychogenic voice disorder classification group in Baker's framework is a loss of volitional control over the initiation and maintenance of normal voice without neurological or structural pathology.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      In agreement with this, many authors stated improved phonation in this group of patients is not easily influenced by vocal technique, despite normal laryngeal behaviors or a normally perceived voice observed during incidental vegetative tasks such as coughing or laughing.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      ,
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      Organic analysis domain. The nomenclature used to describe voice disorders we placed into the organic analysis domain for this review was sourced from 10 papers, of which 6 were multi-axis frameworks.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      • Milutinovic Z
      Classification of voice pathology.
      Overall, 21 classification groups were described and 94 subgroups or conditions (Tables 3 and 4). Many frameworks did not provide sufficient detail of the classification criteria for all subgroups/conditions within their frameworks (supplementary file). As such, we could only extract data from 68% of the sources for this domain. Most frameworks grouped conditions according to broad themes of underlying structural, mucosal or neurogenic pathophysiology. These range from three classification groups encompassing a range of conditions with shared features,
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      ,
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      to 12 separate classification groups.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      The themes for how these were organised across the frameworks are discussed below.
      Vocal fold pathology/inflammatory conditions were included by most authors using the same or similar terminology. Certain authors grouped these conditions into a single subgroup and further defined the specific conditions contained within the group. For example, Baker's mass lesions or tissue changes subgroup.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      Other authors split the same conditions across multiple classification groups, for example the ASHA SIG-3 structural pathologies and inflammatory conditions groups.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      Similarly, Bradley's model divided these conditions into inflammation (infective and non-infective) and structural/neoplastic.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      Laryngeal trauma was included in most frameworks as a separate condition under a single organic classification group, except Bradley and Rosen.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      ,
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      Rosen included trauma of the larynx within the organic voice disorder group,
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      and Bradley as part of the structural/neoplastic classification group.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      Both frameworks had the fewest number of classification groups, which may explain this decision.
      Neurological and neuromuscular conditions were clearly defined in most frameworks, with common themes in the grouping of these conditions. Bradley included four subgroups of conditions, under a single classification group defined by the patients’ presenting signs or symptoms of hypo- or hyper-muscular function.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      Similarly, the ASHA SIG-3 group divided a neurological conditions classification group into multiple subgroups defined by site of neurological injury or breakdown (CNS, PNS), and included a separate subgroup called movement disorders encompassing spasmodic dysphonia and essential laryngeal tremor amongst others.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      Baker described three subgroups of neurological conditions, under the classification group organic voice disorders, with subgroups for lower motor neurone conditions, upper motor neurone conditions, and a third group encompassing spasmodic dysphonia and essential laryngeal tremor.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      Voice disorders not included in the analysis domains
      Only one condition that was included in numerous frameworks did not match any of the descriptions of the three chosen analysis domains. Puberphonia/mutational dysphonia/adolescent transitional dysphonia was grouped under different classification groups across many of the frameworks. Bradley's model placed this condition in the primary muscle tension classification group
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      ; Baker, Spencer and Morrison described it in the psychosocial grouping
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      ,
      • Spencer ML
      Muscle tension dysphonia: a rationale for symptomatic subtypes, expedited treatment, and increased therapy compliance.
      ; and ASHA SIG-3 placed the condition in the structural pathology, congenital and maturational changes affecting voice classification group.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      However, Verdolini defines this condition as the “consistent use a of a high-pitched voice in a post-pubescent individual, usually male, without known organic cause” [Verdolini et al, 2005, p.83] often with secondary gains.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      It may therefore be argued that a more suitable category for this condition would be a disorder of psychosocial aetiology within this framework.
      Grading systems for specific conditions
      Two additional sources in our review described frameworks for specific conditions: benign mid-membranous vocal fold lesions (BVFL)
      • Rosen CA
      • Gartner-Schmidt J
      • Hathaway B
      • et al.
      A nomenclature paradigm for benign midmembranous vocal fold lesions.
      and vocal fold motion impairment.
      • Rosen CA
      • Mau T
      • Hess M
      • et al.
      Nomenclature proposal to describe vocal fold motion impairment.
      These well-structured single-axis frameworks by Rosen and colleagues included detailed nomenclature to define gradings of the respective conditions, together with inclusion and exclusion criteria to help determine classification. The proposed breakdown of terminology and the definitions are good examples of how a framework can facilitate clear communication of the aetiology, assessment findings and treatment planning.42

      Recommended clinical assessments

      We aimed to examine themes in the clinical assessments described by authors for the purposes of classification, as charted in the supplementary file. Most of the authors did not include specific details of the test measures, cut off scores or recommended minimum assessment protocols for classification. Where these were described, the most frequent assessment measures included indirect laryngoscopy (n=13), case history features (n=10), auditory perceptual voice assessment features (n=4), and neck/extrinsic laryngeal palpation (n=3). However, it is difficult to draw comparisons or conclusions for our review based on the available evidence from the included sources.

      Quality assessment

      Study quality indicator ratings of all 20 papers were classified using the Joanna Briggs Institute (JBI) Level of Evidence (LOE) descriptions.
      • Peters MDJ GC
      • McInerney P
      • Baldini Soares C
      • et al.
      Chapter 11: scoping reviews.
      Each paper was critically appraised using the relevant subsection of the JBI critical appraisal tool
      • Peters MDJ GC
      • McInerney P
      • Baldini Soares C
      • et al.
      Chapter 11: scoping reviews.
      and are detailed in Tables 5, 6, 7 and 8. Most of the sources (n=13) were articles of text and opinion. The remaining seven papers included studies using a case series (n=5), case-controlled study (n=1) and analytical cross-sectional study (n=1), indicating the sources of evidence are generally of low quality.
      TABLE 5Risk of Bias Assessment of Included Studies Using the Joanna Briggs Institute (JBI) Appraisal Tool
      Text and OpinionDamste, 1973.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      Hacki et al, 2022.
      • Hacki T
      • Moerman M
      • Rubin JS
      Malregulative’ rather than ‘Functional’ dysphonia: a new etiological terminology framework for phonation disorders—a position paper by the Union of European Phoniatricians (UEP).
      Hillman et al, 2020.
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      Milutinovic, 1996.
      • Milutinovic Z
      Classification of voice pathology.
      Morrison and Rammage, 1993.
      • Morrison MD
      • Rammage LA
      Muscle misuse voice disorders: description and classification.
      Van Houtte et al, 2011.
      • Van Houtte E
      • Van Lierde K
      • Claeys S
      Pathophysiology and treatment of muscle tension dysphonia: a review of the current knowledge.
      Rosen et al, 2016.
      • Rosen CA
      • Mau T
      • Hess M
      • et al.
      Nomenclature proposal to describe vocal fold motion impairment.
      Rosen and Murray, 2000.
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      Arnold and Pinto, 1960.
      • Arnold GE
      • Pinto S
      Ventricular dysphonia: new interpretation of an old observation.
      Bradley, 2010.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      Butcher et al, 2007.
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      Verdolini et al, 2005.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      Spencer, 2015.
      • Spencer ML
      Muscle tension dysphonia: a rationale for symptomatic subtypes, expedited treatment, and increased therapy compliance.
      Is the source of the opinion clearly identified?NYYYYYYYUCYYYY
      Does the source of opinion have standing in the field?UCYYUCYUCYYUCUCYYUC
      Are the interests of the relevant population the central focus of the opinion?UCYYYYYYYUCYYYY
      Is the stated position the result of an analytical process, and is there logic in the opinion expressed?UCYYNYYYNYYYYY
      Is there reference to the extant literature?NUCUCNYYNNNUCYNY
      Is any incongruence with the literature/sources logically defended?NUCUCNANNUCNUCUCYNY
      Abbreviations: N, no; NA, not applicable; UC, unclear; Y, yes. †manuscript in press at the time of review.
      TABLE 6Risk of Bias Assessment of Included Studies Using the Joanna Briggs Institute (JBI) Appraisal Tool
      Analytical Cross-Sectional StudiesFernandez, 2020.
      • Fernández S
      • Garaycochea O
      • Martinez-Arellano A
      • et al.
      Does more compression mean more pressure? A new classification for muscle tension dysphonia.
      Were the criteria for inclusion in the sample clearly defined?Y
      Were the study subjects and the setting described in detail?Y
      Was the exposure measured in a valid and reliable way?UC
      Were objective, standard criteria used for measurement of the condition?Y
      Were confounding factors identified?Y
      Were strategies to deal with confounding factors stated?UC
      Were the outcomes measured in a valid and reliable way?N
      Was appropriate statistical analysis used?N
      Abbreviations: N, no; NA, not applicable; UC, unclear; Y, yes.
      TABLE 7Risk of Bias Assessment of Included Studies Using the Joanna Briggs Institute (JBI) Appraisal Tool
      Case SeriesBaker et al, 2007.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      Aronson et al, 1966.
      • Aronson AE
      • Peterson Jr., HW
      • Litin EM
      Psychiatric symptomatology in functional dysphonia and aphonia.
      Koufman and Blalock, 1982.
      • Koufman JA
      • Blalock PD
      Classification and approach to patients with functional voice disorders.
      Morrison et al, 1986.
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      Rosen et al, 2012.
      • Rosen CA
      • Gartner-Schmidt J
      • Hathaway B
      • et al.
      A nomenclature paradigm for benign midmembranous vocal fold lesions.
      Were there clear criteria for inclusion in the case series?YYYUCY
      Was the condition measured in a standard, reliable way for all participants included in the case series?YNNYY
      Were valid methods used for identification of the condition for all participants included in the case series?YUCNUCY
      Did the case series have consecutive inclusion of participants?YUCUCYUC
      Did the case series have complete inclusion of participants?YUCUCYN
      Was there clear reporting of the demographics of the participants in the study?YNNNN
      Was there clear reporting of clinical information of the participants?NNNNY
      Were the outcomes or follow up results of cases clearly reported?NANANNAY
      Was there clear reporting of the presenting site(s)/clinic(s) demographic information?NANNUCY
      Was statistical analysis appropriate?YNNNY
      Abbreviations: N, no; NA, not applicable; UC, unclear; Y, yes.
      TABLE 8Risk of Bias Assessment of Included Studies Using the Joanna Briggs Institute (JBI) Appraisal Tool
      Case Control StudiesHillman et al, 1989.
      • Hillman RE
      • Holmberg EB
      • Perkell JS
      • et al.
      Objective assessment of vocal hyperfunction: an experimental framework and initial results.
      Were the groups comparable other than the presence of disease in cases or the absence of disease in controls?UC
      Were cases and controls matched appropriately?UC
      Were the same criteria used for identification of cases and controls?UC
      Was exposure measured in a standard, valid and reliable way?No
      Was exposure measured in the same way for cases and controls?UC
      Were confounding factors identified?Y
      Were strategies to deal with confounding factors stated?Y
      Were outcomes assessed in a standard, valid and reliable way for cases and controls?UC
      Was the exposure period of interest long enough to be meaningful?NA
      Was appropriate statistical analysis used?N
      Abbreviations: N, no; NA, not applicable; UC, unclear; Y, yes.
      Quality indicator ratings for the sub-set of multi-axis frameworks using the Buchbinder tool for all parameters, including overall quality rating (total score/24), and overall weighted score (mean score of 1 for each category, total score/7) are detailed in Table 9. Four articles had a mean weighted score of less than 3/7, indicating a low level of quality. The remaining 3 studies demonstrated a moderate quality rating with a mean weighted score of greater than 4, one study scoring 5.93. Most studies were author opinion, only 1 study included inter-rater reliability measures.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      TABLE 9Risk of Bias of Multi-axis Frameworks Using the Buchbinder Risk of Bias Tool
      Damste, 1973.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      Morrison et al, 1986.
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      Milutinovic, 1996.
      • Milutinovic Z
      Classification of voice pathology.
      Rosen and Murray, 2000.
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      Baker et al, 2007.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      Bradley, 2010.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      Verdolini et al, 2005.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      PurposeIIs the purpose, population, and setting clearly specified?PYPYYYY
      IIs the domain and all specific exclusions from the domain clearly specified?PPYNYPY
      Are all relevant categories included?YYYYYYY
      IIIs the breakdown of categories appropriate, considering the purpose?YYNPYYY
      Are the categories mutually exclusive?PYPPYYY
      IIIWas the method of development appropriate?NPNNYNY
      IVIf multiaxial, are criteria of content validity satisfied for each additional axis?PYNNYPY
      Face validityIIs the nomenclature used to label the categorised satisfactory?PYNYYYY
      Are the terms used based upon empirical (ie, directly observable) evidence?DKPNNYDKY
      IIAre the criteria for determining inclusion into each category clearly specified?NPNPYYY
      If yes, do these criteria appear reasonable?NAYNANYYY
      Have the criteria been demonstrated to have validity and/or reliability?DKNNNDKDKDK
      IIIAre the definition of criteria clearly specified?NPNPYNY
      IVIf multiaxial, are criteria of face validity satisfied for each additional axis?NPNNYPY
      FeasibilityIIs the classification simple to understand?YYNNYYY
      IIIs the classification easy to perform?DKYPNYYY
      III
      Clinical examination = case history by ENT/SLP including perceptual judgement by ENT/SLP, visualisation of the larynx (laryngoscopy/mirror examination).
      Does it rely on clinical examination alone?
      DKYDKDKNNN
      IV
      Special skills/tools = video stroboscopy, electromyography (EMG), other.
      Are special skills, tools, and/or training required?
      DKNDKDKYYY
      V
      How long does it take to perform = not judged.
      How long does it take to perform?
      NANANANANANANA
      Construct validityIDoes it discriminate between entities that are thought to be different in a way appropriate for the purpose?PDKPDKYDKY
      IIDoes if perform satisfactorily when compared to other classification systems which classify the same domain?DKDKNDKDKDKDK
      ReliabilityIDoes the classification system provide consistent results when classifying the same conditions (test – retest)?DKDKDKNYDKDK
      IIIs the intraobserver and interobserver reliability satisfactory?DKDKDKNYDKDK
      GeneralisabilityIHas it been used in other studies and/or settings?DKYNDKYDKY
      Overall score4154519.510.517
      Overall weighted score (Potential max = 7, mean score out of 1 for each category)1.654.401.291.625.932.674.86
      Abbreviations: DK, don't know; N, no; NA, not applicable; P, partial; Y, yes.
      Scores calculated by summing number of yes (1 point) and partially (0.5 point) responses, except for the item “are special skills, tools and/or training required?” for which a “no” response = 1 point.
      low asterisk Clinical examination = case history by ENT/SLP including perceptual judgement by ENT/SLP, visualisation of the larynx (laryngoscopy/mirror examination).
      Special skills/tools = video stroboscopy, electromyography (EMG), other.
      How long does it take to perform = not judged.

      DISCUSSION

      This scoping review intended to present an overview of the existing frameworks for the classification of voice disorders, including the terminology, definitions, classification criteria and the conditions or diagnoses grouped within the frameworks. In addition, we evaluated the quality of the evidence with respect to published methodological guidance for development of classification frameworks, to recommend a core set of voice disorder classification groups with corresponding classification criteria based on the available evidence. Evidence for clinical assessments and relevant clinical features used in classification was also extracted during the review process, however there was insufficient information for detailed analysis of this information.

      Frameworks, terminology, and definitions for classification of voice disorders

      A total of 20 sources were included in the review and have been summarised according to provisional analysis group labels of hyperfunction-muscle tension, psychosocial and organic aetiologies to aid synthesis of this data. All but one disorder type was easily attributed to one of these three groups. Several sources were incomplete and didn't encompass conditions across all our chosen domains for analysis; whereas others included single classification group labels suggesting one analysis domain over another, but with a heterogenous list of sub-groups or conditions that spanned multiple domains. Although the classification group and subgroup labels provided in these sources varied in frequency, some terms stood out more often than others. This perhaps suggests these represent more developed concepts and have a wider acceptability than those less frequently used.

      Clinical criteria to guide clinicians in classification

      Less than half of the sources provided well-defined classification criteria. Where definitions were included, they were frequently inconsistent with studies using the same or similar terms. Most of the inconsistencies in the criteria described were those placed in our hyperfunction-muscle tension and psychosocial analysis domains. This is not surprising given these disorders can have a variety of signs or symptoms that are not exclusive to a single underlying condition, and perhaps not easily distinguished through medical examination alone. This may also reflect the lack of agreed terminology and defining characteristics available in the literature to date.
      • Roy N
      • Barkmeier-Kraemer J
      • Eadie T
      • et al.
      Evidence-based clinical voice assessment: a systematic review.
      Given the variety in classification criteria provided in these sources, several common themes have been identified which can be considered important in the differential classification of these voice disorders. This includes the clinical history of the symptom progression,
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      secondary signs and observations of increased intrinsic and extrinsic laryngeal tension,
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      ,
      • Hillman RE
      • Holmberg EB
      • Perkell JS
      • et al.
      Objective assessment of vocal hyperfunction: an experimental framework and initial results.
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      and volitional control of the individual to modify their voice with directed instruction from a voice professional.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      For conditions identified in our organic analysis domain, limited criteria could be extracted from the published frameworks. The most comprehensive frameworks included a wide-ranging list of organic conditions grouped in a similar pattern, according to their underlying aetiology with respect to the location of primary breakdown (eg, neurological, structural, trauma).
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      • Bradley PJ
      • et al.
      Voice disorders: classification.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).

      Do existing frameworks satisfy methodological guidelines for classification system development?

      Overall, most studies identified by this review when rated using the Buchbinder risk of bias assessment tool
      • Buchbinder R
      • Goel V
      • Bombardier C
      • et al.
      Classification systems of soft tissue disorders of the neck and upper limb: do they satisfy methodological guidelines?.
      were considered low quality and the majority represented the opinion of a single author or author group, or they described a single case series with a limited description of how patients could be classified in their framework. Three papers were rated moderate quality using a specific risk-of-bias tool designed to assess the methodology of classification frameworks.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      Two of the sources described the use of consensus methodology in the development of their framework,
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      and one of these studies provided additional inter-rater reliability scores to demonstrate validity of their classification groups.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.

      How conditions are classified

      Different methodology was used by the authors for classifying voice disorders across the sources, as demonstrated in Table 3a, Table 3b, Table 3c, Table 4a and Table 4b. The multi-axis frameworks with fewest classification groups classified conditions according to broad aetiologies and their homogenous clinical features (Table 3a). The sub-categories and conditions included under each classification group appeared mutually exclusive, defined by clinical observations from multidimensional voice assessments.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      This was also a common theme in many of the single-axis frameworks (Table 4a). Frameworks where conditions were grouped by the presence or absence of organic pathology did not appear to include all possible conditions and the categories were not mutually exclusive (Table 3b).
      • Rosen CA
      • Murry T
      Nomenclature of voice disorders and vocal pathology.
      • Damste PH
      Vocal disorders. A guide to their diagnosis.
      • Milutinovic Z
      Classification of voice pathology.
      For example, conditions defined by psychological disturbances or those caused by vocal strain were included in categories labelled Organic and Primary Organic. Two authors chose to classify conditions according to the characteristics of underlying aetiology and disease (Table 3c). These contained the greatest number of classification groups and conditions were placed together in line with the location and characteristics of the organic pathology. This may be useful when identifying and communicating the specific organic cause of a presenting voice disorder, where an organic cause exists. However, in these frameworks the categories for voice disorders with no organic cause were not as clearly defined and the labelling of these categories within these frameworks was not as clear, for example other disorders affecting voice.
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).

      Which conditions are included and what clinical assessments determine classification?

      A wide range of disorders were described under each of the classification groups across the multiple frameworks in our review. The heterogeneity in terminology used for these conditions across the sources made comparison very difficult. We have attempted to identify common themes for how these conditions were grouped. The most common themes included sub-classifying conditions with specific organic aetiologies, and sub-classification of observed vocal fold mucosal changes where muscle tension is considered the primary aetiology.
      Due to a lack of detailed information contained within the sources described in this review, we could not address the sub-question of which clinical assessments are described to guide classification. However, the most frequently described clinical assessments included laryngeal examination through indirect laryngoscopy, auditory perceptual features of the voice and patient reported case history information.

      Purpose of a classification framework for voice disorders

      When defining a classification framework, it is important to consider the differences between classification and diagnosis, as well as their intended purpose. Diagnostic criteria are the set of signs, symptoms and tests, clinicians use to guide the process of diagnosis. These should have high levels of sensitivity to identify the different characteristics of a specific disease, whilst accurately distinguishing these features from other diseases.
      • Aggarwal R
      • Ringold S
      • Khanna D
      • et al.
      Distinctions between diagnostic and classification criteria?.
      ,
      • Hunder GG
      • Arend WP
      • Bloch DA
      • et al.
      The American College of Rheumatology 1990 criteria for the classification of vasculitis: introduction.
      Classification criteria on the other hand, are commonly a set of standardized definitions, including signs symptoms and assessment measures, which describe broader well-defined homogenous cohorts of diseases, whilst identifying shared features of a condition.
      • Hunder GG
      The use and misuse of classification and diagnostic criteria for complex diseases.
      The key difference is classification criteria do not include the full spectrum of indications of a disease, but should still have a set of criteria to identify a high proportion of patients and exclude a high proportion with other diseases.
      • Hunder GG
      • Arend WP
      • Bloch DA
      • et al.
      The American College of Rheumatology 1990 criteria for the classification of vasculitis: introduction.
      An internationally approved classification framework should therefore be well accepted, unambiguous, encompass all domains of voice disorders, and be developed using appropriate research designs including consensus methodology, or inter-rater reliability measures.
      • Buchbinder R
      • Goel V
      • Bombardier C
      • et al.
      Classification systems of soft tissue disorders of the neck and upper limb: do they satisfy methodological guidelines?.

      A suggested classification system

      Having reviewed the sources of evidence selected against the review questions, there is no single classification framework that provides well defined labels and definitions to classify all the domains of voice disorders across the spectrum. We have summarised the evidence and common themes from the literature, and have proposed the following terms and defining criteria taken from a selection of existing frameworks be used for the purposes of voice disorder classification in clinical practice and research (Supplementary Figure, Infographic).
      Muscle tension voice disorder/muscle tension dysphonia
      The current review considers Muscle Tension Dysphonia (MTD) or Muscle tension voice disorder the most frequently used and well-defined term for voice disorders with hyperfunctional-muscle tension aetiologies. Additionally, the term is frequently cited in the current voice disorder literature demonstrating it has widespread acceptability. Furthermore, this review supports including sub classifications of benign pathology of the vocal folds when they are clearly identified as contributory or resulting from vocal hyperfunction.
      • Hillman RE
      • Stepp CE
      • Van Stan JH
      • et al.
      An updated theoretical framework for vocal hyperfunction.
      This includes the prefix primary to denote no observable vocal fold changes, secondary to define a MTD with visible vocal fold trauma, and adaptive to define MTD in compensation to a primary organic aetiology.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      Classification criteria described in the published frameworks exclusive to this group of voice disorders include presenting signs or symptoms consistent with muscle hyperfunction in response to vocal demands of the individual
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Van Houtte E
      • Van Lierde K
      • Claeys S
      Pathophysiology and treatment of muscle tension dysphonia: a review of the current knowledge.
      ; observed persistent laryngeal and/or supraglottic muscle constriction during phonation
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      ; improved voice, laryngeal observations, or perceived effort with specific targeted postures or reflex activities.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      Functional (psychogenic) voice disorder
      The two most frequently used terms for voice disorders of psychosocial aetiology, are psychogenic and functional. Our proposal is to adopt the term functional and the classification criteria as it pertains to voice disorders, as proposed in the most recent body of literature on Functional Neurological Disorders (FND).
      • Baker J
      • Barnett C
      • Cavalli L
      • et al.
      Management of functional communication, swallowing, cough and related disorders: consensus recommendations for speech and language therapy.
      The term functional has wide acceptance by neurologists and psychiatrists to classify disorders with motor and/or sensory signs or symptoms not explained by recognised neurological disorders. Recently an international multidisciplinary group of experts have agreed FND is a widely accepted classification term for a range of functional conditions, including dysphonia.
      • Baker J
      • Barnett C
      • Cavalli L
      • et al.
      Management of functional communication, swallowing, cough and related disorders: consensus recommendations for speech and language therapy.
      In addition, we propose that keeping the term psychogenic may help to avoid confusion, where historically functional has been used by SLPs and ENTs as a classification term encompassing both muscle tension and psychogenic aetiologies.
      This review suggests we should avoid classification of these conditions using a process of diagnostic exclusion, as these voice disorders may not always be defined exclusively through a history of known conflicts or stressors in the presence of specific vocal characteristics and visible laryngeal tension.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      However, several exclusive features defined by Baker, Butcher and Aronson can be used to clearly identify them from other groups, most notably loss of voluntary motor control on the vocal sub-systems or an individual's inability to self-regulate initiation of optimal voice, albeit involuntary normal function may frequently be observed.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Morrison MD
      • Nichol H
      • Rammage LA
      Diagnostic criteria in functional dysphonia.
      ,
      • Butcher P
      • Elias A
      • Cavalli L
      Understanding and Treating Psychogenic Voice Disorder: A CBT Framework. Wiley Series in Human Communication Science.
      In our review, the voice disorder commonly termed puberphonia or adolescent transitional dysphonia was the only condition that could not be placed into our provisional analysis domains. We have grouped this condition within the functional (psychogenic) classification group based on classification criteria provided by Baker and the ASHA SIG-3 group.
      • Baker J
      • Ben-Tovin DI
      • Butcher A
      • et al.
      Development of a modified diagnostic classification system for voice disorders with inter-rater reliability study.
      ,
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      However, we acknowledge the aetiology of this disorder can be multifactorial and may not always meet the criteria of a functional disorder. For the purposes of this review, we have placed it as a sub-group with criteria that identifies this condition by non-organic aetiology, that is, in the presence of normal hormonal development.
      Organic voice disorders defined by etiological group
      Diagnostic criteria for specific voice disorders or diseases of the vocal tract that arise from organic or neurogenic causes are frequently well-defined in the literature. However, there remains a need for commonly understood classification terminology where groups of homogenous disorders with similar defining criteria can be placed. Existing frameworks most frequently group conditions according to broad aetiologies and the area of breakdown within the upper aerodigestive tract. The most comprehensive example is detailed in the classification manual for voice disorders-I (CMVD-I).
      • Verdolini K
      • Rosen C
      • Branski R
      • et al.
      Classification Manual for Voice Disorders-I (1st ed.).
      This model demonstrated a high-quality rating in our assessment, is easy to follow, and the disorders are grouped appropriately to their underlying aetiology where organic conditions are concerned. For each classification group the model provides a comprehensive list of specific conditions with well-defined organic or neurogenic pathophysiology. In addition, the frameworks for BVFL and vocal fold immobility
      • Rosen CA
      • Mau T
      • Hess M
      • et al.
      Nomenclature proposal to describe vocal fold motion impairment.
      ,
      • Rosen CA
      • Gartner-Schmidt J
      • Hathaway B
      • et al.
      A nomenclature paradigm for benign midmembranous vocal fold lesions.
      are examples of classification systems where specific terminology and clearly defined criteria can be used to aid the communication of both diagnosis and treatment planning.

      Pathway to a universal classification system

      Based on this review, more research is needed to establish a universally accepted classification system in voice disorders. The necessary steps to this outcome would include an international multi-disciplinary approach using well established consensus methodology such as a Delphi process. The aim would be to reach agreement on i) the terminology to label common groups of voice disorders for the purpose of classification; ii) nomenclature for specific diagnoses or conditions of voice disorders that are often poorly defined in the literature (eg, FND, Puberphonia); iii) high quality research using standardised assessment approaches to define the common clinical features of all voice disorders, with measures of inter-rater reliability to enable consistent classification under an agreed framework. A framework with international acceptance could promote international collaboration and greatly improve evidence-based clinical research in the field of voice disorder diagnostics, as well as improving communication between professionals when planning treatment for voice disorders.

      Limitations

      To our knowledge, this is the first scoping review to examine the frameworks and terminology used to define voice disorders across the full range of aetiologies within the health sciences literature. Nevertheless, there are some limitations to our review. We only reviewed English language studies, however very few non-English papers were identified in our searches, and thus unlikely to have had a substantial impact on the findings of our review. We incorporated critical appraisal and risk of bias on selected multi-axis frameworks to facilitate a quality assessment, but acknowledge this is not a requirement or in some examples a recommendation of scoping reviews. Unlike systematic reviews that are aimed at a narrow range of evidence and may require quality assurance, scoping reviews are less concerned with a specific question and the sources of evidence are from a much broader search.
      • Arksey H
      • O’Malley L
      Scoping studies: towards a methodological framework.
      The decision to include a quality assessment was considered important to help determine a core set of classification terminology and criteria, which was an objective of our review.

      CONCLUSIONS

      Many classification frameworks have been proposed for use with disorders of voice and have been summarised as part of this scoping review in the endeavour to propose a framework for clinical and research use in the future. Most frameworks are of low-quality evidence with no discussion of the method of how they have been devised. Almost half of the terms presented have poorly defined classification criteria and are not widely used within the current scientific literature. No single classification system provides clearly defined distinctions across the full spectrum of aetiologies. However, several key themes are presented together with a core set of suggested terms and definitions for the broad classification of voice disorders. We propose a classification framework which will require future international and interdisciplinary consultation, and evaluation. Continued high quality research studies using consensus methodology and inter-rater reliability scores is recommended to determine agreement of the labels used to classify homogonous groups of voice disorders and determine inclusion of specific conditions under each of the classification groups.

      Declarations of competing interest

      None

      Acknowledgments

      The authors would like to acknowledge the assistance and expertise of Ms. Elaine Tam, Librarian for the Faculty of Medicine and health, The University of Sydney, and Ms. Sarah Thorning, Librarian at Gold Coast University Hospital.

      Appendix I: Search strategy

      Tabled 1
      SearchQueryRecords retrieved
      #1Voice disorders/OR Voice disorder*.mp OR Laryngeal disorder*.mp OR Vocal disorder*.mp OR Vocal fold*.mp OR Dysphonia.mp OR Organic voice disorder*.mp OR Organic dysphonia*.mp OR laryn* structural.mp OR laryn* inflammation.mp OR laryngeal disease*.mp OR Functional voice disorder*.mp OR Functional dysphonia*.mp OR Functional-muscle tension voice disorder*.mp OR Muscle tension dysphonia*.mp OR Muscle tension voice disorder*.mp OR Muscle misuse dysphonia*.mp OR Muscle misuse voice disorder*.mp OR Ventricular dysphonia*.mp OR Non organic voice disorder*.mp OR Functional-psychogenic voice disorder*.mp OR Psych* voice disorder.mp OR Psych* voice disorders.mp OR Functional neurological voice disorder*.mp OR Neuro* voice disorder.mp OR Neuro* voice disorders.mp OR Neuro* dysphonia.mp or Neuro* dysphonia.mp21235
      #2Description.mp OR Descriptor*.mp OR “international classification of diseases”/OR Classification*.mp OR Classification/OR Classification criteria.mp OR Classification terminology.mp OR Framework*.mp OR Practice guideline/OR Guideline*.mp1684932
      #31 AND 21400
      Limited to (english language and humans and yr = “1900-current”)1041

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