Functional voice disorders (FVDs) stem from unhygienic use of the vocal mechanism, with the absence of anatomical or neurological abnormalities (Naqvi & Gupta, 2021). Voice disorders have a prevalence rate of 7.5% in the United States of America (US) (Cohen et al., 2017); yet specific incidence rates as well as the nature of FVDs have been inadequately reported globally.

Functional voice disorders can include, but are not limited to, vocal fatigue, muscle tension dysphonia (MTD), diplophonia, ventricular phonation and psychogenic voice disorders (Naqvi & Gupta, 2022). Functional voice disorders are known to reduce job performance and, ultimately, quality of life (Behlau et al., 2012). As such, vocal quality, pitch and loudness can be impaired without any contributing anatomical or neurological impairments (Chung et al., 2018). Given the varying nature of FVDs, treatment will differ (Naqvi & Gupta, 2021). Thus, describing the incidence and nature of FVDs will guide professionals to render appropriate services from the onset.

A substantial proportion of the labour force consists of professionals who rely on their voice, also known as occupational voice users (OVUs) (Roy et al., 2016). An OVU is defined as an individual who requires their voice to complete their day-to-day work activities (Phyland & Miles, 2019). This can include, but is not limited to, singers, stage performers, sports coaches, sales assistants, teachers, lecturers, lawyers, telephone operators, call centre workers, receptionists, priests and health professionals (Phyland & Miles, 2019). More longitudinal studies are needed to follow the development and treatment of FVDs (Cantor Cutiva et al., 2013). Most OVUs are at an increased risk of developing an FVD (Phyland & Miles, 2019). This has been illustrated in the literature among the teaching (Cantor Cutiva et al., 2013), singing (Ravall & Simberg, 2020) and physician populations (El Tayeb & Abdo, 2012).

Functional voice disorders among the OVU population limit a professional’s working capacity and have health implications that require medical, speech and psychological intervention (Al-Saleem & Alsaleem, 2013). Management of voice disorders is a costly public health challenge, because of medical treatment and its impact on the workforce and employment (Cohen et al., 2017). In the US, voice disorders are estimated to cost $5 billion annually, combining direct healthcare costs and indirect costs related to work absenteeism and presenteeism (Cohen et al., 2017). Consultations with general medical practitioners (GMPs) appear to be counterproductive for voice problems as they do not have sufficient knowledge of voice disorders to ensure adequate intervention (Cohen et al., 2017). Therefore, patients with FVDs do not receive an otorhinolaryngology evaluation upon entry, and this often results in inaccurate diagnoses and inappropriate treatment, which adds to treatment costs. Epidemiological data have a direct effect on service delivery as they enable an earlier and correct diagnosis (Cohen et al., 2017). This also enables rapid and appropriate service provision while decreasing costs (Cohen et al., 2017).

Research carried out in Saudi Arabia found that 80.9% of male teachers from a sample size of 340 teachers had experienced voice-related problems in the previous year (Al-Saleem & Alsaleem, 2013). A systematic review conducted in the Netherlands reported a point prevalence of 9% – 37% and a 12-month prevalence of 15% – 80% of voice disorders among teachers in both low- and middle-income countries (LMICs) and high-income countries (HICs); of which three publications included a clinically verified prevalence of 17% – 57% and seven studies reported a lifetime prevalence of 51% – 69% (Cantor Cutiva et al., 2013). Within the teaching population, both HICs (including Saudi Arabia, the Netherlands, the United States, Finland and Latvia) and LMICs (such as Iran) produced similar results regarding prevalence. Thus, the incidence of FVDs has been inadequately recorded globally.

Epidemiological studies aimed at determining the frequency of voice disorders in several populations in Brazil, Iran, Latvia, Finland and Egypt. Teachers in Brazil (Behlau et al., 2012), Iran (Seifpanahi et al., 2016) and Latvia experienced a voice disorder in their lifetime (Trinite, 2017). A study conducted in Finland investigated the association between choir singing and voice disorders, and 21% presented with an FVD because of their vocally harmful behaviour (Ravall & Simberg, 2020). Similarly, the prevalence of FVDs in Egypt was significantly higher among private physicians when compared to lab physicians (El Tayeb & Abdo, 2012). It should be observed that despite the geographical differences and the variant sample sizes, the research findings were similar among the different populations.

Most studies, which investigated the incidence and/or prevalence of FVDs, were conducted and published in HICs, particularly in North America and Europe. Studies carried out in Asia were conducted in Saudi Arabia and Iran, while one study in Africa was carried out in Egypt. It is important to observe that other continents, including South America and Australia, did not yield any literature pertaining to the incidence of FVDs. Studies exploring the incidence and prevalence of FVDs are evidently needed in LMICs because of the limited published research available.

To date, there is no research available on FVDs in South Africa (SA). Therefore, there is a need to pursue research in this area as it is a global health challenge. Information on the nature of FVDs that are diagnosed and managed within the South African population will advocate for optimum management including prevention and rehabilitation services (Tenny & Boktor, 2022). The high incidence and prevalence of FVDs, especially in OVUs, substantiate the need for prevention strategies, early identification and treatment of FVDs (Fourie et al., 2017). In addition, data on the incidence of FVDs may inform the aetiology of the condition, its associated risk factors and its potential outcomes. In turn, these statistics advocate for the allocation of medical resources through efficient planning of service delivery within the interdisciplinary teams consisting of ear, nose and throat (ENT) specialists and speech-language pathologists (SLPs), specifically in LMICs (Cohen et al., 2014).

There is a pressing need for data on FVDs both within the South African context and internationally, owing to limited published research from LMICs. Identifying the incidence of FVDs will provide a better understanding of the nature of the disorder and may inform and improve prevention strategies, address risk factors and improve clinical outcomes. Based on the aforementioned, the following research question is posed: What is the incidence and nature of FVDs in adults at a South African interdisciplinary voice clinic?

The study aimed to describe the incidence and nature of FVDs in adults at an interdisciplinary voice clinic in SA. A retrospective quantitative research design was utilised. Institutional Review Board (IRB) clearance was obtained from the Faculty of Humanities and the Faculty of Health Sciences (Reference number: HUM003/0822) prior to data extraction and data analysis.

Data were extracted from an interdisciplinary Voice Clinic’s secure medical database, where patient-related healthcare information is stored as part of standard patient healthcare records. The data were captured and anonymised during data extraction to ensure confidentiality of personal information was upheld. Male and female participants, over the age of 18 years with a confirmed diagnosis of an FVD, who attended the Voice Clinic between January 2017 and July 2022 were included in the dataset (refer to Table 1).

The data were analysed using the Statistic Package of Social Sciences (SPSS) for Windows, Version 28.0 (IBM Corp., Armonk, NY, United States), which analysed the data by generating descriptive statistics (frequencies and percentages) to summarise the variables and applying inferential tests to examine differences between groups. The extracted data were used to determine the incidence of FVDs among the treatment-seeking population and the nature of the FVD.

Lifestyle and health factors were also explored, and this included hydration, smoking, alcohol consumption, allergies and exercise. The voice handicap index (VHI) was chosen as it is a validated and widely used tool that allows reliable comparison across groups (Caffier et al., 2021).

Descriptive and inferential statistics were used. In the analysis, the Mann–Whitney test was employed to assess potential differences between non-occupational and OVUs. The statistic was utilised for comparisons and for interpretation to understand potential significant differences between OVUs and non-OVUs in relation to p-values.

Out of the total number of patients who attended the voice clinic (n = 516) between January 2017 and July 2022, 86 (16.67%) patients were diagnosed with an FVD. The data from the 86 patients with FVDs were analysed for this study. From the sample, 24.4% (n = 21) were male patients and 75.6% (n = 65) were female patients. Their ages ranged from 18 years to 77 years old (mean = 47.26; standard deviation [s.d.] = 13.643). Many patients who presented with a primary diagnosis of an FVD (100%) presented with a secondary ENT-related diagnosis (58.1%; n = 50). The most prevalent primary diagnoses of FVDs were MTD (80.2%; n = 69) followed by functional dysphonia (12.8%; n =11).

Naqvi and Gupta (2022) describe MTD as one of the most common types of FVDs, although the terms MTD, functional dysphonia and hyper-functional dysphonia are also used interchangeably. Muscle tension dysphonia causes hypertonicity of the laryngeal musculature, which restricts the vocal folds’ capacity to abduct and adduct with co-ordination and the required speed (Naqvi & Gupta, 2022). Functional dysphonia occurs when the extrinsic and intrinsic laryngeal muscles are dysregulated (Roy, 2003).

Furthermore, 39.5% (n = 34) of patients presented with laryngeal pharyngeal reflux (LPR) as a secondary diagnosis; while 26.41% (n = 23) had abnormal RSI scores (mean = 23.01; s.d. = 14.365). Most of the patients (n = 65; 75.6%) scored high on the VHI (mean = 67.00; s.d. = 34.710). Muscle tension dysphonia may appear as both a primary and secondary diagnosis, as recorded by the ENT in the dataset. Table 2 summarises the diagnoses.

Lifestyle and health factors that were explored included hydration, smoking, alcohol consumption, allergies and exercise. The results are reflected in Table 3. While 18.6% (n = 16) of the participants had inadequate hydration (i.e. consumed less than two litres of water a day), 3.5% (n = 3) exercised moderately. Most of the participants (73.3%, n = 63) were non-smokers and 8.2% (n = 7) were smokers, while 41.9% (n = 36) did not consume alcohol. The majority of the participants (75.6%; n = 65) did not have any allergies.

The perceptual assessment of voice quality of 65 participants (75.58%) was analysed using the Grade, Roughness, Breathiness, Asthenia, Strain (GRBASI) scale.

The mean for each of the GRBASI scores ranged between 0 and 3 for each component, namely grade; roughness; breathiness; asthenia; strain; instability; where 0 = normal; 1 = slight, 2 = moderate, 3 = severe. Among the participants, 26 (30.2%) had a severe grade score, 26 (30.2%) had a slight roughness score, 24 (27.9%) had a normal breathiness score, 24 (27.9%) had a normal asthenia score, 19 (22.1%) had a normal strain score and 25 (29.1%) had a normal instability score. The results can be viewed in Table 4.

Most participants reported multiple signs and symptoms relating to the function of their voice. The most common symptoms reported were hoarseness (n = 58; 67.4%), throat irritation (n = 23; 26.7%), aphonia (n = 17; 19.8%), globus (n = 19; 22.1%), vocal fatigue (n = 18; 20.9%), difficulty with projection (n = 17; 19.8%) and increased throat clearing (n = 19; 22.1%). Other symptoms included: high-pitched voice (n = 6; 7.0%), low pitched voice (n = 3; 3.5%), strained voice (n = 13; 15.1%), loss of breath support (n = 9; 10.5%), chronic cough (n = 4; 4.7%), poor intelligibility (n = 1; 1.2%), painful voice (n = 5; 5.8%) and weak voice (n = 11; 12.8%). Psychological symptoms relating to depression and anxiety were also reported (n = 5; 5.8%).

The reported symptoms were analysed according to the number of patients from the sample who experienced one, two or more symptoms. The distribution of reported symptoms among the participants showed that for two patients (2.3%), no symptoms were reported, while 26 (30.2%) reported one symptom and 15 (17.4%) reported two or three symptoms. In addition, 12 patients (14.0%) reported four symptoms, and 9 individuals (10.5%) reported five symptoms. Only 3 individuals reported six or seven symptoms (3.5%) in each category, and 1 individual (1.2%) reported experiencing eight symptoms.

The two groups namely, OVUs versus non-OVUs, categorised according to the use of their voice as indispensable for their work or not, were compared (Phyland & Miles, 2019). There were 31 patients out of the sample population who were OVUs (43.66%; mean = 3.32) and 40 non-OVUs (56.35%; mean = 2.73). According to the results of the Mann–Whitney test, no significant difference between the two groups was observed (p-value = 0.247, z score = 1.156, MW score = 522.000).

Acoustic measures were also analysed. All the correlations between the age of patient, reflux symptom index (RSI), VHI, jitter, shimmer, fundamental frequency, noise-to-harmonic ratio and maximum phonation time were not significantly different as all p-values were > 0.05. The results can be viewed in Table 5.

Patients were frequently referred to the ENT from other specialist medical practitioners (n = 36; 41.9%) and from GMPs (n = 23; 26.7%). Small percentage of patients were self-referred (n = 8; 9.3%) and (n = 2) 2.3% were referred by an SLP. All patients (N = 86; 100%) were referred from the ENT specialist to the SLP for voice therapy.

The incidence rate of 16.67% from a population of patients who attended a voice clinic emphasises the importance of recognising and acknowledging FVDs as a notable health consideration within this population. Although not statistically significant, the gender distribution within the sample, with a majority of females, emphasises the importance of recognising and addressing gender-specific differences in the assessment and management of FVDs. Thus, the research findings align with existing literature, reporting a higher prevalence of voice disorders among women (Bainbridge et al., 2017). This was highlighted by a previous study, which found that females were 56.0% more likely to experience a voice disorder than males (Bainbridge et al., 2017). In another study exploring prevalence of voice disorders, gender was identified as a risk factor contributing to ever-present voice disorders, and women were reported to experience voice disorders more often than men (Lyberg-Åhlander et al., 2019).

In this study, the average age of patients experiencing an FVD was 47.26 years, with a lower prevalence among young and middle-aged adults. In contrast, a higher prevalence of voice disorders was found in women and men older than the age of 85 years in a previous study (Lyberg-Åhlander et al., 2019).

The prevalence of LPR as a secondary diagnosis highlights the significance of considering comorbid conditions in the assessment and management of FVDs. Lechien et al. (2017) found that LPR leads to histopathologic changes in the vibratory margin of the vocal folds, leading to changes in the mucosa and thus, a voice disorder. Furthermore, hoarseness was reported as the most common symptom of FVD in this patient population, which could potentially be related to the presence of LPR (Lechien et al., 2017). There is a need for future research to investigate the pathophysiology of hoarseness relating to and the association and potential causality between LPR and voice disorders, as many participants were diagnosed with LPR (39.5%) in this study. Ear, nose, and throat specialists along with SLPs should ensure a comprehensive package of care, which would address both the primary voice disorder and related health issues to provide holistic care.

The wide array of voice-related signs and symptoms reported by patients describe the multifaceted nature of FVDs. The complexity necessitates a comprehensive assessment that accounts for the diverse complaints of affected individuals, ensuring that underlying causes are thoroughly addressed. The signs and symptoms should be explored in future studies to further describe the nature of FVDs and to explore potential confounding factors as various multiple were explored in the study.

The comparison between OVUs and non-OVUs, while not revealing significant differences, highlights the need to reconsider the factors influencing voice-related issues among this population. Although the VHI may not fully capture the occupational demands of professional voice users, it provided a standardised measure across both groups. Future studies could incorporate occupation-specific instruments to capture these nuances.

Furthermore, the highest prevalence of FVDs was found to be in the teaching and singing occupations. This encourages a broader perspective when considering the risk factors associated with FVDs. This study points to a possible gap regarding the relationship between laryngopharyngeal reflux and FVDs; however, further review of existing literature is needed to confirm whether this gap has already been addressed.

This study contributes to the current body of knowledge surrounding voice disorders in the South African context. It highlighted the need for continued research to explore the risk factors within the population, such as occupation and comorbid conditions. More studies exploring the incidence of FVDs are needed among different populations and healthcare settings (i.e., both private and public) to better understand the incidence of FVDs with a larger sample size. Moreover, the therapeutic outcomes must be explored from an SLP and ENT perspective, along with adherence to therapy.

This study is particularly significant as it provides the first comprehensive insight into the incidence and nature of FVDs in a voice clinic in SA. It outlines the need for further research and the development of strategies for prevention, early identification, and treatment. Given the high incidence and prevalence of FVDs, particularly among OVUs, these data support the need for further research in LMICs, where such disorders may be underreported or underdiagnosed. This study lays the foundation for research on the psychological and emotional impact of FVDs, which could contribute to further unpacking the nature of FVDs. Lastly, more research is needed to better understand the course of FVDs, how they develop, how they change over time, and what therapy outcomes are.

This study was the first of its kind in this context, thus filling a critical gap in the available literature on the incidence and nature of FVDs. The use of interdisciplinary data allowed for a comprehensive analysis and provided a perspective on medical and SLP perspectives. Furthermore, the use of both descriptive and inferential statistics provided a detailed and thorough analysis of the available data.

This study provides significant insights into the landscape of FVDs at a private healthcare clinic in SA, highlighting their noteworthy incidence, gender-specific prevalence, and clinical characteristics. The prevalence of MTD and LPR as primary and secondary diagnoses emphasises the clinical complexity of FVDs. The diversity of reported voice-related symptoms and the comparison of OVUs and non-OVUs emphasise the importance of an interdisciplinary approach. These findings lay the foundation for improved prevention and treatment strategies, ultimately enhancing the quality of life for individuals with FVDs in SA and beyond.