Abstract
Primary Muscle Tension Dysphonia (MTD) occurs in the absence of structural or neurologic etiologies. Patients with MTD are frequently encountered in clinics and are evaluated using multiple measures of voice evaluation. Studies reporting on the correlation of multiple measures of voice evaluation among individuals with MTD are minimal, which led to this study. This single-group correlational study involved 48 participants diagnosed with primary MTD at a tertiary care institute. Multidimensional measures of voice (acoustic, aerodynamic, auditory-perceptual, and self-rating) were obtained from the participants. GRBAS scale, Acoustic Voice Quality Index, Acoustic Breathiness Index, Maximum Phonation Duration, S/Z ratio, Voice Handicap Index, and Vocal Fatigue Index were the variables considered. These measures were correlated using Spearman’s correlation (ρ) within and between different measures of voice evaluation. Several statistically significant (P < 0.05) correlations were found within and across different measures of voice evaluation. Moderate to very high correlations (ρ between 0.48 and 0.87) were found between auditory-perceptual measures and multiparametric acoustic measures. Weak to moderate correlations (ρ between 0.31 and 0.62) were observed between the VHI and its subsections, with GRBAS, AVQI, and ABI. No statistically significant correlations were observed between aerodynamic measures and other measures of voice evaluation. Results from this study suggest that compared to across measures, the correlation between different variables was stronger within each measure of voice evaluation. These findings highlight the need for a multidimensional voice evaluation in patients with MTD.
Keywords: GRBAS, ABI, AVQI, MPD, VHI-10, VFI
Introduction
Primary Muscle Tension Dysphonia (MTD) is defined as “a change in voice quality and flexibility, in the absence of any structural, systemic, or neurological changes to the subsystems of voice” [1]. Individuals with MTD are frequently encountered in clinics, contributing 8 to 45% of treatment-seeking populations [2, 3]. MTD can arise from misuse of the vocal system, owing to high vocal demands, or can be a learned adaptation from an acute/transient organic condition. MTD can also result from the psychological traits of an individual [1, 4].
MTD is not a unitary disorder. The varied involvement of muscle groups and other laryngeal structures leads to different subtypes of MTD. To date, there is no universally accepted categorization system for the subtypes of MTD [5]. Depending on the laryngeal structures and the muscle groups involved, the following four subtypes of MTD have often been recommended [4, 6]. MTD type I (MTD I) is often manifested as a laryngeal isometric contraction with posterior glottic chink. MTD type II (MTD II) corresponds to the lateral-medial (L-M) compression of the ventricular folds. MTD type III (MTD III) is visualized as an anteroposterior contraction, with the epiglottis falling posteriorly. MTD type IV (MTD IV) is a combination of MTD II and III and is often seen as an absolute supraglottic closure.
In the literature, MTD has been described as a range of disturbed vocal fold behaviors arising from intensified tension in the laryngeal muscles [4]. Although dysphonia due to MTD manifests as variations in quality, pitch, or loudness, the clinical presentation of MTD is varied [1]. Available literature [7, 8] evidences the use of varied methods such as visual examination of the larynx, laryngeal palpation, auditory-perceptual evaluation of voice, acoustic evaluation of voice, measurement of aerodynamic measures of voice for the clinical diagnosis of MTD. Thus, the use of varied methods for the clinical evaluation of MTD accentuates the need to utilize a multidimensional approach, similar to other types of dysphonia [9, 10].
Although MTD presents as a hyperfunction of the muscular structures of the larynx on laryngeal visualization, the continuum of perceived severity of MTD can vary from the perspective of individuals with MTD and the clinician [1]. Furthermore, considering the International Classification of Functioning, Disability and Health (ICF) framework put forth by the World Health Organization [11] for health-related conditions, it is necessary to gather information about different domains of body structures, function, activity participation and the contextual factors (personal and environmental) [11]. Thus, there is a need to evaluate the multidimensional aspects of the disorder in individuals with dysphonia. A multidimensional approach to voice evaluation in individuals with MTD can include laryngeal visualization, auditory-perceptual measures, acoustic measures of voice, aerodynamic measures of voice, and patient-reported measures of quality of life [9, 10].
Based on the current clinical scenario in India, the evaluation of individuals with dysphonia involves a team approach comprising of an otolaryngologist and a speech-language pathologist. Case history forms the base of evaluations. Clinical examination of any patient with voice-related complaints is followed by a laryngeal visualization procedure by the otolaryngologist (such as indirect laryngoscopy, endoscopy, or stroboscopy). Further, the speech-language pathologist evaluates the quality of voice subjectively through auditory-perceptual measures. For this purpose, either the GRBAS scale [12] or the Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V) [13] is utilized. Then, voice samples are recorded for objective evaluations. This involves deriving various acoustic measures from the recorded voice samples. Traditionally, information on pitch, intensity, perturbation, and signal-to-noise ratios were derived as acoustic measures from sustained vowel phonation [14]. More recently, multiparametric acoustic measures of voice evaluation, such as the Acoustic Voice Quality Index (AVQI) and Acoustic Breathiness Index (ABI), are being frequently utilized as clinical acoustic measures of voice quality [15]. These multiparametric measures combine spectral and cepstral measures and are derived from a concatenated signal of continuous speech and sustained vowel phonation samples, thereby increasing their ecological validity [16]. Clinicians often evaluate for different aerodynamic parameters as well. These aerodynamic parameters could merely be Maximum Phonation Duration (MPD) and S/Z ratio or determine complex objective aerodynamic parameters such as phonation threshold pressure, laryngeal airway resistance, or estimated subglottic pressure. Clinicians also probe into several patient-reported outcome measures or self-rating measures to report on the impact of dysphonia on the quality of life of patients. The Voice Handicap Index [17] and the Vocal Fatigue Index [18] are two fundamental self-rating measures widely applied in voice clinics nationwide.
Need of the Study
To date, individual measures of voice evaluation have been reported and correlated among individuals with MTD [5, 19, 20]. Studies reporting correlations across multiple measures of voice evaluation are minimal. The findings from these studies [5, 19, 20] have been diverse, with results suggesting no correlation to strong correlation among multiple measures of voice evaluation. Although some studies in the past have examined the correlation of different measures of voice evaluation in the Indian dysphonic population [21], the correlation of multiple measures of voice evaluation among individuals with MTD is unknown, which led to this study. The use of multidimensional voice analysis involving different measures of voice evaluation can yield comprehensive information about the patient’s condition. Evaluating the correlation of multiple measures of voice evaluation from the same group of patients will provide more meaningful insights into the clinical characteristics of Muscle Tension Dysphonia.
Aim and Objectives
This study aimed to explore the correlation between various measures of voice evaluation (auditory-perceptual, acoustic, aerodynamic, and self-rating) among individuals with MTD. Specifically, parameters within each measure of voice evaluation were correlated to one another (within measure). In addition, parameters were also correlated across each measure of voice evaluation (across measures).
Method
Study Design and Sampling
This study followed a single-group correlational design. We employed consecutive sampling to recruit participants. From consecutive patients who visited a tertiary care training institute from June 2022 to June 2023, those diagnosed with primary MTD and who consented to participate were considered. This study also received clearance from the ethical committee of the institute wherein this study was carried out.
Participants
A total of 48 participants were involved in this study. Table 1 represents the demographic details of the participants. All the participants of the present study were diagnosed as having MTD by experienced otolaryngologists through endoscopy or stroboscopy as deemed necessary. The participants were free of other organic conditions affecting the larynx. Table 2 represents the distribution of participants’ sex across each subtype of MTD. The participants were distributed across different professions with varied vocal demands. All participants had a minimum of preliminary education to read the text in the Kannada language. They were also free of hearing disorders based on self-reports.
Table 1.
Demographic details of the participants
| Participants | |||
|---|---|---|---|
| Male | Female | Total | |
| N | 28 | 20 | 48 |
| Mean Age (in years) | 45.25 ± 13.28 | 39.60 ± 10.96 | 42.60 ± 12.56 |
| Age Range (in years) | 19–71 | 26–59 | 19–71 |
Table 2.
Distribution of participants across subtypes of muscle tension dysphonia
| Number of participants | ||
|---|---|---|
| Male | Female | |
| MTD I | 03 | 03 |
| MTD II | 11 | 04 |
| MTD III | 07 | 13 |
| MTD II & III (MTD IV) | 07 | 00 |
| Total | 28 | 20 |
Data Collection
Data was collected in a soundproof room with appropriate SNR levels [22]. Voice recordings were obtained using an AKG C417PP microphone mounted on a RØDE lav-headset head mount. Thus, a constant mouth-to-microphone distance of approximately 5–6 cm with a 45º to 90º angle was maintained throughout the recording [23]. The microphone was connected to a laptop computer through an audio interface (Focusrite Scarlett 2i2). Recordings were obtained in the program Praat (v.6.2.10) at 44.1 kHz, 16-bit resolution. We obtained two recordings of the participants reading the standardized Kannada reading passage and three trials of maximum phonation duration (MPD) of vowel /a:/ and fricatives /s/ and /z/. Along with these voice recordings, participants completed two self-rating measures: Voice Handicap Index-30 (VHI-30) in Kannada [24] and Vocal Fatigue Index- Kannada (VFI-K) (Rajasudhakar, unpublished data).
Analysis
Acoustically, two multiparametric measures of voice (Acoustic Voice Quality Index (AVQI) [25] and Acoustic Breathiness Index (ABI) [26]) were derived using excerpts from the reading passage (standardized syllable number - “SSN”) [27] and sustained vowel phonation (stable middle three-second portion obtained from MPD task - “SV” [27]). Perceptually, the GRBAS rating was carried out for the concatenated samples of SSN and SV. Three raters with a minimum experience of 5 years after obtaining a postgraduate degree in Speech-Language Pathology carried out the GRBAS rating. The voice samples were presented to the raters in a random order through a customized script in Praat [27]. Anchor voice samples were used to familiarize the raters with the GRBAS rating procedure [28]. Mean ratings for each parameter of the GRBAS scale were considered for further analysis.
Regarding aerodynamic measures, the MPD of the vowel /a:/ was considered for further analysis. In addition, the MPD of the fricatives /s/ and /z/ were used to obtain the S/Z ratio and considered for further analysis. Concerning self-rating measures, the scores of each domain of VHI-30, along with the total score of VHI-30 [24] and VHI-10 [29], were derived. From VFI-K, scores of the three domains were considered for statistical analysis.
Statistical Analysis
All statistical procedures were performed using R Studio (v.2023.09.1 + 494) [30] and IBM SPSS® software version 26. Inter-rater reliability of the auditory-perceptual measurements was examined using Fleiss’ Kappa (Fκ). Before examining the correlations, differences between the subtypes of MTD were checked using the Independent Samples Kruskal Wallis test. Descriptive statistics of each variable under study were derived. Further, the correlation coefficient considered for this study was Spearman’s rho (ρ) with an α level of 0.05. Package “corrplot v.0.92” [31] was employed in R Studio to determine the correlation coefficients between the variables involved in this study and the statistical significance.
Results
Inter-Rater Reliability
While examining the inter-rater reliability, we found the Fκ value to be 0.529 (95% confidence interval of 0.422 to 0.635). This corresponded to a moderate to substantial agreement [32] between the raters on the auditory-perceptual evaluation of the voice samples.
Differences Between Sub-Groups of Muscle Tension Dysphonia
Results of Independent Samples Kruskal Wallis test revealed a lack of statistically significant differences (P > 0.05) between the four subtypes of MTD for most variables considered in this study. Only one exception was the roughness of the GRBAS scale (χ2(3) = 9.270, P = 0.026). Further pairwise comparisons adjusted by Bonferroni corrections for multiple tests revealed that the subtype MTD IV had a higher mean roughness rating than the MTD III subtype (P = 0.030). Despite this isolated finding, participants in all subtypes of MTD were considered as a single group for the correlational analysis. The descriptive data of the participants for all the 17 variables considered in this study are tabulated in Table 3.
Table 3.
Descriptive data of the participants for the variables considered in this study
| Measure | Variable | Mean (SD) | Median (IQR) | 95% Confidence Interval | ||
|---|---|---|---|---|---|---|
| Lower limit | Upper limit | |||||
| Auditory-Perceptual | Grade of GRBAS (G) | 01.29 (00.76) | 01.00 (01.33) | 01.07 | 01.51 | |
| Roughness of GRBAS (R)* | MTD I & MTD II | 01.25 (00.73) | 01.00 (01.33) | 00.92 | 01.59 | |
| MTD III | 00.80 (00.73) | 00.67 (01.42) | 00.46 | 01.14 | ||
| MTD IV | 01.81 (00.79) | 02.00 (01.33) | 01.07 | 02.54 | ||
| Breathiness of GRBAS (B) | 01.10 (00.81) | 01.17 (01.33) | 00.87 | 01.34 | ||
| Asthenia of GRBAS (A) | 00.86 (00.80) | 00.67 (01.25) | 00.63 | 01.09 | ||
| Strain of GRBAS (S) | 00.91 (00.81) | 00.67 (01.33) | 00.67 | 01.15 | ||
| Acoustic | Acoustic Voice Quality Index v.03.01 (AVQI) | 02.83 (01.57) | 02.72 (02.15) | 02.37 | 03.29 | |
| Acoustic Breathiness Index (ABI) | 03.82 (01.48) | 03.77 (02.03) | 03.39 | 04.25 | ||
| Aerodynamic | Maximum Phonation Duration (MPD) | 10.81 (04.41) | 09.81 (06.20) | 09.53 | 12.09 | |
| S/Z Duration (S/Z) | 01.23 (00.42) | 01.11 (00.43) | 01.11 | 01.35 | ||
| Self-Rating | VHI-Functional (VHI-F) | 17.77 (10.25) | 20.50 (17.75) | 14.79 | 20.75 | |
| VHI-Physical (VHI-P) | 20.40 (10.00) | 21.00 (18.75) | 17.49 | 23.30 | ||
| VHI-Emotional (VHI-E) | 12.98 (10.55) | 11.00 (19.25) | 09.92 | 16.04 | ||
| Total score of VHI-30 (VHI-30) | 51.15 (27.34) | 61.00 (47.75) | 43.21 | 59.08 | ||
| Total score of VHI-10 (VHI-10) | 19.10 (10.21) | 22.00 (18.00) | 16.14 | 22.07 | ||
| Vocal Fatigue Index- Part 1 (Tiredness) (VFI-i) | 24.65 (12.16) | 28.00 (19.00) | 21.11 | 28.18 | ||
| Vocal Fatigue Index- Part 2 (Physical) (VFI-ii) | 09.00 (06.53) | 09.00 (12.75) | 07.10 | 10.90 | ||
| Vocal Fatigue Index- Part 3 (Changes with rest) (VFI-iii) | 05.94 (03.66) | 06.00 (05.75) | 04.88 | 07.00 | ||
*Values are separated due to statistically significant differences in some subtypes of MTD.
Correlation Within the Measures of Voice Evaluation
The results of the correlation analysis are depicted in Fig. 1. The correlation coefficients were interpreted based on the recommendations of Hinkle et al. (2003). Within the different measures, we observed statistically significant high to very-high correlations (ρ ranging from 0.77 to 0.91) between the mean ratings of the subscales of the GRBAS scale. There was a statistically significant weak negative correlation (ρ = -0.39) between aerodynamic measures of MPD and S/Z ratio. Similarly, within the scores of VHI, moderate to very high correlations (ρ ranging from 0.59 to 0.91) were observed. Scores of subsections of VFI were found to have weak to moderate correlations (ρ ranging from 0.31 to 0.69) with each other. Altogether, correlations between VHI and VFI scores were weak to high. There was a high correlation (ρ = 0.88) between the acoustic measures of AVQI and ABI.
Fig. 1.
Results of correlation analysis
Correlation Between Different Measures of Voice Evaluation
The correlation between different measures of voice evaluation has also been depicted in Fig. 1. Across the measures, correlations were observed to be moderate to very high between acoustic measures and subscales of the GRBAS scale (ρ ranging from 0.48 to 0.87). Acoustic measures were not found to have a statistically significant correlation with aerodynamic measures or the self-rating measure of VFI. Aerodynamic measures were found not to have statistically significant correlations with auditory-perceptual measures and self-rating measures, except for VFI-i (tiredness), wherein a weak correlation (ρ = 0.36) for the S/Z ratio was observed. VHI scores were found to have weak to moderate correlations (ρ ranging from 0.31 to 0.62) with the auditory-perceptual measure of GRBAS and acoustic measures of AVQI and ABI.
Discussion
This study primarily attempted to determine the correlations between different measures of voice evaluation in Kannada-speaking adults with primary Muscle Tension Dysphonia (MTD). Additionally, we also profiled the multidimensional voice characteristics of individuals with primary MTD. To date, as per the author’s knowledge, studies have not attempted to report multiple measures of voice evaluation from individuals with MTD. Although studies in the past have examined individual measures of voice evaluation among individuals with MTD [33–36], this is one of the first studies to report on multiple measures of voice evaluation from the same group of patients.
As tabulated in Table 3, most subscales of the GRBAS scale were found to have mild to moderate impairment in individuals with MTD. Current findings revealed that the perceived severity of dysphonia was higher in MTD IV than in MTD III. Literature evidence that individuals with MTD could present with varied degrees of dysphonia [34]. In the present study, only seven individuals with MTD IV were considered compared to 20 individuals with MTD III. Hence, additional studies are needed to establish and generalize this finding to the population of individuals with MTD.
Among individuals with MTD considered in the present study, the mean scores on the acoustic measures of AVQI and ABI were above the specified cut-off scores for dysphonia in the Kannada-speaking population [27, 35]. Regarding the aerodynamic measures, MPD was lower in individuals with MTD considered in this study compared to the normative for the South Indian population [36]. Similarly, the S/Z ratio was also found to be higher than 1.2 in the voice samples examined in the current study, which is suggestive of laryngeal pathology [37].
Further, individuals with MTD considered in the present study reported that dysphonia resulted in a significant impact on their quality of life. This was evidenced by the mean scores of VHI-30 (51.15) and VHI-10 (19.50) among the individuals with MTD, which were higher than the cut-offs recommended for VHI-30 (≥ 21.5) and VHI-10 (≥ 6.5) [29]. Findings of the current study also identified individuals with MTD as experiencing vocal fatigue, which is reflected in the higher scores in all the domains of the Vocal Fatigue Index. Altogether, the descriptive data suggests that multiple measures of voice evaluation are impaired in individuals with MTD.
Some earlier studies among individuals with MTD have reported that the auditory-perceptual measures of MTD can overlap with those perceived in neurological or structural lesions [34, 38]. Hence, the use of multidimensional assessment can give valuable insights into the multifaceted nature of MTD and help differentiate it from other conditions. Further, MTD is a condition that has diverse etiological factors [1, 4]. The presence of diverse etiology also necessitates the implementation of multidimensional assessment techniques. However, while implementing a multidimensional assessment, it is necessary to examine whether there is a correlation within and across the different measures, which formed the crux of this study.
The findings of the current study indicate some correlations between multiple measures of voice evaluation, although they examine independent constructs. We found that compared to across measures, the correlation between different variables was stronger within each measure of voice evaluation. Across the different measures of voice evaluation, strong correlations observed between auditory-perceptual measures and acoustic measures uphold the high concurrent validity of these measures [27]. Similar to existing literature [5, 29] weak to moderate correlations were found between the subscales of the GRBAS scale and the total scores and scores on the sub-domains of the VHI. On auditory-perceptual evaluation of voice quality, the clinician is involved in rating the characteristics of voice as present at the time of recording. In contrast, the perception of the individual about the impact of the condition on his or her quality of life is influenced by several factors, such as chronicity of the problem or professional voice use. Thus, the perceived voice characteristics and the severity of dysphonia need not always correlate highly with the patient completed self-rating measures. Congruent to the current findings, the GRBAS scale and quality of life measured using Voice Related Quality of Life (V-RQOL) have also been found to have a moderate positive relationship [39]. Studies in the past among individuals who underwent thyroidectomy [40] and multiple sclerosis [41] have also reported similar correlations between VHI and the GRBAS scale.
Weak to moderate correlations were found between the self-rating measure of VHI and the acoustic measures of AVQI and ABI, similar to those reported by Pommȇe et al. [42]. Thus, there is some correlation between the impact of dysphonia on the quality of life reflected as higher scores on VHI and its subsections and the acoustic markers of dysphonia. Furthermore, we did not observe correlations between MPD and any of the VHI scores similar to existing literature [19]. We observed that measures of vocal fatigue and MPD did not correlate well with other measures of voice evaluation. Nevertheless, the findings of this study need to be verified in a larger cohort.
There are a few limitations to this study. Primarily, we did not include objective aerodynamic measures of voice evaluation, such as airflow or air pressure measurements, which are potential contributors to differentiating primary MTD [43]. Hence, future studies can also consider involving objective aerodynamic measures and determine their correlation to other measures of voice evaluation. Similarly, surface electromyography [8] is another possible diagnostic tool for identifying primary MTD, which can be correlated with multiple measures of voice evaluation. Another limitation of this study is that the sample size was not justified statistically. Although consecutive sampling was employed in this study, it is advised that future replications of this study involve a statistically justified sample size.
Conclusion
Literature has frequently upheld the notion that the evaluation of any voice disorder should comprise subjective and objective measures [9, 10, 44, 45]. The use of multiple measures of voice evaluation supplements each other and provides the clinician with comprehensive information on the patient and their medical condition. The findings of the present study reveal that each measure of voice evaluation provides distinct information about the multidimensional nature of dysphonic voice in individuals with MTD. However, there are some correlations between different measures of voice evaluation in individuals with MTD. As revealed by the findings of the current study, multidimensional assessment of voice quality of individuals with MTD provides a better understanding of the condition. The relationships between different dimensions of voice evaluation could aid in an appropriate diagnosis of the condition. An appropriate diagnosis and a multidimensional vocal profiling of muscle tension dysphonia would help practicing Speech-Language Pathologists in therapeutic decision-making, which in turn, can have a positive impact on improving quality of life in individuals with MTD.
Acknowledgements
The authors acknowledge the Director, All India Institute of Speech and Hearing, Mysuru, (a recognized research Centre of University of Mysore) for permitting to carry out this study. Preliminary findings from this study were presented at Fr Muller’s Speech and Hearing Conference (FOCUS-3 Muller’s SHCoN) held from 1st to 2nd December 2023 at the Father Muller College of Speech and Hearing, Mangalore, India.
Author Contributions
Both the authors contributed to the study conception and design. Data collection and analysis were performed by the first author (JJB). The first draft of the manuscript was written by JJB and revised by the second author (TJ). Both the authors have read and approved the final manuscript.
Funding
This research was funded by Junior Research Fellowship awarded to the first author by All India Institute of Speech and Hearing.
Declarations
Ethical Approval
The procedures of this study adhered to ethical regulations set by the institutional ethical committee. We obtained informed consent from all the participants before initiating the procedures of this study. The authors have no ethical conflicts to disclose.
Conflicts of Interest
The authors have no conflicts of interest to declare.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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