The purpose of this paper is to review the methods used for the assessment of muscular tension dysphonia (MTD). The MTD is a functional voice disorder associated with abnormal laryngeal muscle activity. Various assessment methods are available in the literature to evaluate the laryngeal hyperfunction. The case history, laryngoscopy, and palpation are clinical methods for the assessment of patients with MTD. Radiography and surface electromyography (EMG) are objective methods to provide physiological information about MTD. Recent studies show that surface EMG can be an effective tool for assessing muscular tension in MTD.
Muscular tension dysphonia (MTD) is a common functional dysphonia manifested by excessive tension in the intrinsic and/or extrinsic (para) laryngeal muscles. Approximately 10–40% of the clients at a voice clinic have MTD [
The pathophysiology of MTD is not fully understood [
The assessment of extrinsic laryngeal muscular tension is important for the diagnosis of voice disorders [
Assessment methods of MTD can be classified into two distinct groups: (1) noninstrumental methods, which do not need any equipment for examination (e.g., case history, palpation); (2) instrumental methods, which use tools for objective diagnosis of conditions and include observation, radiography, and electromyography.
Case history is a routine and simple clinical method to assess muscular tension in patients with MTD. Patients are usually asked for vocal misuse/abuse and influences of the stress or psychological factors on voice [
Palpation of neck is a routine procedure for the evaluation of muscular tension around the larynx [
Observation of larynx and vocal folds is a critical part of voice examination. There are some criteria that can be used as the primary diagnostic indicators in MTD. The key features of MTD include posterior glottal chink, mucosal vocal folds changes, suprahyoid muscle tension, hard glottal attack, and larynx rise [
A recent investigation by stepp et al. questioned the use of some measures such as the estimates of AP supraglottal compression, quantitative measures of AP, and false vocal fold (FVF) supraglottal compression [
Radiography can be used for differential diagnosis of MTD. In a study to determine whether radiographic measures for patients with primary MTD were different from those of normal subjects, Lowell et al. (2012) studied 10 patients with primary MTD and 10 normal subjects radiographically while producing phonation. They reported higher positions of the hyoid and larynx during phonation in MTD patients compared with normal subjects. This study indicates that radiographic measures targeting hyoid and larynx can be used in delimitation of pathologic patterns in MTD during phonation [
Electromyography (EMG) of the larynx is a standard test to evaluate the integrity of muscular and nervous system of larynx thorough recording action potentials generated in the muscle fibers. The EMG technique may use needle or surface electrode for recording muscle activity. The needle EMG is an invasive technique in which electrodes are inserted into the target muscles. This procedure can be used reliably in diagnosis of voice problems associated with neurological or neuromuscular conditions [
The surface EMG (sEMG) is used to record muscle activation using surface electrodes. As reported in the literature, sEMG can be used as an objective measure for diagnosis or outcome assessment in MTD [
Several investigations have been performed to determine the vocal hyperfunction behaviors in vocal fold paralysis, MTD, and vocal fold nodules using sEMG [
Many factors should be taken into consideration when using sEMG for measurement of laryngeal hyperfunctional behaviors. These factors can be classified into vocal tasks, participant’ characteristics, and factors affecting EMG recording outcomes. Speech tasks of connected speech or reading can distinguish patients with MTD from subjects without MTD compared with tests at rest or phonation tasks. The tension during connected speech changes quickly and flexibly, and it is restricted in the presence of tension [
Summaries of studies using surface electromyography.
Authors | Design | Participants | Tasks | Type of electrodes | Electrode |
Outcome measure | Results |
---|---|---|---|---|---|---|---|
Redenbaugh and Reich 1989 [ |
Case-control | 7 normal and |
At rest, phonation, and reading |
Unipolar | Thyrohyoid membrane | RMS | (i) EMG levels in MTD significantly higher than normal |
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Hočevar-Boltežar et al. 1998 [ |
Case-control | 5 normal and |
At rest, |
Unipolar | Perioral area and |
RMS | (i) Increases of EMG activity in the perioral and supralaryngeal muscles before and during phonation |
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Stepp et al. 2010 [ |
Pretest-posttest | 13 patients with |
Phonation, |
Double-differential | (1) Thyrohyoid, omohyoid, and sternohyoid |
RMS | (i) No significant reductions in RMS after injection |
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Stepp et al. 2011 [ |
Case-control | 10 normal and |
Phonation, |
Double-differential | (1) Thyrohyoid, omohyoid, and sternohyoid |
RMS | (i) No significant difference between groups |
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Stepp et al. 2011 [ |
Pretest-posttest | 16 patients with vocal hyperfunction |
Phonation, |
Double-differential | (1) Thyrohyoid, omohyoid, and sternohyoid |
RMS | (i) No reliably changes over one session voice therapy |
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Van Houtte et al. 2013 [ |
Case-control | 44 normal and |
At rest, |
Bipolar | (1) Mylohyoid, geniohyoid, and digastric |
RMS | (i) Not able to discriminate between MTD and normal subjects |
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Stepp et al. 2010 [ |
Case-control | 18 normal and 18 patients with vocal nodules | Reading, |
Double-differential | (1) Thyrohyoid, omohyoid, and sternohyoid |
NIBcoh | Significant decrease in NIBcoh in patients compared to healthy speakers |
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Stepp et al. 2011 [ |
Repeated measures | 10 normal | Reading, |
Double-differential | (1) Thyrohyoid, omohyoid, and sternohyoid |
NIBcoh | Significant reduction of NIBcoh during mimicking hyperfunctional voice |
RMS: root mean squared; MTD: muscle tension dysphonia; EMG: electromyograghy; sEMG: surface electromyograghy; SCM: sternocleidomastoid; NIBcoh: neck intermuscular beta coherence.
One important factor which should be kept in mind when using sEMG to quantify neck muscle tension is the variability due to the electrode contact and neck musculature of the subjects. Normalization procedure against a reference contraction can be considered as a way to overcome this problem but it is a difficult task in the assessment of speech muscles. Problems with amplitude normalization have led the researchers to suggest intermuscular coherence as a method to obtain reliable data when assessing vocal hyperfunction [
Recently, sEMG was measured from two electrodes on the anterior neck surface of 18 subjects with vocal nodules and 18 subjects with normal voice to explore the intermuscular coherence in the beta band as a possible indicator of vocal hyperfunction. Coherence was calculated from sEMG data while subjects produced both read and spontaneous speech. The speech type had no significant effect on average coherence, and the mean coherence in the beta band was significantly lower than that in control group. Authors concluded that the EMG beta coherence in neck strap muscle during speech production can be an indicator of vocal hyperfunction [
Various assessment methods (clinical, radiological, and electromyography) have been used to measure laryngeal muscular tension in patients with MTD. The commonly used methods for evaluation and diagnosis of MTD are clinical, which includes case history, observational techniques, and palpation. The radiography as well as the sEMG can be used as objective measures for differential diagnosis of MTD. The evaluation of muscle activity using sEMG provides a measure to quantitatively obtain neurophysiological data in assessing MTD. Surface EMG with intermuscular beta coherence at frequency range of 15–35 Hz could be used to assess vocal hyperfunction. The researchers could use sEMG as a means to investigate the underlying physiological mechanisms involved in MTD.
The authors thank Dr. Stepp for her valuable and useful comments on the paper.