Differential diagnosis of muscle tension dysphonia and spasmodic dysphonia
Muscle tension dysphonia (MTD) can mimic the voice features of adductor spasmodic dysphonia (ADSD) leading to diagnostic confusion. Researchers have begun to compare characteristics of MTD and ADSD to determine whether there are markers which reliably distinguish the two disorders and lead to improved differential diagnosis. Differences between MTD and ADSD have been identified during fiberoptic laryngoscopy, phonatory airflow measurement, acoustic analysis, and variable sign expression based upon phonatory task. In general, evidence of task-dependent sign expression and intraword phonatory breaks should raise suspicion of ADSD over MTD. However, on the basis of conventional standards of diagnostic precision, no single diagnostic test currently exists that reliably distinguishes the two disorders. Although perceptual voice evaluation remains the standard for differential diagnosis of ADSD and MTD, knowledge of factors that influence the severity of sign expression in ADSD is important to differential diagnosis. During clinical assessment, voice clinicians who use generic stimulus materials that do not control for specific phonetic environments or voice tasks may miss critical phenomenological features of ADSD.