Perceptual and Acoustical Features of Dysarthria in Essential Tremor: An Observational Study that Expands the Cerebellar Features of Essential Tremor.

Background: Clinical, neuroimaging and postmortem studies indicate cerebellar dysfunction in essential tremor (ET). Clinically this is reflected in intention tremor, gait ataxia, and impaired motor timing. However, the effect of cerebellar dysfunction on speech in ET remains unclear, and research on dysarthria in ET is limited. This study aimed to 1) identify the perceptual features of dysarthria in ET, 2) verify the prominent perceptual features using acoustical analyses, and 3) determine the percentage of participants exhibiting hyperkinetic, ataxic or mixed hyperkinetic-ataxic dysarthria. Methods: Speech samples from fifteen participants with ET were analyzed. An expert rater completed auditory-perceptual ratings, and acoustical analyses were completed that corresponded to perceptual features detected in participants' speech, including speech timing, prosody, and voice quality measures. Results: Perceptual analyses revealed slow and variable speech rate, prolonged interword intervals and phonemes, imprecise consonants, distorted vowels, hypernasality, vocal tremor, harshness, breathiness, hoarseness, reduced loudness, and excess loudness variation in more than 50% of the participants. Acoustical analyses confirmed the presence of vocal tremor as well as numerically lower articulation rate, longer and more variable syllable duration, and lower smoothed cepstral peak prominence in more than 50% of participants compared to normative data from prior studies. Acoustical analyses classified one participant as ataxic and 14 participants as mixed hyperkinetic-ataxic. Discussion: This study revealed the presence of cerebellar signs of dysarthria in speakers with ET, primarily supporting a mixed hyperkinetic-ataxic dysarthria profile in ET. The data indicate that cerebellar dysfunction in ET does not spare speech and voice.