Background Pace and rhythm of speech and non-speech vocal utterances have recently been shown to be impaired in speakers with manifest HD. These findings have been interpreted as dysfunctions of timing and maintaining of basic motor speech programs as a consequence of disruption of basal ganglia circuitries in HD. However, nothing is known about motor speech performance in the premanifest stages of HD so far.
Aim The aim of the study was to survey if there are characteristic patterns of abnormalities of speech and non-speech vocal performance in speakers with premanifest Huntington´s disease (HD).
Methods We examined 28 speakers with premanifest HD and 32 age-matched control persons using a speech task consisting of a) reading a German text (for the calculation of net speech rate/ NSR and pause ratio/ PR%) and b) several subtests for the monitoring of non-speech vocal performance to calculate the maximum syllable repetition capacity/ maxSylRep and the precision of syllable in a self-chosen steady pace (the coefficient of variance/COV displayed the steadiness of repetition).
Results Speakers with premanifest HD showed a significantly higher velocity of reading (elevated NSR) with reduced speech pauses. Furthermore, maxSylRep was significantly higher (5.43 Hz ± 1.21 vs. 3.73 Hz ± 1.33, p < 0.0001), but steadiness of syllable repetition was worse (1.61 ± 0.54 vs. 1.00 ± 0.28, p < 0.0001) in the HD group as compared to control speakers. NSR and maxSylRep were closely correlated to clinical parameters as overall motor impairment and the cognitive score, to the CAG index and the estimated years of disease onset and the MRI-based calculation of the caudate nucleus volume.
Conclusions Abnormalities of speech rate and rhythm are detectable even in the premanifest stages of HD. Interestingly, velocity of reading and syllable repetition have been found to be higher than in control speakers whereas measures of steadiness of repetition were worse. Further longitudinal studies are warranted to survey the evolution of these distinctive patterns with time which might be helpful for the monitoring of disease progression and could provide some further insight into the underlying pathophysiology of HD.