Instability of syllable repetition in progressive supranuclear palsy

Dysarthria is a prominent feature of progressive supranuclear palsy (PSP) and consists--amongst other features--of impaired speech fluency. Since in Parkinson's disease (PD) steadiness of syllable repetition in the course of the performance has been shown to be impaired, the aim of the present study was to investigate if measurement of syllable repetition shows similar or even more pronounced abnormalities in PSP. Thirty six patients with the clinical diagnosis of PSP (16 PSP-Richardson syndrome/PSP-RS and 20 PSP-parkinsonism/PSP-P), 60 patients with PD and 32 healthy speakers were tested. Participants had to repeat a single syllable in a self chosen isochronous pace. Percental coefficient of variance (COV) of interval length was measured for description of pace stability throughout the performance. All patients were tested according to Unified Parkinson's Disease Rating Scale (UPDRS III). Patients with PSP were additionally scored according to PSP rating scale (PSPRS). In the PSP group, COV was significantly worse not only when compared with healthy speakers but also when compared with PD patients of similar disease duration and similar global motor impairment. COV showed only a trend to higher values in the subgroup with PSP-RS as compared to PSP-P. In the PSP-P, but not in the PSP-RS subgroup, there was a positive correlation between COV and PSPRS/UPDRS III. PSP patients feature more pronounced difficulties in the steady syllable repetition than patients with PD and healthy controls as a hint for a more profound dysfunction of basal motor speech performance in PSP than in PD.