Instability of syllable repetition as a marker of disease progression in Parkinson's disease: a longitudinal study.

Parkinsonian speakers show a tendency to articulatory acceleration and have difficulties to keep the steady pace of repeated syllables. The aim of this study was to analyse the stability of motor speech performance based upon a syllable repetition paradigm during the course of disease to find a potential marker of disease progression in Parkinson's disease (PD). 58 patients with PD and 35 controls were tested and re-tested after at least 12 months (mean: 33.40/range: 12-88). In the PD group, motor impairment was similar at first and second visit. Participants had to repeat the syllable /pa/ in a self chosen steady pace. Percental coefficient of variance (COV) of interval length was measured for description of pace stability throughout the performance. Percental pace acceleration (%PA) was based upon a comparison of the speed of syllable repetition in the first and second half of the task. Patients with PD showed a significant elevation of COV and %PA indicating an instability of syllable repetition and a tendency to pace acceleration in the course of performing. Furthermore, in the PD group, COV and %PA showed a significant deterioration from first to second examination. Instability of steady syllable repetition in PD shows characteristic changes during the course of the disease, but no correlation with general motor impairment. Therefore, the underlying mechanism may be independent from dopaminergic deficits. The potential role of impaired syllable repetition as a marker of non-dopaminergic disease progression in PD needs validation by further studies.