Instability of syllable repetition in Parkinson's disease--influence of levodopa and deep brain stimulation.

The aim of this study was to test the hypothesis of a fundamental impairment of vocal pace performance in Parkinson's disease (PD) based on a syllable repetition paradigm and the influence of levodopa and deep brain stimulation of the subthalamic nucleus (STN-DBS). Twenty-two PD patients under stable dopaminergic medication, 14 patients with STN-DBS, and 30 controls were tested. Participants had to repeat the syllable /pa/ in a steady pace. Percental coefficient of variance (COV) of interval length was measured for the description of pace stability. Patients were tested in the OFF state and again in the ON state after levodopa administration or ongoing STN-DBS. COV was elevated in both PD subgroups. COV was not influenced by levodopa administration but showed a further deterioration under STN-DBS. The impaired syllable repetition capacity shows similarities to the patterns of more complex speech rhythm abnormalities in PD and therefore might share the same pathophysiology.