Movement characteristics in Parkinson's disease: determination of dopaminergic responsiveness and threshold.

We evaluated the responsiveness of tap rate (TR), movement time (MT), and reaction time (RT) to intravenous (i.v.) (n = 10) and subcutaneous (s.c.) (n = 16) administration of apomorphine in patients with Parkinson's disease (PD). In the second part of this study, we evaluated the feasibility of the commonly used 15% TR threshold, above which a patient is considered to be a responder. Compared to MT, TR emerged as the most responsive measure of bradykinesia during both i.v. and s.c. administration of apomorphine. RT showed no response to dopaminergic stimulation. To evaluate the influence of threshold on the number of responsive sessions, we determined the baseline variability of TR by means of the coefficient of variation (CV) in 39 patients with PD. Our results show approximately similar numbers of responsive sessions using the 15% and 2CV threshold. Our findings suggest that a simple repetitive motor task--TR--is more responsive than is the MT task. Finally, the 15% threshold may be considered an adequate threshold for TR in assessment of dopaminergic responsiveness of bradykinesia.