Apomorphine test: a predictor for motor responsiveness to deep brain stimulation of the subthalamic nucleus

The value of the apomorphine test as a predictor of the clinical outcome of deep brain stimulation of the subthalamic nucleus (STN) was evaluated in p atients with advanced idiopathic Parkinson's disease (IPD) or multiple syst em atrophy (MSA). Thirteen IPD patients with severe diurnal fluctuations an d one MSA patient not responding to dopaminergic drugs were assessed with t he Unified Parkinson's Disease Rating Scale (UPDRS) and the timed finger ta pping test (FTT), measured preoperatively on and off apomorphine and postop eratively on and off STN stimulation. UPDRS motor items 20-25 were assessed intraoperatively on and off STN stimulation when the clinically effective target was approached. The motor response to immediate intraoperative and l ong-term STN stimulation was correlated with results of the apomorphine tes t. The response to immediate intraoperative STN stimulation was accurately predicted by apomorphine challenge in all 13 IPD patients. Clinical outcome following long-term STN stimulation was correlated significantly with preo perative changes due to apomorphine measured with the UPDRS motor scores (r = 0.7125, P < 0.01) and FTT (r = 0.9276, P < 0.001). More over, comparison of long-term STN stimulation to preoperative drug treatment displayed a si gnificant reduction in the duration of off-phases and a significant increas e in the duration of on-phases. However, in the single patient with MSA no beneficial response was obtained either to apomorphine or to STN stimulatio n intraoperatively and during the postoperative externalized test period. O ur results indicate that the apomorphine test can predict the outcome of im mediate and long-term STN stimulation and may help in the selection of cand idates for surgery.