Effect of termination of subthalamic stimulation on upper limb bradykinesia in Parkinson's disease

Background: Deep brain stimulation (DBS) of the subthalamic nucleus is an effective treatment for motor symptoms in advanced Parkinson's disease (PD). To determine the optimal stimulation site, multiple locations are stimulated and the clinical effect is registered. These tests require knowledge of the time characteristics of the stimulation effect. The aim of this study was to establish the time course of bradykinesia after the termination of DBS. Methods: Nine patients with chronically implanted bilateral DBS participated. Two repetitive movements were investigated: a finger-tapping task and a forearm pronation-supination task. Movements were recorded by ultrasonic technology. Subjects were instructed to perform the required movements as fast as possible and with the largest amplitude. The trials involved the repetition of 4 seconds of active movement followed by a 6-s pause. This cycle was repeated for 5min. Results: When DBS was switched off, the amplitude and velocity of the investigated movements significantly declined, but their frequency did not. The time course of this decline was modeled by an exponential function, which yielded time constants between 15 and 30s. The effect of stimulation had completely disappeared within 1 minute. Conclusions: These results suggest that it is best to wait at least 1 minute after the end of stimulation before further assessments. Moreover, evaluations based on movement frequency give inconsistent and thus unreliable findings. (P.V. was supported by an ENS Fellowship for 2005 and Z.K by an EU Marie-Curie Training Fellowship)