Deep brain stimulation of the subthalamic nucleus in Parkinson's disease: effects of variation in stimulation parameters

Objective-To investigate the relation between the variation of the paramete rs of stimulation and the clinical effectiveness in parkinsonian patients t reated with deep brain stimulation of the subthalamic nucleus (STN), to pro vide information on the electrical parameter setting and the mechanism of a ction of deep brain stimulation. Methods-Ten patients with Parkinson's disease bilaterally implanted in the STN were studied. For every patient the intensity of the stimulus necessary to obtain the disappearance of contralateral wrist rigidity (required clin ical effect, RCE) and the side effect threshold in 20 different conditions of stimulation, coupling four pulse width values (60, 120, 210, 450 Its) wi th five rate values (10, 50, 90, 130, 170 Hz) were determined. All the pati ents were tested after a 12 hour withdrawal of antiparkinsonian drugs, and the clinical evaluation was double blind. Results-In all the patients it was impossible to obtain the RCE using 10 an d 50 Hz stimulus rates. For all the other stimulus rate values, the intensi ty-pulse width curves (IPWCs) for the RCE and for the side effect threshold showed a hyperbolic trend. For every pulse width value, increasing the rat e from 90 to 130 and to 170 Hz progressively decreased the intensity of the stimulus necessary to reach the RCE, but the differences were not signific ant. Within the same rate value, the progressive reduction of the stimulus intensity necessary to obtain the RCE, obtained with the lengthening of the pulse width was significant (p <0.05) only comparing 60 with 210 ps and 60 with 450 ps. Conclusions-The findings give some useful indications for the electrical pa rameter setting in deep brain stimulation of the STN, and some information about the mechanism of action of deep brain stimulation.