Relationship of Stimulation Site Location within the Subthalamic Nucleus Region to Clinical Effects on Parkinsonian Symptoms

OBJECTIVE: To determine the relationship of the stimulation site in the subthalamic region to the clinical effects on parkinsonian symptoms, the monopolar stimulation of 4 electrode contacts and the resulting effects on parkinsonian symptoms were evaluated. METHODS: Seventeen consecutive patients (3 males and 14 females) were enrolled in the study. The patients were evaluated while in a nonmedicated state, and 10-20 min after switching on the pulse generator the effects of stimulation were assessed using separate-subset Unified Parkinson's Disease Rating Scale scores. RESULTS: The relationship between the site stimulated and the percent improvement was analyzed using polynomial regression. Rigidity (p = 0.0004, R2 = 0.15), akinesia (p = 0.02, R2 = 0.07) and total score (p = 0.009, R2 = 0.089) well fit to second-order polynomial regression and showed the greatest improvement after stimulation at 0-1 mm below the horizontal anterior-posterior commissure (AC-PC) plane. Tremor (p = 0.24, R2 = 0.18) and gait (p = 0.36, R2 = 0.001) had a weak relation to the site stimulated, but stimulation at the sites 0-1 mm below the AC-PC plane also produced greater improvement than stimulation at more ventral or dorsal sites. The percent improvement of the posture (p = 0.92, R2 = 0.002) had no relation to the site stimulated. The dorsal border of the subthalamic nucleus was located 0.6 +/- 1.2 mm (n = 27) below the AC-PC plane and the most effective electrode contact 1.2 +/- 1.3 mm (n = 27) below it. CONCLUSIONS: Stimulation around the dorsal border of the subthalamic nucleus, close to the AC-PC plane, produces greater improvement of parkinsonian symptoms than stimulation at more ventral or dorsal sites.