Two-year follow-up of chronic stimulation of the posterior subthalamic white matter for tremor-dominant Parkinson's disease

OBJECTIVE: To determine the efficacy and safety of unilateral deep brain stimulation on the posterior subthalamic white matter, including the zona incerta (ZI) and the prelemniscal radiation (PRL), for tremor-dominant parkinsonian patients. and to determine the exact location of electrodes that were most effective. METHODS: Eight parkinsonian patients with severe resting tremor underwent unilateral stimulation of the ZI/PRL by use of stereotactic guidance. Electrophysiological targeting was obtained by macrostimulation and by somatosensory evoked potentials recorded directly through a quadripolar deep brain stimulation lead. Postoperative computed tomographic scans and magnetic resonance images were performed to confirm anatomic location of the electrode. Parkinsonian motor disabilities were evaluated by use of the Unified Parkinson's Disease Rating Scale in the medication-off. state before surgery and every 6 months after electrode implantations. RESULTS: The mean location of the clinically effective contacts was in the posterior, subthalamic white matter, including the ZI and the PRL (mean, 5.6 +/- 11.2 mm posterior to the midcommissural point, 3.2 +/- 1.1 mm inferior to the anterior commissure-posterior commissure line, and 10.5 +/- 1.2 mm lateral to the midline). At 24 months after operation, ZI/PRL stimulation resulted in significant improvement in mean Unified Parkinson's Disease Rating Scale motor score by 44.3%, contralateral tremor by 78.3%, contralateral rigidity by 92.7%, and contralateral akinesia by 65.7% above the "off-stimulation" scores. Handwriting, posture, and gait were also improved. There were no or only mild adverse events. CONCLUSION: Unilateral ZI/PRL stimulation is a reliable and long-term therapeutic modality and can be considered another surgical target for the treatment of tremor-dominant Parkinson's, disease.