Pilot Study Evaluating Safety of Unilateral Gamma Knife Subthalamotomy for Parkinson's Disease

The goal of the study is to enroll 20 subjects who could benefit from unilateral subthalamotomy due to the presence of unilateral rigidity, tremor, bradykinesia and/or dyskinesias (as opposed to axial symptoms such as walking) but who are suboptimal candidates for deep brain stimulation (DBS) because of advanced age (\>74), medical comorbidities precluding surgery, or patient aversion to DBS, and who show more than 30% improvement in Unified Parkinson's Disease Rating Scale (UPDRS) score in the ON versus OFF medication state. Secondary objectives will focus on the efficacy of Gamma Knife (GK) subthalamotomy for Parkinson's disease (PD), as determined by changes in the patient's clinical status and any improvement following the treatment. A full neurologic exam as well as a screen for depression will be administered at every postoperative visit. The patient's neurologic function will be assessed with a full neurological examination and objectively quantified using the UPDRS focusing on the contralateral side, as well as overall UPDRS. The clinician will complete a Clinical Global Impression (CGI) and Mini-Mental State Examination (MMSE) at each visit to record overall impression of the patient's disease progression and severity, and to evaluate cognitive function. Pre- and post-treatment assessment of the Levodopa Equivalent Daily Dose (LEDD) (quantification of medication regimen in levodopa equivalents) will be obtained and recorded to evaluated the efficacy of gamma knife subthalamotomy (GKS) as a treatment for Parkinson's disease (PD). A Parkinson's Disease Questionnaire-39 (PDQ-39) to determine the patient's independence and quality of life will be filled out at each visit. Finally, the patient will complete a Beck Depression Inventory at each clinic visit to monitor for development or progression of depressive symptoms.