Gamma knife thalamotomy for Parkinson's tremor: A 5-year experience

Purpose: Elderly, high-risk surgical patients, may be unfit for radiofrequency thalamotomy for Parkinson's tremor. We have performed gamma knife radiosurgery in this select patient population, in lieu of open surgery, in an attempt at amelioration of disabling tremor. Materials and Methods: Radiosurgical nucleus ventralis intermedalis thalamotomy using gamma unit technique was performed on 38 patients (median age, 72 years; range: 50-88 years) over a period of 5 years. A median dose of 155 Gy (range: 110-160 Gy) was delivered using a single 4-mm collimator to 40 nuclei (2 patients underwent bilateral thalamotomy) using only anatomical atlas landmarks. The number of males and females were evenly divided, and their ages ranged from 50 to 88 years (median: 72 years). Two-thirds of the patients underwent left thalamotomy for right-sided trmor. Patients were followed-up for a median of 14 months (range: 6 to 43 months). Independent neurological evaluation of tremor as well as subjective patient evaluation were based on a 4-tiered scale: no improvement, mild improvement (0-33% effect), good improvement (33-66% effect), and excellent improvement (66-100%). Results: Eight thalamotomies (20%) failed, four (10%) gave mild improvement, and 28 (70%) gave good to excellent improvement of tremor (median time of onset of improvement was 3 months; range: 1-11 months). In 12 patients (32%) the tremor was eliminated completely. Concordance between independent neurologist evaluation and that of the patient was significant (p<0.001). Two patients in the failure group had an initial transient improvement. Two patients who underwent unilateral thalamotomy had bilateral improvement of their tremor. A permanent 5-6 mm lesion was seen on all follow-up MRIs and there were no radiological complications. A worsening of hand strength was seen in only patient. Conclusion: The safety and efficacy of gamma unit radiosurgical thalamotomy is on par with that of radiofrequency thalamotomy, and in a select surgical high-risk patient population, it may be the treatment choice