Gamma Knife thalamotomy for essential tremor.

OBJECTIVES: The purpose of this study was to evaluate the results following Gamma Knife thalamotomy (GKT) for medically refractory essential tremor in a series of patients in whom open surgical techniques were not desirable.
METHODS: Thirty-one patients underwent GKT for disabling essential tremor after medical therapy had failed. Their mean age was 77 years. Most patients were elderly or had concomitant medical illnesses. A single 4-mm isocenter was used to target a maximum dose of 130 or 140 Gy to the nucleus ventralis intermedius. Items from the Fahn-Tolosa-Marin clinical tremor rating scale were used to grade tremor and handwriting before and after radiosurgery.
RESULTS: The median follow-up was 36 months. In the group of 26 evaluable patients, the mean tremor score (+/- standard deviation) was 3.7 +/- 0.1 preoperatively and 1.7 +/- 0.3 after radiosurgery (p < 0.000015). The mean handwriting score was 2.8 +/- 0.2 before GKT and 1.7 +/- 0.2 afterward (p < 0.0002). After radiosurgery, 18 patients (69%) showed improvement in both action tremor and writing scores, 6 (23%) only in action tremor scores, and 3 (12%) in neither tremor nor writing. Permanent mild right hemiparesis and speech impairment developed in 1 patient 6 months after radiosurgery. Another patient had transient mild right hemiparesis and dysphagia.
CONCLUSIONS: Gamma Knife thalamotomy is a safe and effective therapy for medically refractory essential tremor. Its use is especially valuable for patients ineligible for radiofrequency thalamotomy or deep brain stimulation. Patients must be counseled on potential complications, including the low probability of a delayed neurological deficit.