OBJECTIVE Multiple sclerosis (MS) is a neurodegenerative disease that can lead 
to severe intention tremor in some patients. In several case reports, 
conventional radiotherapy has been reported to possibly exacerbate MS. 
Radiosurgery dramatically limits normal tissue irradiation to potentially avoid 
such a problem. Gamma Knife thalamotomy (GKT) has been established as a 
minimally invasive technique that is effective in treating essential tremor and 
Parkinson's disease-related tremor. The goal in this study was to analyze the 
outcomes of GKT in patients suffering from medically refractory MS-related 
tremor. METHODS The authors retrospectively studied the outcomes of 15 patients 
(mean age 46.5 years) who had undergone GKT over a 15-year period (1998-2012). 
Fourteen patients underwent GKT at a median maximum dose of 140 Gy (range 
130-150 Gy) using a single 4-mm isocenter. One patient underwent GKT at a dose 
of 140 Gy delivered via two 4-mm isocenters (3 mm apart). The posteroinferior 
region of the nucleus ventralis intermedius (VIM) was the target for all GKTs. 
The Fahn-Tolosa-Marin clinical tremor rating scale was used to evaluate tremor, 
handwriting, drawing, and drinking. The median time to the last follow-up was 39 
months. RESULTS After GKT, 13 patients experienced tremor improvement on the 
side contralateral to surgery. Four patients noted tremor arrest at a median of 
4.5 months post-GKT. Seven patients had excellent tremor improvement and 6 had 
good tremor improvement. Four patients noted excellent functional improvement, 8 
noted good functional improvement, and 1 noted satisfactory functional 
improvement. Three patients experienced diminished tremor relief at a median of 
18 months after radiosurgery. Two patients experienced temporary adverse 
radiation effects. Another patient developed a large thalamic cyst 60 months 
after GKT, which was successfully managed with Ommaya reservoir placement. 
CONCLUSIONS Gamma Knife thalamotomy was found to be a minimally invasive and 
beneficial procedure for medically refractory MS tremor.