OBJECTIVE Unilateral Gamma Knife thalamotomy (GKT) is a well-established 
treatment for patients with medically refractory tremor who are not eligible for 
invasive procedures due to increased risk of compications. The purpose of this 
study was to evaluate whether staged bilateral GKT provides benefit with 
acceptable risk to patients suffering from disabling medically refractory 
bilateral tremor. METHODS Eleven patients underwent staged bilateral GKT during 
a 17-year period (1999-2016). Eight patients had essential tremor (ET), 2 had 
Parkinson's disease (PD)-related tremor, and 1 had multiple-sclerosis 
(MS)-related tremor. For the first GKT, a median maximum dose of 140 Gy was 
delivered to the posterior-inferior region of the nucleus ventralis intermedius 
(VIM) through a single isocenter with 4-mm collimators. Patients who benefitted 
from unilateral GKT were eligible for a contralateral GKT 1-2 years later 
(median 22 months). For the second GKT, a median maximum dose of 130 Gy was 
delivered to the opposite VIM nucleus to a single 4-mm isocenter. The 
Fahn-Tolosa-Marin (FTM) clinical tremor rating scale was used to score tremor, 
drawing, and drinking before and after each GKT. The FTM writing score was 
assessed only for the dominant hand before and after the first GKT. The 
Karnofsky Performance Status (KPS) was used to assess quality of life and 
activities of daily living before and after the first and second GKT. RESULTS 
The median time to last follow-up after the first GKT was 35 months (range 11-70 
months). All patients had improvement in at least 1 FTM score after the first 
GKT. Three patients (27.3%) had tremor arrest and complete restoration of 
function (noted via FTM tremor, writing, drawing, and drinking scores equaling 
zero). No patient had tremor recurrence or diminished tremor relief after the 
first GKT. One patient experienced new temporary neurological deficit 
(contralateral lower-extremity hemiparesis) from the first GKT. The median time 
to last follow-up after the second GKT was 12 months (range 2-70 months). Nine 
patients had improvement in at least 1 FTM score after the second GKT. Two 
patients had tremor arrest and complete restoration of function. No patient 
experienced tremor recurrence or diminished tremor relief after the second GKT. 
No patient experienced new neurological or radiological adverse effect from the 
second GKT. Statistically significant improvements were noted in the KPS score 
following the first and second GKT. CONCLUSIONS Staged bilateral GKT provided 
effective relief for medically refractory, disabling, bilateral tremor without 
increased risk of neurological complications. It is an appropriate strategy for 
carefully selected patients with medically refractory bilateral tremor who are 
not eligible for deep brain stimulation.