OBJECT: In published series of patients who undergo deep brain stimulation (DBS) of the thalamus the effects of unilateral stimulation on contralateral limb tremor have been reported. The authors detail their experience with bilateral thalamic DBS in the treatment of head, voice, and bilateral limb tremor and compare it with earlier studies of unilateral stimulation. METHODS: Twenty-three patients (six with Parkinson's disease, 15 with essential tremor, and two with multiple sclerosis) underwent 19 bilateral DBS procedures (nine staged, 10 simultaneous) and four procedures contralateral to thalamotomy to control tremor of the head in 10, voice in seven, and limbs in 20 patients. Limb tremor improvement was graded as follows: 4, no tremor; 3, stress-induced tremor; 2, functional improvement; 1, no functional improvement; and 0, persistent tremor. Improvement of head or voice tremor was graded as follows: 4, greater than 75%; 3, between 50% and 75%; 2, between 25% and 50%; 1, less than 25%; and 0, no improvement. The mean follow-up period was 10 months. Twenty-two patients (96%) demonstrated improved tremor at the last follow-up review. Of 20 patients with bilateral limb tremor, 17 (85%) improved to Grades 3 and 4, two patients (10%) with multiple sclerosis improved to Grade 2, and one (5%) exhibited tremor recurrence 8 months later. Nine (90%) of 10 patients with severe head tremor improved to Grades 4 or 3. Six (86%) of seven patients with voice tremor improved to Grade 3. Seven patients (30%) developed dysarthria, and seven (30%) developed disequilibrium; symptoms reversed in the majority of patients after the stimulation parameters were changed. One patient (4%) developed mild memory decline. There were no deaths. CONCLUSIONS: The following findings are reported: 1) bilateral thalamic DBS and stimulation contralateral to thalamotomy are safe; 2) staging the procedure does not reduce the risk of dysarthria or gait disequilibrium; and 3) head and voice tremor are primary indications for bilateral DBS.
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