Bilateral thalamic stimulation for the treatment of essential tremor

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Abstract
Objective: To determine the safety and efficacy of bilateral thalamic stimulation in the treatment of essential tremor (ET). Methods: Nine ET patients with disabling tremor refractory to pharmacotherapy underwent bilateral staged implants. Tremor was assessed by the Fahn-Tolosa-Marin Tremor Rating Scale at baseline 1 (before first implant), baseline 2 (before second implant), and at 6-month and 1-year follow-up. Blinded evaluations were performed at 3 months. Associated changes in speech were evaluated in six patients. There were seven men and two women with a mean age of 73.8 years. Results: There was a significant improvement in the mean total tremor score from a baseline of 66.1 ± 11.6 to 28.4 ± 12.8 12 months after the second surgery. Similarly, the mean motor tremor subscore was 20.1 ± 5.0 before the first surgery and improved significantly to 14.1 ± 3.6 before the second surgery. Motor tremor scores 6 months after the second surgery (6.0 ± 3.7) and 12 months after the second surgery (7.5 ± 3.9) also improved significantly relative to the preoperative scores. The mean activities of daily living (ADL) subscore at baseline was 18.2 ± 2.9 and improved significantly before the second surgery to 9.0 ± 3.2. These ADL scores further improved 6 months (6.2 ± 5.2) and 12 months (7.9 ± 5.7) following the second surgery, but these gains were not significant. Blinded evaluations also revealed a similar degree of improvement. Complications were noted in five patients: asymptomatic intracranial hematoma (1), postoperative seizures (1), a hematoma over the implanted pulse generator (IPG) (1), lead repositioning (1), and IPG malfunction (1). Adverse effects related to stimulation were mild and resolved with adjustment of the stimulation parameters. Three of the six patients demonstrated worsening of dysarthria with both stimulators on. Conclusions: Bilateral thalamic stimulation is effective in reducing tremor and functional disability in ET; however, dysarthria is a possible complication.