Thalamic deep brain stimulation for essential tremor: Recommendations for long-term outcome analysis

Objectives: Determine the efficacy of thalamic deep brain stimulation (DBS) for tremor control among individuals with essential tremor (ET). Methods: A clinical series of 52 consecutive individuals undergoing placement of a DBS system for treatment of ET completed an unblinded battery of subjective and objective measures at postoperative intervals of one, three, and 12 months, and 14 annually thereafter up to three years. The assessment battery included measures of tremor and activities of daily living. Results: Both subjective and objective measures showed that stimulation was associated with significant improvement at nearly every postoperative interval as compared to pre-operative and stimulation 'off' ratings of activities of daily living functioning, midline tremor, contralateral upper extremity tremor, and contralateral lower extremity tremor. Ipsilateral tremor showed some improvement with stimulation, but only within the first three months. Trend analysis showed stable tremor control. Stimulation settings remained largely unchanged after the first three months. Dysarthria was more common among those with bilateral stimulation. A range of missing data estimation methods were performed, and subsequent analyses corroborated the main findings of the study. Conclusion: Thalamic DBS is generally a well-tolerated and effective treatment for ET. Methodological and analytical recommendations are provided for the evaluation of long-term outcome.