Long term follow-up of deep brain stimulation of the caudal zona incerta for essential tremor

Purpose The ventral intermediate nucleus of thalamus is the standard target for deep brain stimulation (DBS) in essential tremor (ET). However, favourable data have recently highlighted the caudal zona incerta (cZi) as an alternative target. Reports concerning the long-term results are however lacking, and we have therefore evaluated the long-term effects in our patients with ET and cZi DBS. Methods 18 patients were evaluated using the Essential Tremor Rating Scale (ETRS) before and on-/off-stimulation at 1 and 3-5 years after surgery (mean 48.5+/-10.6 months). Two patients were operated on bilaterally but all electrodes were evaluated separately. The stimulation parameters were recorded and the stimulation strength calculated. Results A baseline total ETRS mean score of 46.0 decreased to 21.9 (52.4%) at the final evaluation. On the treated side, tremor of the upper extremity (item 5 or 6) improved from 6.1 to 0.5 (91.8%) and hand function (items 11-14) improved from 9.3 to 2.0 (78.0%). Activities of daily living improved by 65.8%. There was no increase in stimulation strength over time. Conclusion cZi DBS is a safe and effective treatment for the long term suppression of ET.