10 Years Follow-Up of Deep Brain Stimulation in the Caudal Zona Incerta/Posterior Subthalamic Area for Essential Tremor.

Background: Long-term data on the effects of deep brain stimulation (DBS) for essential tremor (ET) is scarce, especially regarding DBS in the caudal Zona incerta (cZi) and the posterior subthalamic area (PSA).

Objectives: The aim of this prospective study was to evaluate the effect of cZi/PSA DBS in ET at 10 years after surgery.

Methods: Thirty-four patients were included. All patients received cZi/PSA DBS (5 bilateral/29 unilateral) and were evaluated at regular intervals using the essential tremor rating scale (ETRS).

Results: One year after surgery, there was a 66.4% improvement of total ETRS and 70.7% improvement of tremor (items 1-9) compared with the preoperative baseline. Ten years after surgery, 14 patients had died and 3 were lost to follow-up. In the remaining 17 patients, a significant improvement was maintained (50.8% for total ETRS and 55.8% for tremor items). On the treated side the scores of hand function (items 11-14) had improved by 82.6% at 1 year after surgery, and by 66.1% after 10 years. Since off-stimulation scores did not differ between year 1 and 10, this 20% deterioration of on-DBS scores was interpreted as a habituation. There was no significant increase in stimulation parameters beyond the first year.

Conclusions: This 10 year follow up study, found cZi/PSA DBS for ET to be a safe procedure with a mostly retained effect on tremor, compared to 1 year after surgery, and in the absence of increase in stimulation parameters. The modest deterioration of effect of DBS on tremor was interpreted as habituation.