Objective: To determine the incidence of loss of tremor control in essential tremor (ET) patients who have undergone ventralis intermedius thalamic nucleus deep brain stimulation (VIM DBS).

Background: VIM DBS has been shown to be safe and effective in treating ET for patients whose tremor does not respond adequately to pharmacologic intervention. It is the standard of care for patients with medically refractory tremor but there is growing recognition that a certain subset of patients has waning of benefit over time. The definition for waning of benefit is variable in the literature and thus it is difficult to educate patients on clinically meaningful expectations. Prior work has proposed a clinically applicable definition of waning of benefit that includes the need for reprogramming DBS in order to control tremor.

Methods: A retrospective chart review was performed on all patients who had undergone VIM DBS for ET at our institution during 2009-10. Subjects were deemed to have had waning of benefit if they required two consecutive visits where DBS parameters were adjusted in an effort to control tremor. The number of months from surgery to time of second consecutive reprogramming visit was recorded. The duration of follow-up was also recorded for those who did not meet our criteria for waning of benefit. Other parameters such as age, gender, disease duration and number of internal pulse generator replacements were recorded.

Results: There were a total of 17 patients included, 9 females, with mean age of 68.2 (SD 7.0) and mean disease duration of 18.8 years (SD 14.4) at time of VIM DBS surgery. The number of subjects with waning of benefit was 11 out of 17, or 64.7%. Of these 11 subjects, the mean time to waning of benefit was 26.6 months. The mean number of internal pulse generator replacements for patients with waning of benefit was 1.4 versus 0.3 in patients without waning of benefit and this difference was found to be marginally significant (t=2.23, p=0.042).

Conclusions: This data indicates that in our population there was waning of benefit from VIM DBS in controlling ET in 64.7% of patients. Patients with waning required more battery changes (1.4 versus 0.3) during duration of follow-up indicating that those with waning of benefit required settings that drained the battery at a faster rate. We plan to investigate strategies for avoiding tolerance and thus prolong benefit of DBS for ET in future studies.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/incidence-of-waning-tremor-control-in-essential-tremor-patients-with-deep-brain-stimulation/