On demand deep brain stimulation for essential tremor: an approach to avoid tolerance?

Background: Deep Brain Stimulation (DBS) of the thalamic nucleus ventralis intermedius (VIM) is an established therapy for essential Tremor (ET), but loss of efficacy due to tolerance may occur (2).

Objective: To evaluate if On Demand DBS of the VIM can avoid tolerance.

Methods: Among 20 patients who obtained DBS were 3 patients with ET who in the past 2 years obtained left hemisphere DBS implants targeting the VIM. These patients were instructed to switch on DBS with a magnet only when using their right hand for motor tasks (e.g. writing, drinking, eating). DBS programming was chosen that allowed the best functional improvement with no side effects. In the follow-up, only stimulation amplitude was increased if necessary. Tremor was evaluated by the Clinical Rating Scale for Tremor (CRST).

Results: After DBS implantation 2 patients had a lesioning effect for a few days. Thereafter in all patients DBS led to tremor suppression of the right arm when stimulation was switched on and tremor returned to preoperative state if DBS was discontinued [tremor of right arm (item no. 5 of CRST) presurgery: 4.7±1.2 /1 year postsurgery DBS-ON: 0.3±0.6 and DBS-OFF: 4.6±1.5]. Patients had DBS switched on around 30% of the day. Stimulation amplitude had to be increased from 1.5±0.5 volts to 1.7±0.6 volts in the first months and remained stable for the follow-up. Functional disability, rated by the score of activities of daily living of the CRST, improved from 13.7±3.5 preoperatively to 0.3±0.6 1 year after surgery.

Conclusion: 1.) Compared to the literature (1, 2) where patients switched off DBS only at night, our patients needed a smaller increase of stimulation amplitude over time (see diagram). This, and the use of DBS only 30% of the day, leads to a significant prolongation of battery lifetime, which makes On Demand DBS a consideration for some ET patients with DBS. 2.) In our small number of patients no tolerance phenomena (e.g. secondary therapy failure, tremorrebound) occurred. To further support the advantages of On Demand DBS, a clinical trial with a larger number of patients is needed.

1. Limousin P. et al. „Multicentre European Study of Thalamic Stimulation in Parkinsonian and Essential Tremor“ JNNP 1999; 66: 289–96

2. Hariz M. et al. „Tolerance and Tremor Rebound following Long-Term Chronic Thalamic Stimulation for Parkinsonian and Essential Tremor“ Stereotact Funct Neurosurg. 1999; 72(2–4): 208–18

Fig. 1: Digram showing stimulation amplitudes in the follow-up as compared with the literature.