gms | German Medical Science

Objective: Some patients with thalamic deep brain stimulation (DBS) for essential tremor (ET) experience habituation of tremor-reduction. After every readjustment of the simulation parameters the tremor initially improves, but is recurring within days or weeks. The ventralis intermedius nucleus (Vim) is the current main target side for ET in DBS. However, the dentato-rubro-thalamic tract (DRTT) is discussed in the literature to be the relevant structure to stimulate. The goal of our study was to investigate the distance from the active contact of the DBS electrode to the DRTT and compare this distance between good responders and patients with habituation of tremor reduction.

Method: In this retrospective study we performed deterministic fiber tracking of the DRTT in 6 patients (12 hemispheres) with ET who underwent DBS in the Vim. Regions of interest were defined in the cerebellar dentate nucleus, the superior cerebellar peduncle and the contralateral red nucleus. Subsequently we measured the distance between the active contact of the electrode and the DRTT in both hemispheres. The clinical tremor response of those 6 patients was analyzed accordingly.

Results: The distance between the active contact and the DRTT in patients with better and constant clinical tremor-reduction was shorter (mean distance: 2,9 ± 2.2 mm standard deviation) than in patients that showed habituation of their response (mean distance: 6.1 ± 3.9 mm standard deviation) One patient with unsatisfying tremor-reduction after habituation of stimulation has obtained revision of the thalamic electrode with adjustment of the electrode placement inside the DRTT. During the 3 month follow-up, tremor alleviation was significant and persistent.

Conclusions: In patients with excellent and persistent tremor alleviation the active contact of the electrodes was located closer to the DRTT than in patients who experienced habituation to the stimulation leading to recurrent tremor.