This retrospective cohort study investigates a potential association between the incidence of tremor habituation and the use of directional deep brain stimulation leads in patients with essential tremor (ET).

Waning efficacy over time well-described in patients with ET with deep brain stimulation (DBS) of the ventral intermediate (ViM) nucleus of the thalamus. The hypothesized mechanisms of this progressive decline in efficacy include suboptimal lead placement, loss of lesional effect over time, intolerable side effects at effective stimulation intensity, and progressive degeneration of the Purkinje cell layer in the cerebellum. In addition to these factors, clinicians have observed a stimulation-dependent phenomenon known as “tremor habituation.”

We reviewed the medical records of 40 patients with ET with 62 individual DBS leads placed in the ViM. Leads that showed a worsening of tremor control within one month of successful re-programming were classified as “habituating.” We then analyzed the incidence of habituation in patients with directional DBS leads compared to non-directional DBS leads.

In our cohort of 40 patients with ET and 62 total leads, none of the 36 directional leads developed tremor habituation, while six of the 26 total non-directional leads (in four patients) developed habituation. The phi coefficient was -0.39, suggesting a negative association between lead type and incidence of tremor habituation.

Our data suggest a reduced incidence of tremor habituation with directional DBS electrodes. The reasons for this association are outside the scope of this retrospective study, but likely include an underlying anatomic contribution to the phenomenon of habituation. Further analyses focused on the precise lead location and volume of tissue activation of patients with and without tremor habituation would clarify this potential causal link, which may result in new strategies to achieve a more durable therapeutic benefit.