Objective To compare directional monopolar, bipolar, and directional bipolar thalamic deep brain stimulation (DBS) in tremor patients. Methods Fourteen tremor patients (7 Essential Tremor and 7 Parkinson's Disease) implanted with directional DBS electrodes in the ventral intermediate nucleus (VIM) were enrolled. Side‐effect thresholds of monopolar directional stimulation (DIRECT) were compared to circular DBS as well as, in a randomized design, to those of two different bipolar stimulation settings (BIPOLAR = circular anode; BI‐DIRECT = directional anode). Tremor suppression (Tremor Rating Scale, TRS) right below the side‐effect threshold was also assessed. Results Directional DBS in the individually best direction showed higher side‐effect thresholds than circular DBS (p = 0.0063). The thresholds were raised further using either one of the bipolar stimulation paradigms (BIPOLAR p = 0.0029, BI‐DIRECT p = 0.0022). The side‐effect thresholds did not differ between both bipolar settings, but side‐effects were less frequent with BI‐DIRECT. No difference in TRS scores with stimulation just below the side‐effect threshold was found between all stimulation conditions. Conclusions Side‐effect thresholds of monopolar directional and bipolar stimulation with both circular and directional anodes were higher compared to traditional monopolar circular stimulation in the VIM. Bipolar DBS with directional anodes evoked side‐effect less frequently than bipolar and monopolar directional stimulation. All stimulation settings had comparable effects on tremor suppression just below their side‐effect thresholds. Thus, directional and different bipolar settings should be explored in patients with bothersome side‐effects of thalamic stimulation when monopolar stimulation settings are not satisfying. Further studies are needed to explore the efficiency of the different bipolar stimulation paradigms.

The new essential tremor (ET) classification defined ET-plus (ET-p) as an ET subgroup with additional neurological signs besides action tremor. While deep brain stimulation (DBS) is effective in ET, there are no studies specifically addressing DBS effects in ET-p. 44 patients with medication-refractory ET and thalamic/subthalamic DBS implanted at our center were postoperatively classified into ET and ET-p according to preoperative documentation. Tremor suppression with DBS (stimulation ON vs. preoperative baseline and vs. stimulation OFF), measured via the Fahn–Tolosa–Marin tremor rating scale (TRS), stimulation parameters, and the location of active contacts were compared between patients classified as ET and ET-p. TRS scores at baseline were higher in ET-p. ET-p patients showed comparable tremor reduction as patients with ET, albeit higher stimulation parameters were needed in ET-p. Active electrode contacts were located more dorsally in ET-p of uncertain reason. Our data show that DBS is similarly effective in ET-p compared to ET. TRS scores were higher in ET-p preoperatively, and higher stimulation parameters were needed for tremor reduction compared to ET. The latter may be related to a more dorsal location of active electrode contacts in the ET-p group of this cohort. Prospective studies are warranted to investigate DBS in ET-p further.

Postoperative choice of the most effective deep brain stimulation (DBS) contact in patients with essential tremor (ET) so far relies on lengthy clinical testing. Previous studies showed that the postoperative effectiveness of DBS contacts depends on the distance to the dentatorubrothalamic tract (DRTT). Here, we investigated whether the most effective DBS contact could be determined from calculating stimulation overlap with the individual DRTT. Seven ET patients with bilateral thalamic deep brain stimulation were included retrospectively. Tremor control was assessed for each contact during test stimulation with 2mA. Individual DRTTs were identified from diffusion tensor imaging and contacts were ranked by their stimulation overlap with the respective DRTT in relation to their clinical effectiveness. A linear mixed-effects model was calculated to determine the influence of the DRTT overlap on tremor control. In all investigated DBS leads, the contact with the best clinical effect was the contact with the highest or second-highest DRTT overlap. At the group level, the DRTT-overlap explained 26.7% of the variance in the clinical outcomes (p < 0.001). Our data suggest that the overlap with the DRTT based on individual tractography may serve as a marker to determine the most effective DBS contact in ET patients and reduce burdensome clinical testing in the future.

Objective: To investigate the relation between deep brain stimulation (DBS) of the posterior-subthalamic-area (PSA) and the ventral-intermediate-nucleus (VIM) and the distance to the dentatorubrothalamic tract (DRTT) in essential tremor (ET). Methods: Tremor rating scale (TRS) hemi-scores were analyzed in 13 ET patients, stimulated in both the VIM and the PSA in a randomized, crossover trial. Distances of PSA and VIM contacts to population-based DRTTs were calculated. The relationships between distance to DRTT and stimulation amplitude, as well as DBS efficiency (TRS improvement per amplitude) were investigated. Results: PSA contacts were closer to the DRTT (p=0.019) and led to a greater improvement in TRS hemi-scores (p=0.005) than VIM contacts. Proximity to the DRTT was related to lower amplitudes (p<0.001) and higher DBS efficiency (p=0.017). Conclusions: Differences in tremor outcome and stimulation parameters between contacts in the PSA and the VIM can be explained by their different distance to the DRTT.