PSA and VIM DBS efficiency in essential tremor depends on distance to the dentatorubrothalamic tract

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.