Mapping stimulation-induced beneficial and adverse effects in the subthalamic area of essential tremor patients

Abstract Background Stimulation of the subthalamic area (STA) is an effective treatment in essential tremor patients, but limited by stimulation induced adverse effects. The aim of this study was to determine the spatial distribution of stimulus related tremor suppression, ataxia induction and paresthesia of the upper limb in the subthalamic area (STA) of essential tremor patients. Methods We recruited eight patients with essential tremor in a stable postoperative condition (>3 months after surgery). Stimulation-induced effects were assessed with suprathreshold stimulation. Tremor severity was assessed with the Fahn-Tolosa-Marin tremor rating scale (TRS) and cerebellar impairment was evaluated using the international cooperative ataxia rating scale (ICARS). Patients rated paresthesia intensity with a visual analog scale. Linear regression analysis was performed to associate stereotactic coordinates with tremor, ataxia and paresthesia. Results Suprathreshold stimulation significantly decreased tremor and elicited ataxia and paresthesia in all patients ( P P P  = 0.07), i.e. inferior stimulation sites elicit stronger ataxia. Furthermore, paresthesia was positively correlated with y-coordinates (r = 0.66; P P  = 0.08), i.e. posterior and lateral stimulation sites within the STA caused more paresthesia. Conclusion Antero-dorso-medial stimulation site in the STA were associated with less tremor and adverse effects in our small single-center cohort of ET patients with thalamic DBS.