Thalamic short pulse stimulation diminishes adverse effects in essential tremor patients

Objective To investigate the effect of directional current steering and short pulse stimulation in the ventral intermediate thalamic nucleus (VIM) on stimulation-induced side effects in patients with essential tremor. Methods We recruited 8 patients with essential tremor in a stable postoperative condition (> 3 months after electrode implantation of deep brain stimulation [DBS] electrodes) with segmented contacts implanted in the VIM. Tremor severity on acute stimulation was assessed by the Fahn-Tolosa-Marin Tremor Rating Scale. Cerebellar impairment was evaluated with the International Cooperative Ataxia Rating Scale. Patients rated paresthesia intensity with a visual analog scale. Results In all patients, tremor was reduced to the same extent by VIM stimulation regardless of pulse width using energy dose-equivalent amplitudes. Short pulse stimulation diminished stimulation-induced ataxia of the upper extremities and paresthesia compared with conventional parameters. Directional steering with monopolar stimulation of single segments successfully suppressed tremor but also induced ataxia. No differences in adverse effects were found between single-segment stimulation conditions. Conclusion These proof-of-principle findings provide evidence that acute short pulse stimulation is superior to directional steering in the subthalamic area to decrease stimulation-induced side effects while preserving tremor suppression effects in patients with tremor. Classification of evidence This study provides Class IV evidence that for patients with tremor with thalamic DBS, acute short pulse stimulation reduces adverse effects, while directional steering does not provide a generalizable benefit regarding adverse effects.