Introduction

Essential tremor (ET) is the most common movement disorder, affecting 1% of the population worldwide. There is sound evidence that medically refractory tremor improves with thalamotomy and deep brain stimulation (DBS) targeting the thalamic ventralis intermedius nucleus (VIM). In the last few years, the incisionless technique of magnetic resonance-guided focused ultrasound (MRgFUS) has been demonstrated to be an effective procedure for unilateral thalamotomy,1 with a positive profile with regard to side effects.

The thalamus is involved in cognitive functions such as attention/executive control, memory and language. Focal ablation of the thalamus, even when targeting a sensorimotor region as the VIM, raises question about potential cognitive side effects. After unilateral VIM-DBS in 40 patients with ET, Fields et al 2 showed statistically significant improvements in visuoperceptual function and verbal memory. There was no significant decline in any measure, but four patients with preoperative low verbal fluency showed a further decline. Most studies have shown reduced verbal fluency under active VIM-DBS.2–4 Since focused ultrasound thalamotomy is a less invasive procedure, we hypothesised that the risk of procedure-related cognitive decline is further reduced.