'Asleep' deep brain stimulation targeting ventral intermediate thalamus in essential tremor: systematic review.

Introduction: Deep brain stimulation (DBS) of the ventral intermediate thalamus (VIM) is a safe and effective treatment of essential tremor (ET). Traditionally microelectrode recording (MER) was used to confirm lead placement in the target structure in the awake state. More recently, lead placement using indirect anatomical targeting with the patient under general anaesthesia has been described and implemented in many centres, and is referred to as 'asleep DBS'. We performed a systematic review of asleep DBS procedures for ET to assess the outcomes of this technique.

Methods: A systematic review was performed looking at all studies utilising asleep DBS for ET according to PRISMA guidelines. PubMed, Web of Science and Cochrane database were searched. Only studies in ET with a VIM target were included.

Results: 229 patients with 406 leads inserted asleep across 9 studies were included with robotic and non-robotic guided insertion. 3 studies had an internal comparison with traditional awake methods with microelectrode recordings (132 patients with 214 leads). Functional improvement ranged from 48% to 71% [weighted mean (wm) 57.62%]. Radial errors across the studies ranged between 0.5 and 1.9 mm (wm 0.83 mm). The percentage of leads passed successfully on first pass ranged from 88.3% to 100%. Complication rates ranged from 0% to 41.7% (wm 7.45%), with haemorrhage rates ranging from 0% to 8.3% (wm 2.19%), infections 0-16.2% (wm 1.89%) and altered mental status from 0% to 24.2% (wm 0.67%). Mean total operative room times ranged from 205 to 333 minutes for bilateral lead insertion only. Mean length of stay ranged from 1.5 to 3 days.

Conclusion: Asleep DBS, targeting VIM, is a safe and effective procedure in the treatment of essential tremor. High levels of precision allow submillimetre target accuracy in many cases. Functional outcomes and complications are comparable to awake procedures performed with MER. Larger randomised control trials directly comparing asleep to awake procedures with MER are desirable.