A pilot study: Microlesion effects and tremor outcome in the ventrointermediate deep brain stimulation (VIM-DBS)

Objectives: To perform a pilot study to investigate the relationship between the microlesion effect (MLE) seen in deep brain stimulation (DBS) of the ventralis intermedius nucleus (VIM) and subsequent tremor response and DBS parameter settings. Patients and methods: Nineteen thalami in 12 patients (11 essential tremor and 1 Parkinson's disease), who underwent unilateral (n = 5) and bilateral VIM-DBS (n = 7) were assessed at pre- and 24-h post-operation, at their initial DBS activation, and at 6-month follow-up. The severity of tremor was rated (from 0 to 4) for each activity including hand at rest, outstretched, wing beating, finger-nose-finger, dot approximation and spiral drawing (total score ranging from 0 to 24). The difference of total tremor score before and 24-h after electrode implants (MLE) was segregated into 3 groups based on immediate (24 h) post-operative tremor improvement: (1) minimal (none or mild, 0-2), (2) moderate (>2-4), and (3) marked (>4). At the initial activation (23.4 ± 3.7 days post-operation), the mean OFF tremor scores were still marginally better in marked than the minimal and moderate MLE groups. Results: At 6 months, 14 of 19 thalami (74%) were eligible for follow-up analysis. The "OFF" stimulation MLE disappeared in all groups. There was no significant difference of mean ON tremor scores among the groups; however, DBS parameter settings, including amplitude and pulse width, trended to be mildly lower in those with a marked MLE. Conclusion: MLE has minimal long term clinical effect except for possibly allowing for lower DBS settings.