Effects of low-frequency thalamic deep brain stimulation in essential tremor patients

Abstract

Background: Essential tremor (ET) patients may present with postural and/or intentional tremor. But despite high-frequency thalamic deep brain stimulation (DBS) effectively suppressing both, the emergence of intentional tremor has been attributed to a higher extent to cerebellar dysfunction. Therefore, we hypothesized thalamic 10 Hz-stimulation, which is known to worsen motor functions, having more impact on intentional tremor than on postural tremor.

Methods: In sixteen ET-patients with bilateral thalamic-DBS, tremor rating scale (TRS) and ultrasound-based tremor-amplitude measurements were analyzed by sequentially applying three DBS-settings in a randomized order: i) low-frequency stimulation (LFS), ii) DBS being turned off (DBS-OFF) and iii) high-frequency stimulation (HFS). Repeated measures analyses of variance for TRS and for the quotients of tremor-amplitudes during DBS-OFF and LFS for intentional (q(int)) and postural tasks (q(post)) were calculated. Finally, electrode localization and the abovementioned quotients were put into relation by Pearson's correlation coefficient.

Results: HFS reduced TRS significantly compared to DBS-OFF and LFS (ps<.001), while the latter two also differed significantly with TRS being the worst during LFS (p<.05). Additionally, intentional tremor-amplitude appeared to be strongly influenced by LFS than postural tremor-amplitude (p<.05). Furthermore, a lower placement of the electrodes caused worse intentional tremor-amplitude during LFS (r=.517, p>.05), while postural tremor-amplitude was unrelated to electrode localization (ps<.05).

Conclusions: During LFS in ET-patients, there is a more severe exacerbation of intentional tremor compared to postural tremor. Possibly, there are two different mechanisms responsible for both tremor entities, making more refined stimulation regimes feasible in the future.

Keywords: Deep brain stimulation; Essential tremor; Intentional tremor; Postural tremor; Subthalamic white matter; Thalamus.