Effects of DBS on precision grip abnormalities in essential tremor.

Deep brain stimulation (DBS) of the ventrolateral thalamus is a highly effective procedure for the treatment of essential tremor (ET). The regularity of repetitive, self-paced finger tapping is known to be abnormal in patients with ET and improved following DBS. However, the more complex timing that underlies force development in the hands in ET and after DBS has not been evaluated. In this pilot study, we assessed precision grip performance in seven ET subjects before and after 5 months of DBS. Ten healthy controls were also studied. ET subjects showed a significant increase in preload duration (235 +/- 145 vs. 82 +/- 49 ms) and peak negative load (-0.524 +/- 0.35 vs. -0.174 +/- 0.14 N) during grip-lift compared with healthy subjects. No difference in load duration was observed between the groups. Following DBS, the magnitude of the peak negative load was significantly reduced (P = 0.03). In contrast, the duration of the load phase was worsened (non-significant) after DBS. We conclude that defects in the control of distal musculature necessary for establishing a stable grip exist in ET, whereas proximal muscles necessary for object lift-off remain relatively intact. Further, synergy paradigms governing grip-lift coordination may also be impaired. Although DBS is successful in alleviating tremor in ET, it produces only a partial restoration of normal precision grip.

A randomized comparison of thalamic stimulation and lesion on self-paced finger movement in essential tremor.

Deep brain stimulation (DBS) and ablation (thalamotomy) of the motor thalamus reduce tremor and improve function of the contralateral hand in patients with essential tremor (ET). Neuroimaging and electrophysiological evidence suggest that unlike a focal lesion, high frequency stimulation affects widespread neural networks that include those involved in motor timing. The purpose of this pilot study was to compare the effects of thalamic stimulation and lesion on the timing of simple, self-paced finger movements in patients with ET. Twenty-one subjects with advanced ET were randomized to unilateral thalamotomy or DBS. Nine healthy controls were also enrolled. Index finger tapping was performed on both hands before and 6 months after surgery. Prior to surgery, timing of simple, repetitive index finger taps was abnormal in both TH and DBS subjects on the contralateral hand. After surgery, regularity was improved by both stimulation and thalamotomy with significantly more improvement in the TH group. On the ipsilateral (non-targeted) hand, timing of index finger taps was improved by stimulation. These results suggest that temporal processing is differentially affected by stimulating and lesioning thalamocortical fibers. That timing regularity is improved ipsilateral to the stimulated thalamus provides evidence that DBS influences a widespread neural network involved in timing of simple repetitive movements.