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Anteroposterior lead positioning contributes to poorer long-term outcomes in deep brain stimulation for essential tremor, study suggests

Tuesday, October 14 2008 | Comments

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What's This? Suboptimal electrode positioning appears to be a significant factor in deteriorating long-term control of essential tremor following deep brain stimulation (DBS) of the thalamus, according to the results of a small, single-center study.

Researchers studied the long-term outcomes of 27 patients (females, n=14; mean age at time of surgery, 67 yrs [range, 35 to 85 yrs]) who initially experienced satisfactory control after undergoing DBS between 2001 and 2006 for the treatment of essential tremor. The primary goal of the study was to assess the factors that contribute to stimulation failure (loss of meaningful tremor relief) and less satisfactory outcomes (leads requiring voltages >3.6 V for effective tumor control).

All of the patients demonstrated significant improvement in the writing and drawing subscales of the Fahn-Tolosa-Marin Tremor Rating Scale (P<.001) for >1 year of follow-up after initial DBS. The mean duration of the follow-up period was 40 months (range, 13 to 66 months).

Tremor control eventually deteriorated in 4 of the 27 patients; 1 of these 4 patients eventually developed resting tremor. The mean time to stimulation failure was 39 months (range, 19 to 58 months). There were no statistical differences between the group that experienced long-term control and the group that experienced failure in terms of age (P=.49), disease duration (P=.23), tremor severity (P=.23), or total time after surgery (P=.44). There was also no significant difference in the number or type of kinesthetic cells activated or in the reduction of tremor with intraoperative stimulation.

The mean lateral lead location from midline was 13.4 mm in the group with continued long-term control and 13.5 mm in the group that lost efficacy (P=.45). Similarly, there was no significant difference between the 2 groups with respect to the mean lateral lead location from the ipsilateral wall of the third ventricle (9.8 mm vs 9.5 mm, respectively; P=.34) or the z coordinate (.05 mm vs 0.0 mm, respectively; P=.47). However, there was a significant difference in the mean anteroposterior lead location (5.9 mm anterior to the posterior commissure in the successful group vs 4.6 mm in the group that lost efficacy; P=.06).

Three of the 4 patients who had stimulation failure had a 1 mm to 2 mm deviation between the electrophysiologically determined target and final lead placement. By comparison, only 2 of the 20 patients in the successful group experienced a similar deviation (P=.018).

In an analysis in which the patients with failure were grouped together with those who required increased voltage to a mean of >3.6 V for tremor control, the researchers found no significant differences between these patients and the group with good outcomes in terms of y and z coordinates (P=.49 and P=.10, respectively) or electrode angle (P=.19 vertical, P=.36 horizontal). However, a significant difference was seen between the 2 groups in the x coordinate expressed as the distance from midline (P=.01), and a trend when expressed as the distance from the wall of the third ventricle (P=.07).

This analysis also showed that leads with continued efficacy tended to be more medial to midline as compared with leads in the patients who had less satisfactory outcomes (12.9 mm vs 14.3 mm).

Further, in the group with suboptimal outcomes, intraoperative fluoroscopy indicated that 5 of the 10 leads demonstrated movement of the DBS electrode. In contrast, only 1 of 20 leads in the patients with good long-term outcomes had moved (P=.005).

The patients with electrodes placed more laterally tended to have suboptimal outcomes following DBS, the authors concluded, noting that even a very slight variation from the intraoperatively determined electrophysiological target may eventually cause stimulation efficacy to deteriorate.

"Long-term stimulation failure in patients with essential tremor remains a significant issue, and further studies are mandated to determine the relative roles of location, disease progression, and tolerance development," they remarked. (Pilitsis JG, et al. J Neurosurg 2008;109:640-646.)

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