Comparing two deep brain stimulation leads to one in refractory tremor

A sizable proportion of medication refractory tremor patients may not respond satisfactorily to deep brain stimulation (DBS) to the ventralis intermedialis nucleus of the thalamus (Vim). Implanting a second DBS lead ipsilaterally to the first one is thought to be beneficial based on scarce and unblinded data. This article aims to report a double-blind assessment of five patients with a second DBS lead for refractory tremor. Tremor was assessed by two blinded movement disorder specialists using a videotaped tremor rating scale (TRS) evaluation of each patient in four conditions: both leads OFF, Vim ON/2nd lead OFF, Vim OFF/2nd lead ON, and both leads ON. Paired t-test was used to determine if double stimulation was different than stimulation of Vim alone or than stimulation of the 2nd lead alone. Each hypothesis was tested with the total TRS as well as the contralateral upper limb score and the contralateral hemibody score. Tremor was secondary to multiple sclerosis in two patients and to essential tremor in three. The second lead was in the ventralis oralis anterior nucleus of the thalamus in three patients and in the prelemniscal radiations in two patients. There was improvement with the 2nd lead or double ON in four patients compared to stimulating the Vim alone. However, when taken as a group, the results were not statistically significant. These results were constant with the three different ratings used. The lack of overall statistically significant improvement might be secondary to the small size and the heterogeneity of our sample. However, four patients had 17 to 60 % tremor improvement after the implant of the 2nd lead on double-blinded evaluation. We report objective improvement after addition of a second DBS lead in patients with tremor refractory to Vim DBS. Larger studies are needed to confirm these results.