Unilateral Left Deep Brain Stimulation of the Caudal Zona Incerta Is Equally Effective on Voice Tremor as Bilateral Stimulation: Evidence from 7 Patients with Essential Tremor.

BACKGROUND/AIMS: Deep brain stimulation (DBS) is less effective on voice tremor than arm tremor, and it is generally assumed that successful voice tremor treatment requires bilateral DBS and possibly more precise thalamic stimulation. However, recent findings suggest that these assumptions should be reconsidered.

OBJECTIVES: To evaluate whether unilateral DBS targeting the caudal zona incerta (cZi) may be sufficient to alleviate voice tremor in patients with essential tremor, or whether bilateral stimulation is needed.

METHODS: Seven patients with voice tremor off stimulation were evaluated during bilateral stimulation using their clinical settings, and during unilateral left stimulation in iterations with increasing stimulation amplitude. Two expert listeners assessed voice tremor severity in all samples in a blinded procedure.

RESULTS: Six patients had comparable or better effects with unilateral left stimulation compared to bilateral stimulation. For the seventh patient, unilateral DBS at a slightly higher amplitude achieved similar results as bilateral DBS. Overall, high-amplitude stimulation did not appear to be beneficial on voice tremor.

CONCLUSIONS: Unilateral left and bilateral cZi-DBS had comparable effects on voice tremor in the investigated group of 7 patients. This finding suggests that the assumption that bilateral DBS is required to treat voice tremor may need to be reconsidered.