Objective: To report the outcomes of a series of isolated dystonia patients with prominent tremor treated with thalamic deep brain stimulation (DBS).

Background: Pallidal and subthalamic nucleus DBS has been shown to be effective in various forms of dystonia. However, dystonia is a heterogeneous group of disorders and the ideal brain target for each dystonia phenotype is still unknown. Recently the thalamus, especially the ventral intermediate nucleus (Vim), has gained interest as a target for dystonic tremor syndromes given its efficacy in treating essential and parkinsonian tremor.

Methods: Six cases were identified from a retrospective review on all cases of isolated dystonia treated with Vim DBS at University of California, San Francisco, and San Francisco Veterans Affairs Medical Center. One patient had dystonic head tremor, 2 patients had dystonic head tremor with hand tremor, 2 patients had bilateral hand tremor with spasmodic dysphonia, and 1 patient had asymmetric and positional hand tremor. Patient demographics, Fahn-Tolosa-Marin Tremor Rating Scale (TRS) and the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) scores at baseline and last follow-up, lead locations, stimulation settings, and side effects were recorded. All patients had Vim implantation with contact zero placed at or within 2 mm below the intercommissural plane.

Results: Median follow-up interval was 6.8 months (range 2-84). Hand tremor (n=5) improved by 74% (range 63-98) in the total TRS score and 72% (range 62-98) in the TRS motor subscore. Dystonic head tremor (n=3), improved by 68% (range 45-81) in the total TWSTRS score and 30% (range 9-50) in the TWSTRS severity subscore. Of the 11 DBS leads, 3 were in monopolar configuration, 7 in bipolar, and 1 in double monopolar. The middle two contacts were most frequently used (75%). Six leads were programmed with constant current (mean=3.2 mA, range 1.0-5.0) and 5 with constant voltage (mean=2.9 V, range 2.3-3.3). Mean pulse width and frequency were 82 microsec (range 60-110) and 155 Hz (range 130-180), respectively. Two patients had paresthesia and dysarthria that improved in bipolar configuration. One patient had appendicular and gait ataxia that improved with bipolar configuration and higher frequency and pulse width.

Conclusions: Vim DBS can be an effective treatment for isolated dystonia with prominent tremor, improving both the motor symptoms and the associated pain and disability.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effect-of-thalamic-deep-brain-stimulation-in-isolated-dystonia-associated-with-prominent-tremor/