Surgical treatment of myoclonus dystonia syndrome

Myoclonus dystonia (M-D) syndrome is a heritable movement disorder characterized by myoclonic jerks and dystonia primarily of the upper extremities. M-D remains poorly responsive to pharmacological treatment. Emerging reports suggest good response to DBS of the internal globus pallidus (GPi) and ventral intermediate nucleus (VIM) of the thalamus. This study aimed to appraise the value of these two DBS targets by evaluating reports available in the literature. A systematic search of published case reports and case series was performed on Medline and Embase. Responses to DBS were evaluated. Myoclonus was assessed with the Unified Myoclonus Rating Scale (UMRS) and dystonia by the Burke-Fahn-Marsden dystonia rating scale (BFMDRS). The primary outcome of interest was the relative improvements noted with GPi, compared to VIM stimulation. A total of 17 publications yielded 40 unique cases, with mean follow-up of 27.2 months. All patients demonstrated improvements in myoclonus scores, with 93.5% showing at least a 50% improvement in UMRS. The mean improvement in myoclonus scores was 72.6%. In contrast, dystonia scores were improved in 87.9% of patients, with 72.7% reporting at least a 50% improvement in BFMDRS. The mean improvement in dystonia scores was 52.6%. Improvements in myoclonus scores were similar for both GPi (75.7%) and VIM (70.4%; P = 0.27). However, the improvements in dystonia scores were greater with GPi (60.2%), compared to VIM (33.3%; P = 0.03). Although both targets achieve similar improvements in myoclonus, GPi stimulation may be a preferred target because it may achieve greater improvements in dystonia, compared to VIM stimulation.