Improvement of Isolated Myoclonus Phenotype in Myoclonus Dystonia after Pallidal Deep Brain Stimulation

BACKGROUND: Myoclonus–dystonia is a condition that manifests predominantly as myoclonic jerks with focal dystonia. It is genetically heterogeneous with most mutations in the epsilon sarcoglycan gene (SGCE). In medically refractory cases, deep brain stimulation (DBS) has been shown to provide marked sustainable clinical improvement, especially in SGCE-positive patients. We present two patients with myoclonus–dystonia (one SGCE positive and the other SGCE negative) who have the isolated myoclonus phenotype and had DBS leads implanted in the bilateral globus pallidus internus (GPi). METHODS: We review their longitudinal Unified Myoclonus Rating Scale scores along with their DBS programming parameters and compare them with published cases in the literature. RESULTS: Both patients demonstrated complete amelioration of all aspects of myoclonus within 6–12 months after surgery. The patient with the SGCE-negative mutation responded just as well as the patient who was SGCE positive. High-frequency stimulation (130 Hz) with amplitudes greater than 2.5 V provided therapeutic benefit. DISCUSSION: This case series demonstrates that high frequency GPi-DBS is effective in treating isolated myoclonus in myoclonus–dystonia, regardless of the presence of SGCE mutation.