MuSK-antibody positive myasthenia gravis: clinical and electrodiagnostic patterns.

OBJECTIVE: To examine the clinical manifestations and patterns of electromyographic abnormalities in MuSK-Ab positive myasthenia gravis. METHODS: The clinical evaluations and electrodiagnostic testing results of 20 MuSK-Ab positive myasthenia gravis patients were retrospectively reviewed and compared with matched AChR-Ab positive (N = 72) and MuSK-Ab negative/AChR-Ab negative (N = 24) patients. RESULTS: MuSK-Ab positive patients were younger and more frequently female and African-American, and compared to the AChR-Ab positive patients, were more likely to present with respiratory symptoms or neck extension weakness. MuSK-Ab positive patients were less likely to have abnormal jitter in a limb muscle: only 59% had abnormal jitter in the extensor digitorum communis muscle, compared to 80% of the AChR-Ab negative/MuSK-negative patients and 91% of the AChR-Ab positive patients. CONCLUSIONS: Our MuSK-Ab positive patients not only differ demographically from our MuSK-Ab negative cohort, but they also appear to have a more limited distribution of SFEMG abnormalities. SIGNIFICANCE: The possibility that electrophysiologic abnormalities may not be widely distributed should be considered during electrodiagnostic evaluation of suspected MuSK-Ab positive MG and in selecting muscles for molecular, morphologic, or microphysiologic studies in this condition.

Duke Scholars

Author Janice Munn Massey Neurology, Neuromuscular Disease

Author Donald Benjamin Sanders Neurology, Neuromuscular Disease