ANTI-MuSK ANTIBODY MYASTHENIA GRAVIS: CLINICAL FINDINGS AND RESPONSE TO TREATMENT IN TWO LARGE COHORTS

Introduction: Myasthenia gravis (MG) patients with autoantibodies to muscle-specific tyrosine kinase (MuSK) represent a distinct subset of those with this disease. Treatment and outcomes data in these patients are limited and conflicting. Methods: We reviewed 110 MuSK-MG patients from two large clinics in Italy and the USA. Results: Thirty-nine to 49% of patients with generalized, acetylcholine receptor antibody (AChR-Ab)-negative MG had MuSK-MG. Eighty-five percent were female, with disease onset typically in the fourth decade. Ocular and/or bulbar symptoms were present at onset in 79% of those studied. Eighty-five percent were MGFA class III or greater, and crisis occurred in 28%. Plasma exchange (PLEX) produced improvement in 93%, whereas only 61% improved after intravenous immunoglobulin. Long-term outcomes were comparable to those of patients with AChR-Ab-positive MG. Conclusions: MuSK-MG has a marked female predominance with frequent oculobulbar weakness and crises. Many patients deteriorate rapidly early in the disease, and PLEX is usually the preferred treatment. Long-term outcomes are similar to those of patients with AChR-Ab_MG. Muscle Nerve 44:36-40, 2011