Seronegative myasthenia and myasthenia gravis with anti-MuSK antibody: A retrospective study of 20 cases

Introduction. - Despite the fact that anti-muscle specific tyrosine kinase (MUSK) antibodies have been discovered for seven years, only a few studies have, until now, focused on myasthenia without acetylcholine-receptors antibodies (ab) (formerly known as "seronegative myasthenia"), and among them, anti-MuSK-antibody-positive and -negative patients. Method. - We retrospectively studied 20 patients with "seronegative" myasthenia gravis, eight of them being anti-MuSK-ab positive, the remaining twelve being negative. We searched for clinical, neurophysiological, and therapeutic differences between the two groups (anti-MuSK-ab positive: anti-MuSK+ versus anti-MuSK-ab negative: anti-MuSK-). Results. - Anti-MuSK+ patients had more predominantly bulbar involvement and had more severe disease (these patients required referral to intensive care more frequently). There was no difference between the two groups concerning treatment efficiency and tolerance. Most of our patients were treated with acetylcholinesterase-inhibitors, and immunomodulatory or immunosuppressive drugs that could indirectly reflect greater severity. However, there was no difference in treatments for anti-MuSK+ versus anti-MuSK-patients. Conclusion. - These results both confirm and complete the preexisting data on RACh-negative myasthenia, and especially on myasthenia associated with MuSK antibodies. (C) 2009 Elsevier Masson SAS. All rights reserved.