MuSK-Ab positive myasthenia: not always grave.

Antibodies (Abs) to muscle-specific tyrosine kinase (MuSK) are detected in approximately 40% of generalized acetylcholine receptor antibody-negative myasthenia gravis (MG). Anti-MuSK Abs are nearly always associated with generalized symptoms, with prevalent involvement of craniobulbar, cervical and respiratory muscles and with a striking preponderance in women. The typical course of MuSK-MG is acute onset, rapid progression, brittle course in the first years, early respiratory crises and unprovoked relapses in spite of high-dose immunosuppression. Patients often require long-term management with multiple immunosuppressive (IS) agents and many of them remain dependent on IS treatment. The majority of anti-MuSK Abs are of the non-complement-binding IgG4 subclass. We report the case of a Greek female MuSK-MG patient with typical phenotype but clearly atypical clinical course during 12 years of follow-up. The patient received only corticosteroid treatment for one year and showed mild and stable MG symptoms under no treatment for the rest of the observation period, except for postpartum mild and short-lived exacerbation. In mildly symptomatic stable state, anti-MuSK Abs were of the IgG4 subclass and no other immunological peculiarity was detected.