AChR-myasthenia gravis switching to double-seropositive several years after the onset.

We report an early onset AChR-myasthenia gravis (MG) with biphasic clinical course. The clinical "switch" from AChR-MG to MuSK-MG emerged 16 years after the onset and 11 years after thymectomy. MuSK antibodies were detected only by cell-based assay and only upon clinical "switch", while AChR antibodies remained positive and at high titers during the whole disease course. Although the occurrence of AChR antibodies and MuSK antibodies in the same individual is rare, the re-assessment of the antibody status, using all available assays, is advisable when there is clinical indication.