MuSK autoantibodies in myasthenia gravis detected by cell based assay--A multinational study.

Seronegative myasthenia gravis (MG) presents a serious gap in MG diagnosis and understanding. We applied a cell based assay (CBA) for the detection of muscle specific kinase (MuSK) antibodies undetectable by radioimmunoassay. We tested 633 triple-seronegative MG patients' sera from 13 countries, detecting 13% as positive.

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.