Autoantibody detection by a live cell-based assay in conventionally antibody-tested triple seronegative Myasthenia gravis.

Autoantibody testing is the mainstay in confirming the diagnosis of autoimmune myasthenia gravis (MG). However, in approximately 15% of patients, antibody testing in clinical routine remains negative (seronegative MG). This study aimed at assessing the prevalence of "clustered" AChR- and MuSK- and LRP4- autoantibodies using a live cell-based assay in a large German cohort of seronegative myasthenia gravis (SNMG) patients. A total of 67 SNMG patients were included. Clustered AChR-ab were identified in 4.5% (n = 3) of patients. Two out of the three patients showed binding to the adult AchR as well as the fetal AchR. None of the patients was positive for MuSK- or LRP4-autoantibodies. There were no differences in clinical characteristics between the patients with and without clustered AChR-ab detection. Comparison of clinical data of our cohort with clinical data from the nationwide Myasthenia gravis registry showed broad similarities between seronegative MG patients of both cohorts.