Clinical pitfalls and serological diagnostics of MuSK myasthenia gravis.
Kwon YN., Woodhall M., Sung J-J., Kim K-K., Lim Y-M., Kim H., Kim J-E., Baek S-H., Kim B-J., Park J-S., Seok HY., Kim D-S., Kwon O., Park KH., Sohn E., Bae JS., Yoon B-N., Kim N-H., Ahn S-W., Choi K., Oh J., Park HJ., Shin KJ., Lee S., Park J., Kim SH., Seok JI., Bae DW., An JY., Joo IS., Choi S-J., Nam T-S., Kim S., Park K-J., Kwon K-H., Waters P., Hong Y-H.
BACKGROUND: We aimed to evaluate the diagnostic accuracy of enzyme-linked immunosorbent assay (ELISA) for anti-muscle specific tyrosine kinase (MuSK) antibody (Ab) in a large cohort of anti-acetylcholine receptor (AChR) Ab-negative generalized myasthenia gravis (MG), and also to investigate clinical contexts for the diagnosis of MuSK MG. METHODS: A retrospective study of 160 patients with a clinical suspicion of AChR Ab-negative generalized MG was performed. The serum samples were tested for anti-clustered AChR Ab by cell-based assay (CBA), anti-MuSK Ab by ELISA, CBA and/or radioimmunoprecipitation assay (RIPA). Clinical data were compared between anti-MuSK Ab-positive MG and double seronegative (AChR and MuSK) MG groups. RESULTS: After excluding non-MG and clustered AChR Ab-positive patients, we identified 89 patients as a cohort of AChR Ab-negative generalized MG. Anti-MuSK Ab was positive by ELISA in 22 (24.7%) patients. While CBA identified five additional anti-MuSK Ab-positive patients, the results of ELISA were mostly consistent with CBA and RIPA with Cohen's kappa of 0.80 and 0.90, respectively (p