Clinical pitfalls and serological diagnostics of MuSK myasthenia gravis

Young Nam Kwon, Mark Woodhall, Jung Joon Sung, Kwang Kuk Kim, Young Min Lim, Hyunjin Kim, Jee Eun Kim, Seol Hee Baek, Byung Jo Kim, Jin Sung Park, Hung Youl Seok, Dae Seong Kim, Ohyun Kwon, Kee Hong Park, Eunhee Sohn, Jong Seok Bae, Byung Nam Yoon, Nam Hee Kim, Suk Won Ahn, Kyomin ChoiJeeyoung Oh, Hyung Jun Park, Kyong Jin Shin, Sanggon Lee, Jinseok Park, Seung Hyun Kim, Jung Im Seok, Dae Woong Bae, Jae Young An, In Soo Joo, Seok Jin Choi, Tai Seung Nam, Sunyoung Kim, Ki Jong Park, Ki Han Kwon, Patrick Waters, Yoon Ho Hong

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


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 < 0.001). The most frequent differential diagnosis was motor neuron disease particularly of bulbar onset which showed remarkably overlapping clinical and electrophysiological features with MuSK MG at presentation. Conclusion: While confirming the highest sensitivity of CBA for detecting anti-MuSK Ab, our results highlight the clinical pitfalls in making a diagnosis of MuSK MG and may support a diagnostic utility of MuSK-ELISA in clinical practice.

Original languageEnglish
Pages (from-to)1478-1486
Number of pages9
JournalJournal of Neurology
Issue number3
StatePublished - Mar 2023

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© 2022, The Author(s).


  • Anti-MuSK antibody
  • Cell-based assay
  • Radioimmunoprecipitation assay
  • Seronegative myasthenia gravis


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