AChR myasthenia gravis switching to MuSK or double antibody positive myasthenia gravis in two children and literature review.

Muscle-specific tyrosine kinase antibody (MuSK-Ab) and acetylcholine receptor antibody (AChR-Ab) coexistence in myasthenia gravis (MG) is very rare. In this report, two children with AChR-Ab switching to double antibody positive MG (DP-MG) or MuSK-Ab positive MG (MuSK-MG) are described. Six similar cases were found in the literature via online database search. Therefore, this study describes eight patients in total, six female and two male. The average age of onset was 7.25 ± 5.95 years. Four AChR-MG patients switched to DP-MG with no known precipitating factor and four switched after thymectomy (two to MuSK-MG and two to DP-MG). After the serological switch, the patients transitioned to the phenotype of MuSK-MG and responded poorly to cholinesterase inhibitors and well to corticosteroids and plasma exchange.