We present the first case of simultaneous muscle-specific kinase antibody positive myaesthenia gravis and relapsing-remitting multiple sclerosis to be reported in the English literature along with the inherent diagnostic and treatment challenges. There may be an association between myaesthenia and central nervous system demyelination. We identified 72 previously published cases of myaesthenia with central nervous system demyelination. Of 19 cases of myaesthenia with relapsing-remitting multiple sclerosis, nine (47%) were acetylcholine receptor antibody negative, but there were no previously published cases with muscle-specific kinase antibody. Further research is required to clarify this association and optimal treatment in such cases.