Ocular myasthenia gravis with anti-muscle-specific tyrosine kinase antibodies: Two new cases and a systematic literature review

Objective Many myasthenia gravis (MG) patients with anti-muscle-specific tyrosine kinase (MuSK) antibodies have prominent oculobulbar symptoms or weaknesses of the neck and respiratory muscles. An ocular form of MG having anti-MuSK antibodies (MuSK-OMG) is very rare. We review the clinical features of two such cases. Methods We reviewed cases of patients with an ocular form of MG having anti-MuSK antibodies, including two new cases. Results We found seven published cases, plus two cases described in this report. The mean age at onset of these nine patients was 37.0 ± 17.7 years, and the mean disease duration (from ocular MG onset to report) was 47.0 ± 43.1 months. The clinical courses appeared benign, but heterogeneous. Five of the patients responded to pyridstigmine. Four patients received immunotherapy, which resulted in improvement. Our two patients had mild ocular symptoms. One patient was stable with no immunosuppressive treatment, and the other patient was treated with prednisolone and tacrolimus. Conclusions Cases of an ocular form of MG having anti-MuSK antibodies do exist. The benign clinical courses and pharmacological responses to cholinesterase inhibitors imply that the antibodies might have different pathogenicities and specificities from those of MuSK-generalized MG. The presence of anti-MuSK antibodies should therefore be determined in ocular MG patients negative for anti-acetylcholine receptor antibodies.