Japanese cases of neuromyelitis optica spectrum disorder associated with myasthenia gravis and a review of the literature.

BACKGROUND: The incidence of concurrent myasthenia gravis (MG) and neuromyelitis optica spectrum disorder (NMOSD) is higher than what chance predicts, yet it remains unclear why MG and NMOSD appear concurrently.

OBJECTIVE: The purpose of the present study was to examine the clinical features of the concurrence of these diseases.

METHODS: Clinical details were analyzed retrospectively.

RESULTS: Three (0.5%) out of 631 MG patients had confirmed (n=2) or suspected (n=1) NMOSD. Two of these patients were women. All showed early-onset MG (EOMG) that preceded NMOSD and were positive for acetylcholine receptor antibody (AChR-Ab). Two patients were tested for aquaporin 4 antibody (AQP4-Ab) and were positive. Two patients were treated with a thymectomy that preceded NMOSD. Two patients had decreased frequency of regulatory T (Treg) cells. We identified in the literature 46 patients with both MG and NMOSD. Our results of female predominance, EOMG, MG preceding NMOSD, and positive AChR-Ab are consistent with previous descriptions.

CONCLUSIONS: This is the first report to examine the frequency of NMOSD in Japanese patients with MG. The reduction and/or dysfunction of Treg cells may be one cause of NMOSD development in MG.