The temporal sequence of myasthenia gravis and neuromyelitis optica spectrum disorder: a case report and systematic review of 74 patients

Background The co-occurrence of myasthenia gravis (MG) and neuromyelitis optica spectrum disorder (NMOSD) is rare, and their temporal sequence and shared pathogenesis remain poorly understood. Methods We present the case of a 43-year-old woman with pre-existing acetylcholine receptor antibody (AChR-Ab) positive ocular MG who developed aquaporin-4 antibody (AQP4-Ab) positive NMOSD. Additionally, we conducted a systematic literature review up to July 2024 to identify similar cases. Results Including the present case, 74 patients were analyzed. The cohort showed a marked female predominance (89.2%). MG onset significantly preceded NMOSD onset in most patients (93.2%), with a younger mean age at onset (28.19 vs. 41.02 years, p < 0.001) and a mean interval of 12.56 years. Among tested patients, AChR-Ab was positive in 90.5% and AQP4-Ab in 73.0%. In our case, administration of the complement C5 inhibitor eculizumab led to marked clinical improvement after failure of high-dose steroid therapy. Conclusion This study suggests a consistent temporal pattern wherein MG predominantly precedes NMOSD, often by years, suggesting a possible shared autoimmune predisposition. The observed response to eculizumab highlights complement pathway inhibition as a potentially effective therapeutic strategy for this complex overlap syndrome, warranting further investigation.