Investigators at the University of Oxford, UK and 8 other international neurology centers describe the clinical, serological, and temporal associations of myasthenia gravis (MG) and neuromyelitis optica spectrum disorder (NMOSD) in 16 patients. All had early onset acetylcholine receptor antibody [AChR-Ab]-mediated MG, the majority with mild generalized disease, and a high proportion achieved remission. The MG preceded NMOSD by a median of 16 years, and 11 had thymectomy. Aquaporin-4 antibodies [AQP4-Ab] were detectable between 4 and 16 years prior to NMOSD onset. AChR-Abs decreased and the AQP4-Ab levels increased over time in concordance with MG and NMOSD, respectively. AChR-Abs were detectable at NMOSD onset in one of 2 patients diagnosed with NMOSD before MG. 
COMMENT. The association of MG and NMOSD, 2 rare organ-specific autoimmune diseases mediated by 2 distinct antibodies, occurs more frequently than by chance. MG usually presents first, and respective antibodies are present years before onset of the relevant disease. The MG tends to be relatively mild and treatment responsive. Recent evidence suggests that the thymus is involved in both MG and NMOSD . Given the risk of concurrent autoimmune diseases in patients with MG or NMO, routine evaluation of thyroid antibodies and AQP4-Abs may be considered in patients with early onset AChR-MG.