Neuromyelitis optica in patients with myasthenia gravis who underwent thymectomy.

BACKGROUND Myasthenia gravis (MG) and neuromyelitis optica (NMO, also known as Devic disease) are rare autoimmune disorders, with upper-limit prevalence estimates in the general population of 15 per 100,000 and 5 per 100,000, respectively. To our knowledge, an association between these diseases has not been previously reported. OBJECTIVES To describe 4 patients with MG who developed NMO after thymectomy and to analyze possible causes of apparent increased prevalence of NMO among patients with MG. DESIGN Case series. PATIENTS Four patients with MG who underwent thymectomy. INTERVENTIONS None. RESULTS The prevalence of MG within the published cohort of patients with NMO is more than 150 times higher than that in the general population. CONCLUSION Dysregulation of B-cell autoimmunity in myasthenia, possibly exacerbated by loss of control over autoreactive cells as a result of thymectomy, may predispose patients to the development of NMO.