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.