Neuromyelitis optica spectrum disorders (NMOSD), previously known as Devic disease or neuromyelitis optica (NMO), are inflammatory conditions resulting in severe demyelination of the central nervous system (CNS). Classic symptoms include optic neuritis (often bilateral) and transverse myelitis with extremity weakness, sensory loss, and sphincter dysfunction. Brain stem syndromes, such as narcolepsy or area postrema syndrome with intractable nausea, vomiting, and hiccups, can also occur. NMOSD has been associated with other autoimmune disorders including Sjögren syndrome, systemic lupus erythematosus, myasthenia gravis, ulcerative colitis, autoimmune thyroid disease, and autoimmune liver disease.

NMOSD is associated with disease-specific antibodies including aquaporin (AQP)-4-immunoglobulin G (IgG) and, less commonly, anti-myelin oligodendrocyte glycoprotein (MOG) antibodies. Thought to be mediated by the humoral immune system, NMOSD has a relapsing course, with months to years between attacks, and disability is based on accumulation of deficits from attacks. Incidence is up to 10 times higher in women than men, with onset typically in the third to fourth decade, although the disease can be seen in children and older adults. NMOSD is more prevalent in those of African, East Asian, and Latin American descent than in those of Northern European descent.

Prognosis is variable and depends on the number and severity of attacks, although rates of disability and mortality are high.