Neuromyelitis optica: clinical syndrome and the NMO-IgG autoantibody marker

Neuromyelitis optica (NMO) is a severe demyelinating disease of the CNS that preferentially affects the optic nerves and spinal cord, tends to relapse, and results in early permanent disability for most affected patients. A new autoantibody marker called neuromyelitis optica immunoglobulin G (NMO-IgG), which targets the water channel protein aquaporin-4, is highly specific for NMO. The marker has demonstrated that the NMO spectrum of disorders is wider than previously known and includes some patients with single-episode or recurrent longitudinally extensive myelitis, recurrent isolated optic neuritis, Asian optic-spinal multiple sclerosis, and patients with co-existing systemic autoimmune diseases such as lupus erythematosus or Sjögren's syndrome. We review the place of NMO within the nosology of CNS demyelinating diseases, the discovery of NMO-IgG and its impact on the definition of NMO and its spectrum, implications for understanding NMO pathogenesis, and informing treatment decisions.