Neuromyelitis optica also known as Devic’s disease is an uncommon, immune mediated demyelinating condition of the central nervous system affecting predominantly the spinal cord and optic nerves. Since 1894 when Eugene Devic summarised 17 known cases of optic neuritis and myelitis the relation between neuromyelitis optica and multiple sclerosis (MS) has been controversial. The overlapping clinical features and the propensity for patients with neuromyelitis optica to express a range of auto-antibodies can result in misdiagnosis, of both MS and other autoimmune disorders. However, clinical, radiological, and immunopathological studies suggest neuromyelitis optica is distinct from MS. The recent identification of an apparent disease specific antibody—termed NMO-IgG (against the aquaporin-4 water channel) implicates humoral immunity.^2,3 This further differentiates the disorder from MS and suggests that treatment to prevent relapses should be aimed primarily at humoral B cell mediated immunity if a pathogenic role for NMO-IgG is confirmed.