Test Details: Neuromyelitis optica (NMO) is a severe relapsing inflammatory demyelinating disease of the CNS that preferentially affects the optic nerve, spinal cord and circumventricular organ systems. Antibodies to aquaporin‐4 (called NMO‐IgG or AQP4‐Ab) in CSF sample is a marker for diagnosis of neuromyelitis optica (NMO) that can facilitate the differential diagnosis of NMO and classic multiple sclerosis.