Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune condition that affects the central nervous system, primarily the optic nerves and spinal cord. Unlike multiple sclerosis (MS), NMOSD tends to result in more severe attacks that can lead to significant disability.

NMOSD was previously known as Devic's disease. It involves inflammation and demyelination, which leads to nerve damage and can result in visual impairment, weakness, or paralysis in the arms and legs, and issues with bladder and bowel function.