What is NMOSD?

* Revised 7/13/2021. This information sheet has been reviewed and approved by members of SRNA’s Medical and Scientific Council.

Neuromyelitis Optica Spectrum Disorder (NMOSD) is a rare relapsing autoimmune disorder that preferentially causes inflammation in the optic nerve and spinal cord. It is sometimes referred to as Devic’s Disease, as it was first described by Eugène Devic in 1894, and he coined the term “neuro-myélite diffuse aigüe.” It is typically characterized by longitudinally extensive transverse myelitis (LETM, myelitis which is 3 vertebral segments in length or greater), which can leave one quite debilitated at presentation, and unilateral or bilateral optic neuritis. Individuals can present with short lesions as well. It was once thought of as a variant of Multiple Sclerosis (MS) and is still oftentimes misdiagnosed as MS. However, several factors can differentiate it from MS: 1) it typically involves different parts of the brain than in MS, 2) the severity of attacks can be more robust as compared to MS, and 3) the pathophysiology differs from MS – whereas MS does not have a known antibody, NMOSD is associated with the antibodies against the aquaporin-4 water channel. Blood testing for the aquaporin-4 antibody (NMO-IgG) test is highly specific (>99%) and its sensitivity ranges from 48-87%, depending on the assay used. Antibodies to Myelin Oligodendrocyte Glycoprotein or anti-MOG have been found in individuals diagnosed with NMOSD who are negative for the aquaporin-4 antibody. Those with MOG antibody disease tend to have attacks most often in the optic nerve, or optic neuritis (ON). Regardless of antibody status, treatment for acute relapses includes IV methylprednisolone and/or plasma exchange (PLEX), and prevention of future attacks with immunosuppressants and aggressive rehabilitation. In addition to off-label use of immunosuppressants, including rituximab and mycophenolate, three immunotherapies have been recently FDA approved for preventive treatment of aquaporin-4 antibody positive patients: eculizumab, inebulizumab, and satralizumab.

Previously, the disorder was split into two categories: Neuromyelitis Optica and Neuromyelitis Optica Spectrum Disorder, whereby the former definition required both optic neuritis and transverse myelitis to make the diagnosis and the latter allowed for only one attack in the context of a positive aquaporin-4 antibody test. The International Panel for NMO Diagnosis (IPND) released an updated set of guidelines in 2015 in which the term NMOSD includes all aquaporin-4 seropositive patients with even a single inflammatory attack, plus seronegative patients with both optic neuritis and transverse myelitis.