Understanding NMOSD

Neuromyelitis optica spectrum disorder (NMOSD) is a rare neurological disease that often presents with unpredictable occurrences of vision loss and inability to move.1,2 This is caused by the body’s own defence mechanism, the immune systemThe body’s defence system that protects against disease and infection (e.g. bacteria and viruses), mistakenly attacking healthy cells and proteins in the body and causing inflammation, mainly in the eyes (optic neuritis) Inflammation of the optic nerve and spinal cordThe bundle of nerves that runs from the brain through the spine (acute myelitis)Inflammation of the spinal cord.1,3

The normal function of the immune system is to fight off infections when foreign microorganisms, such as bacteria and viruses, enter the body.4 In NMOSD, the immune system is activated by mistake to attack the body’s own cells, which is why NMOSD is characterised as an autoimmune diseaseA condition in which the body’s immune system mistakenly attacks and damages healthy cells and tissues.1,4

NMOSD affects about 1–10 people per 100,000 worldwide, though these estimates may vary among different studies.1,2

NMOSD is more likely to first appear in individuals between the ages of 30–40 years,1,2 though it can affect people at any age from childhood to late adulthood.1
In most individuals with NMOSD, the body’s immune systemThe body’s defence system that protects against disease and infection (e.g. bacteria and viruses) produces specific proteins, known as autoantibodiesAntibodies produced by the immune system that mistakenly target and attack the body’s own tissues or cells .1,6,7 The produced autoantibodies mistakenly target another protein in the body called a aquaporin-4 (AQP4)A protein that acts as channels for water and is most abundant in the brain, spinal cord and the optic nerve, which is crucial for the water transport in various cells of the body.1,6,7 This leads to activation of the complement systemProteins in the blood that help to fight infection and are part of the immune system6,7 – a part of our immune system that normally helps fight disease by clearing up the foreign molecules and damaged cells.8,9 However, in NMOSD, complement activation causes in inflammation and damage to the body’s own cells within the central nervous system (CNS)The part of the nervous system comprised of the brain and spinal cord, in most cases those in the spinal cordThe bundle of nerves that runs from the brain through the spine (acute myelitisInflammation of the spinal cord) and eyes or optic nerveThe nerves that run from the back of the eye (retina) to the brain and transmit light information from the eye to the brain (optic neuritisInflammation of the optic nerve).3,6,7,10
Although the majority of people with NMOSD have no relatives with the disease, about 3% have a family history of the condition.10 People with existing autoimmune diseasesA condition in which the body’s immune system mistakenly attacks and damages healthy cells and tissues may be at higher risk for developing NMOSD.2 Environmental factors may also play a role in the development of NMOSD, though there is little clarity around the identification of such factors.1,2
AQP4, aquaporin-4; NMOSD, neuromyelitis optica spectrum disorder.
Wingerchuk DM, Lucchinetti CF. Neuromyelitis optica spectrum disorder. N Engl J Med. 2022;387(7):631–639. Holroyd KB, Manzano GS, Levy M. Update on neuromyelitis optica spectrum disorder. Curr Opin Ophthalmol. 2020;31(6):462–468. Neuromyelitis Optica. National Institute of Neurological Disorders and Stroke. Available at: https://www.ninds.nih.gov/health-information/disorders/neuromyelitis-optica. Last accessed: May 2023. Immune System and Disorders: MedlinePlus. National Library of Medicine. Available at: https://medlineplus.gov/immunesystemanddisorders.html. Last accessed: May 2023. Mutch K, et al. Life on hold: The experience of living with neuromyelitis optica. Disabil Rehabil. 2014;36(13):1100–1107. Chamberlain JL, et al. Role of complement and potential of complement inhibitors in myasthenia gravis and neuromyelitis optica spectrum disorders: A brief review. J Neurol. 2021;268(5):1643–1664. Dutra BG, et al. Neuromyelitis optica spectrum disorders: Spectrum of MR imaging findings and their differential diagnosis. Radiographics. 2018;38(1):169–193. Complement System. Cleveland Clinic. Available at: https://my.clevelandclinic.org/health/body/23370-complement-system. Last accessed: May 2023. Merle NS, et al. Complement system Part 2: Role in immunity. Front Immunol. 2015;6:257. Weinshenker BG, Wingerchuk DM. Neuromyelitis spectrum disorders. Mayo Clin Proc. 2017;92(4):663–679.