Neuromyelitis optica (NMO), also known as Devic’s disease, is an autoimmune disorder in which immune system cells and antibodies mistakenly attack and destroy myelin cells in the optic nerves and the spinal cord. The damage to the optic nerves produces swelling and inflammation that cause pain and loss of vision; the damage to the spinal cord causes weakness or paralysis in the legs or arms, loss of sensation, and problems with bladder and bowel function.
NMO occurs in two different forms: a single attack extending over a month or two, or a more common relapsing form in which the person experiences multiple attacks.
The cause of NMO is unknown.
Who gets NMO, and when?
There are an estimated 4,000 people with NMO in the United States and a half million people worldwide.
NMO is more common in women (greater than 60 percent) than men; more than 80 percent with the relapsing form are women.
The single episode form of NMO affects women and men equally.
NMO occurs in all parts of the world. NMO — rather than multiple sclerosis (MS) — may be the most common form of demyelinating disease in certain populations such as Africans, Asians and Native Americans.
NMO can occur at any age — in children as young as 3 and adults as old as 90 — but appears most often during childhood or between ages 40 and 50.
How is NMO different from MS?
NMO is considered to be an autoimmune disease (where the immune system reacts against healthy tissue as if it was a threat). In NMO, the immune system recognizes the aquaporin 4 molecule as foreign (aquaporin 4 antigen) and develops antibodies (NMO-IgG) to attack these cells. It is currently not known exactly how NMO-IgG results in damage to myelin.
No specific antigen has yet been identified in MS, leading many experts to conclude that MS cannot be classified as an autoimmune disease at this time.
Symptoms are generally more severe after an NMO attack in NMO than an MS attack.
NMO rarely has a secondary progressive stage as in MS; disabilities arise from the acute attacks.
NMO is present across the world; MS has a higher incidence in temperate climates and Caucasians.
Fatigue in NMO is usually an indirect result of the disease (secondary fatigue); in MS, the fatigue is usually the direct result of the disease (primary fatigue).
NMO usually affects only the optic nerve and spinal cord at the beginning of the disease, although there may be lesions present in specific areas of the brain. MS typically affects the brain as well as the spinal cord and optic nerve.
NMO-IgG is not found in people with MS but is found in 70 percent of those with NMO.
In MS, individual episodes are usually mild; their cumulative effect over time may or may not cause progressive disability. In NMO, the opposite is true and therefore early diagnosis is critical; acute episodes are usually severe and — if untreated — can have devastating, irreversible effects on function.