What Is It?
What is neuromyelitis optica (NMO)?
- NMO 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.
What other terms are used to refer to neuromyelitis optica?
- Devic's disease
What causes NMO?
- The cause of NMO is not known.
How is the immune system thought to be involved in NMO?
- Certain Immune system cells produce a substance called NMO-IgG, which mistakenly attacks the myelin cells in the optic nerves and spinal cord. It is currently not known exactly how NMO IgG results in damage to myelin.
- Some people with NMO also have other autoimmune diseases
- Sjogren’s Syndrome
- Systemic Lupus Erythematosus (SLE)
- Leber’s Hereditary Optic Neuropathy (LHON)
Who gets NMO?
- 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%) than men, and more than 80% 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 may be the most common form of demyelinating disease in certain populations such as Africans, Asians, and Native Americans.
When does NMO appear?
- NMO can occur at any age -- in children as young as 3 and adults as old as 90.
- NMO appears most often during childhood or between ages 40-50.
How is NMO similar to/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. 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 white races.
- 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% of those with NMO.
- Early diagnosis of NMO is critical. 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; acute episodes are usually severe and, if untreated, can have devastating, irreversible effects on function.