Neuromyelitis Optica Overview:
Neuromyelitis Optica (NMO) is an autoimmune disease of the central nervous system (CNS) that predominantly affects the optic nerves and spinal cord. It is sometimes also referred to as NMO spectrum disorder. In NMO, the body’s immune system mistakenly attacks healthy cells and proteins in the body, must often those in the spinal cord and eyes. Individuals with NMO develop optic neuritis, which caused pain in the eye and vision loss.
While for some time NMO was considered by some researchers and clinicians to be a form of multiple sclerosis in is in fact a seperate disease.
Individuals also develop transverse myelitis, which causes weakness or paralysis of arms and legs,and numbness, along with loss of bladder and bowel control Magnetic resonance imaging of the spine often shows an abnormality that extends over long segments of the spinal cord.
Individuals may also develop episodes of severe nausea and vomiting, with hiccups from involvement of a part of the brain that controls vomiting The disease is caused by abnormal autoantibodies that bind to a protein called aquaporin-4. Binding of the aquaporin-4 antibody activates other components of the immune system, causing inflammation and damage to these cells. This also results in the brain and spinal cord the loss of myelin, the fatty substance that acts as insulation around nerve fibers and helps nerve signals move from cell to cell.
NMO is different from multiple sclerosis (MS). Attacks are usually more severe in NMO than in MS, and NMO is treated differently than MS. Most individuals with NMO experience clusters of attacks days to months or years apart, followed by partial recovery during periods of remission. Women are more often affected by NMO than men. African Americans are at greater risk of the disease than are Caucasians. The onset of NMO varies from childhood to adulthood, with two peaks, one in childhood and the other in adults in their 40s.
Neuromyelitis optica (NMO) and NMO Spectrum Disorder (NMOSD), also known as Devic’s disease, primarily attack 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 is a relapsing-remitting disease, like MS. During a relapse, new damage to the optic nerves and/or spinal cord can lead to accumulating disability. Unlike MS, there is no progressive phase of this disease. Therefore, preventing attacks is critical to a good long-term outcome.
The cause of NMO is thought to be due to a specific attack on the aquaporin-4 (AQP4) water channel located within the optic nerves and spinal cord. Aquaporins (AQPs) are proteins that transport water across cell membranes. More than 70% of NMO and NMOSD patients test positive for an antibody biomarker in the blood called the NMO-IgG or anti-AQP4 antibody.
Who gets Neuromyelitis Optica, and when?
There are an estimated 4,000 people with NMO in the United States and a quarter-million people worldwide.
- NMO is more common in women (greater than 80 percent) than men.
- NMO occurs in all parts of the world and 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 between ages 40 and 50.
How is Neuromyelitis Optica 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 AQP4 water channel as foreign and develops antibodies (NMO-IgG or anti-AQP4 antibody) to attack AQP4 on the surface of astrocytes, which in turn damages the astrocytes. Astrocytes are supportive cells in the brain, spinal cord and optic nerves, and damage to astrocytes is believed to lead to demyelination. AQP4 belongs to the aquaporin family of integral membrane proteins that conduct water through the cell membranes.
NMO is an autoimmune disease, with MS no specific immune target 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 than an MS attack.
- NMO rarely has a secondary progressive stage as in MS; disabilities accumulate from repeated acute attacks.
- NMO is present across the world, especially among non-Caucasians; 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 (anti-AQP4 antibody) 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 not 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.
- Some people with NMO also have other autoimmune diseases such as Sjogren’s Syndrome or Systemic Lupus Erythematosus (SLE).
Treatment of Neuromyelitis Optica:
There is no cure for NMO and no FDA-approved therapies, but there are therapies to treat an attack while it is happening, to reduce symptoms, and to prevent relapses.NMO relapses and attacks are often treated with corticosteroid drugs and plasma exchange (also called plasmapheresis, a process used to remove harmful antibodies from the bloodstream). Immunosuppressive drugs used to prevent attacks include mycophenolate mofetil, rituximab, and azathioprine. Pain, stiffness, muscle spasms, and bladder and bowel control problems can be managed with medications and therapies. Individuals with major disability will require the combined efforts to physical and occupational therapists, along with social services professionals to address complex rehabilitation needs.
Prognosis of Neuromyelitis Optica:
Most individuals with NMO have an unpredictable, relapsing course of disease with attacks occurring months or years apart. Disability is cumulative, the result of each attack damaging new areas of the central nervous system. Some individuals are severely affected by NMO and can lose vision in both eyes and the use of their arms and legs. Most individuals experience some degree of permanent limb weakness or vision loss from NMO. However, reducing the number of attacks with immunosuppressive medications may help prevent with accumulation of disability. Rarely, muscle weakness can be severe enough to cause breathing difficulties and may require the use of artificial ventilation.
Neuromyelitis Optica Research:
The mission of the National Institute of Neurological Disorders and Stroke (NINDS) is to seek fundamental knowledge of the brain and nervous system and to use that knowledge to reduce the burden of neurological disease. The NINDS is a component of the US National Institutes of Health, the leading supporter of biomedical research in the world. NINDS researchers are working to better understand the process by which the immune system destroys or attacks the nerve insulating substance called myelin in autoimmune diseases or disorders. Other work focuses on strategies to repair demyelinated spinal cords, including approaches using cell transplantation. this research may lead to a grater understanding of the mechanisms responsible for damaging myelin and may ultimately provide a means to prevent and treat transverse myelitis An NINDS-funded study comparing clinical MRI and lumbar puncture of healthy individuals to those with symptoms of immune-related central nervous system damage hopes to identify processes or mechanisms to inhibit or minimize spinal tissue damage and enhance recovery mechanisms. Multiple studies are looking at ways to target different components of the immune system known to be involved in NMO spectrum disorders to allow more directly targeted treatment of this disease.
