Due to the part of the nerve affected by the condition, NMO is classified as a demyelinating disease. The protective covering of a nerve is formed from a substance called myelin. Demyelinating diseases target this covering.
The condition is extremely rare, affecting between 0.052 and 0.44 in every 100,000 people worldwide.
The disease is more common in people over 40 years of age.
This MNT Knowledge Center article will explain the types, causes, symptoms, and treatments for NMO, as well as explaining how the condition is diagnosed and ways it can complicate.
- The two types of Devic's disease, or neuromyelitis optica (NMO) are relapsing NMO and monophasic NMO, and the type depends on the frequency of attacks.
- Symptoms can include a temporary loss of eyesight, eye pain, and altered sensations in the limbs.
- The cause is unknown, and there is no cure.
- Treatment aims to prevent relapses and control symptoms.
NMO damages the protective covering of the optic nerve and nerves in the spinal cord.
There are two types of NMO: Relapsing, which is the most common, and monophasic, which is rare.
With this type, there is an initial attack of inflammation in the optic nerve and spinal cord followed by attacks over a period of several years. Further research is required to confirm what triggers these attacks.
The individual may not be able to fully recover from the nerve damage caused by these attacks cause, and the damage is often permanent. This can cause disability and affects females more frequently than males.
A limited number of attacks is experienced over a period of days or weeks. There are no subsequent attacks. This form of NMO affects both sexes equally.
It is easier for an individual to recover from monophasic NMO.
The type of NMO will affect how severe symptoms are as well as the likelihood of complications and disability. Relapsing NMO is by far the most common, with 90 percent of people experiencing more than one attack.
Signs and symptoms of NMO vary. A person with NMO will experience at least one bout of inflammation of the optic nerve and spinal cord.
Symptoms of optic nerve inflammation, termed optic neuritis (ON), include:
- temporary loss of eyesight affecting at least one eye, with a risk of permanent vision loss
- swelling of the optic disc
- pain in the eye that generally gets worse with movement, and tends to become more severe after a week then resolve in a few days
- reduced sensitivity to color
People who develop optic neuritis should not drive a vehicle due to reduced vision. They may also develop symptoms in the spinal cord from a process called transverse myelitis (TM) including:
- altered sensations, with sensitivity to temperature, numbness, tingling, and a sensation of coldness or burning
- weak, heavy limbs, sometimes leading to total paralysis
- changes in urination patterns, including urinary incontinence, difficulty urinating, and more frequent urination
- fecal incontinence or constipation
A person with NMO may have just one mild attack of ON and one episode of TM, recover completely, or almost completely, and have no more relapses ever. Others may have several attacks throughout their life and experience lifelong disability.
NMO spectrum disorder is a term used for individuals who experience inflammation of either the optic nerve or spinal cord but not both.
In most cases, just the optic nerve and spinal cord are affected. In very rare cases, parts of the brain may also be affected. When the brain stem is affected, an individual may experience uncontrollable hiccups or vomiting.
The exact causes of NMO have not yet been confirmed. NMO is an autoimmune disorder, meaning that the immune system mistakenly attacks healthy cells in the optic nerve and spinal cord.
The condition does not run in families. In some rare cases, tuberculosis (TB) and some environmental organisms have been linked to the development of NMO. However, scientists have not been able to isolate specific organisms so far.
Many people with NMO have an antibody called Neuromyelitis Optica Immunoglobin G (NMO IgG) in the blood. Research suggests that NMO IgG may damage aquaporin-4, the water channel that surrounds optic nerve and spinal cord cells, causing the inflammatory effect of the condition.
However, more research is required to confirm the exact triggers of both the condition and its attacks.
NMO can be difficult to diagnose, as it presents signs and symptoms which are often similar to those found in other diseases, such as:
- multiple sclerosis (MS)
- acute demyelinating encephalomyelitis (ADEM)
- systemic lupus erythematosus (SLE)
- mixed connective tissue disorder (MCTD)
- some viral inflammations
- an inflammation linked to cancer called paraneoplastic optic neuropathy
The following tests can help rule out other conditions.
- Blood tests: These test for the antibody NMO IgG.
- Lumbar puncture test, or spinal tap: These collect a small amount of fluid from the brain and spinal cord. Results will indicate high levels of white blood cells and the presence of specific proteins linked to NMO or other conditions.
- MRI scan: This scan can show damage and lesions on or around the nerves. MRI scans of people with NMO show changes associated with optic neuritis, and will show up lesions consisting of three or more segments of the spinal cord. This type of spinal cord lesion makes it easier for the doctor to rule out MS.
Physical therapy can help to increase mobility and ease discomfort.
There is no cure for NMO. However, there are treatments that can help some of the symptoms as well as the frequency and intensity of relapses.
Steroids: A doctor may prescribe steroids, such as injected methylprednisone. The patient would take a course of oral steroids following the injection.
Plasma exchange therapy, or plasmapheresis: This treatment is usually given to people with NMO who have not responded to steroid treatment. Plasma exchange removes from the blood the antibodies that cause inflammation. The blood is removed, and the blood cells are separated from plasma. The blood cells, diluted with fresh plasma or a substitute, are returned to the bloodstream.
Preventing relapses: If the patient's immune system can be suppressed, the chances of relapses are significantly reduced. Azathioprine (AZT), a medication that suppresses immune activity, is sometimes prescribed. The doctor may prescribe a combination of AZT and steroids.
AZT can cause the following side effects:
The anticonvulsant drug carbamazepine may be prescribed for pain, urinary problems, muscle spasms, and stiffness. Carbamazepine is often used with people who have other demyelinating diseases.
Physical therapy, rehabilitation, mobility, and visual aids may also be provided to help return function and ease discomfort if the damage is permanent and the person with NMO experiences ongoing disabilities.
NMO can lead to a range of effects in various systems, including:
- Breathing problems: This occurs as a result of muscle weakness. For people with severe NMO, muscles may become so weak that they need artificial ventilation.
- Depression: The mental strain of living with NMO, especially if symptoms are severe, can lead to clinical depression.
- Erectile and sexual dysfunction: Some men may experience problems achieving or maintaining an erection. Both men and women may experience difficulties achieving an orgasm.
- Fragile bones: Long-term steroid therapy can lead to osteoporosis. Tiny pores occur in the bones, making them weak and prone to fracture.
- Paralysis: People with NMO that severely damages the spinal cord can cause limb paralysis.
- Vision loss: Permanent loss of vision can occur, due to severe damage to the optic nerve.
The likelihood of complications and the outlook of a person with the condition depend on the severity of the initial attack and the number of relapses. The age a person is when they first experience the condition also contributes.
Relapsing NMO normally leads to permanent vision loss, paralysis, or muscle weakness within 5 years. Respiratory failure as a result of the condition can be fatal in 25 to 50 percent of people with NMO.