What is neuromyelitis optica? | Who is affected? | What are symptoms of NMO?| Diagnosis of NMO? | What are the causes of NMOs?
Neuromyelitis optica (NMO) is a rare demylenating disease of the nervous system, which affects mainly the spinal cord and the optic nerves. NMO is also know as Devic’s Disease named after Eugene Devic who first summarized the symptoms in 1894.
There are two main types of neuromyelitis optica:
1)Relapsing neuromyelitis optica:
There is an initial attack of optic neuritis and transverse myelitis, and then subsequent attacks over a period of several years. Sometimes the patient cannot recover fully from the neurological damage the attacks cause to the optic nerve and/or spinal cause and the damage is permanent, causing disability. This type of neuromyelitis optica affects females more frequently than males.
2)Monophasic neuromyelitis optica:
Few attacks are experienced over a period of days or weeks. There are no subsequent attacks. This form of neuromyelitis optica affects both sexes equally.
The onset of NMO varies from childhood to adulthood, with two peaks, one in childhood and the other in adults in their 40s.Females are affected more than males ratio with a ratio greater than 4:1
The most common symptoms are:
1. Optic neuritis is an inflammation, with accompanying demyelination, of the Optic Nerve serving the retina of the eye. Typically one eye is affect at a time but both eyes can be affected. Optic neuritis is also associated with eye movement pain.
2. Transverse Myelitis is inflammation of the spinal cord, which causes weakness, numbness or other sensory disturbances. It can also cause disturbances of bladder and bowel function. The degree of weakness or numbness depends on the location and severity of the inflammation of the spinal cord.
Diagnosis of Optica neuritis using:
- complete medical examination, including chemical analysis of the blood can help rule out related diseases.
- An Ishihara color chart and/or Farnsworth-Munsell hue tests are often used to evaluate the degree of dyschromatopsia (reduced color vision). down the optic nerve, are also used as a diagnostic test for optic neuritis.
- Visual evoked potential tests, which detect the speed of nerve transmissions
Diagnosis of Transverse Myelitis using:
- An MRI consisting of three spinal segments or longer while the attack is taking place.
Lumbar puncture test (spinal tap)
- a small amount of fluid surrounding the brain and spinal cord is collected. Results will indicate whether levels of white blood cells are high, and also whether specific proteins linked to NMO or other conditions are present.
The presence of NMO IgG
- This can help to confirm diagnosis of NMO, but is not mandatory for diagnosis. An abnormal MRI of the brain does not exclude NMO. It’s important to understand that criteria are generalizations and for guidance only. Each case has to be assessed separately.
NMO is an autoimmune disorder and in the case of NMO, the person’s immune system starts attacking good,healthy tissue, such as there optic nerve and their spinal cord. Medical experts are not sure why autoimmune diseases, such as NMO occur. The immune system of a patient with NMO attacks the myelin sheath, the protective blanket for the spinal cord and optic nerve.
Scientists have revealed that over two-thirds of patients with NMO have an antibody called NMO IgG (Neuromyelitis Optica Immunoglobin G) in their blood. Scientists hypothesize that most likely NMO IgG damages Aquaporin 4, the water channel that surrounds optic nerve and spinal cord cells, resulting in NMO.
There is no known cure for NMO, but there are therapies to treat an attack, to reduce symptoms, and to prevent relapses. The initial NMO attack is treated with a combination of a corticosteroid drugs to stop the attack, and an immunosuppressive drug to prevent any additional attacks. Some individuals may need
to continue a low dose of steroids for longer periods if they have many relapses. Plasma exchange is a technique that separates antibodies out of the blood stream and is used with people who are unresponsive to corticosteroid therapy. Other symptoms, such as; neuropathy, pain, stiffness, muscle spasms, bladder and bowel control problems can be treated with medications and therapies.
Most individuals with NMO face lapses occurring months or years apart without the foreseeable prediction of their onset. The occurrences of relapses that repeatedly damage the myelin in different areas leave behind a disabling effect that is cumulative. The majority of individuals with NMO experience a moderate degree of permanent limb weakness from myelitis with some individuals so severely affected they can lose vision in both eyes as well as the use of their arms and legs. The death of an individual with NMO is most often caused by respiratory complications from myelitis attacks as muscle weakness can make breathing difficult.