Neuromyelitis optica (NMO), also known as Devic's disease, is an uncommon neurological condition. A neurological condition is caused by disease or damage to the brain, spinal cord or nerves.
It most commonly affects the optic nerves and the spinal cord which leads to:
- Optic neuritis (inflammation of the nerve that leads from the eye to the brain) – causes a reduction or loss of vision, and can affect both eyes at the same time. Other symptoms include eye pain, which is usually made worse by movement, and reduced colour vision where colours may appear ‘washed out’ or less vivid than usual.
- Transverse myelitis (inflammation of the spinal cord) – causes weakness in the arms and legs which can range from a mild 'heavy' feeling in one limb, to complete paralysis in all four limbs. It may cause someone to be more sensitive to touch, cold, and heat and have numbness, tingling or burning below the affected area of the spinal cord. There may also be tight and painful muscle contractions (known as tonic muscle spasms).
In rare cases, parts of the brain can be affected. If the brain stem (the lower part of the brain connected to the spinal cord) is affected, it can cause symptoms such as vomiting, hiccups, and swallowing or speech difficulties.
In cases where a person experiences only optic neuritis or myelitis it is known as NMO spectrum disorder.
Relapses in NMO
The symptoms of NMO can range from mild to severe. There may only be one attack of optic neuritis or transverse myelitis, with good recovery and no further relapses for a long time.
However, in severe cases there can be a number of attacks which lead to disability. Disability occurs because the body cannot always fully recover from damage caused by the attacks on the spinal cord and the optic nerve.
What causes NMO?
NMO is an autoimmune condition which means a person’s immune system (the body’s natural defence again infection) reacts abnormally and attacks tissues and organs in the body. In cases of NMO, the immune system attacks the myelin sheath.
The exact cause of NMO is not fully understood because little is known about it. However, research has shown that up to 70% of people with NMO have an antibody called aquaporin-4 (AQP4) present in their blood. An antibody is a protein produced by the body to destroy disease-carrying organisms and toxins.
Who is affected?
NMO is a rare condition. In Europe, it is estimated that for every 1 million people there are 5-20 people with NMO. The condition is thought to be more common in people of Asian and African descent.
The condition can affect anyone, but is more common in women than men (with a ratio of 4:1) and people around 40 years of age.
NMO can sometimes be confused with multiple sclerosis (another condition that affects the brain and spinal cord) which has similar symptoms. The treatment for both conditions is different so it is important that the correct diagnosis is made.
There is no cure for NMO, so the aim of treatment is to manage attacks and symptoms, and prevent relapses. Every person with NMO is affected differently and some may have much milder symptoms than others. However, early treatment is usually needed to prevent further episodes and permanent disability.
Medication is used to reduce inflammation, suppress the immune system and treat any pain. Rehabilitation techniques, such as physiotherapy can also help with any reduced mobility that the relapses cause.