What is multiple sclerosis (MS)?

MS is a disease where patches of inflammation occur in parts of the brain and/or spinal cord. This can cause damage to parts of the brain and lead to various symptoms (described below).

Many thousands of nerve fibres transmit tiny electrical impulses (messages) between different parts of the brain and spinal cord. Each nerve fibre in the brain and spinal cord is surrounded by a protective sheath made from a substance called myelin. The myelin sheath acts like the insulation around an electrical wire, and is needed for the electrical impulses to travel correctly along the nerve fibre.

Nerves are made up from many nerve fibres. Nerves come out of the brain and spinal cord and take messages to and from muscles, the skin, body organs and tissues.

MS is thought to be an autoimmune disease. This means that cells of the immune system, which normally attack germs (bacteria, viruses, etc), attack part of the body. When the disease is active, parts of the immune system, mainly cells called T cells, attack the myelin sheath which surrounds the nerve fibres in the brain and spinal cord. This leads to small patches of inflammation.

Something may trigger the immune system to act in this way. One theory is that a virus, or another factor in the environment, triggers the immune system in some people with a certain genetic makeup.

The inflammation around the myelin sheath stops the affected nerve fibres from working properly, and symptoms develop. When the inflammation clears, the myelin sheath may heal and repair, and nerve fibres start to work again. However, the inflammation, or repeated bouts of inflammation, can leave a small scar (sclerosis) which can permanently damage nerve fibres. In a typical person with MS, many (multiple) small areas of scarring develop in the brain and spinal cord. These scars may also be called plaques.

Once the disease is triggered, it tends to follow one of the following four patterns.

Nearly 9 in 10 people with MS have the common relapsing-remitting form of the disease. A relapse is when an attack (episode) of symptoms occurs. During a relapse, symptoms develop (described below) and may last for days, but usually last for 2-6 weeks. They sometimes last for several months. Symptoms then ease or go away (remit). You are said to be in remission when symptoms have eased or gone away. Further relapses then occur from time to time.

The type and number of symptoms that occur during a relapse vary from person to person, depending on where myelin damage occurs. The frequency of relapses also varies. One or two relapses every two years is fairly typical. However, relapses can occur more or less often than this. When a relapse occurs, previous symptoms may return, or new ones may appear.

Excerpt from:
Multiple Sclerosis. Medical information about MS | Patient