Multiple sclerosis (MS) is a chronic condition that affects the central nervous system. This system includes the brain and spinal cord. It contains the nerves that control everything your body does, such as thinking, feeling, seeing, smelling, tasting, and moving. MS affects about 1 in 1,000 people and usually appears between the ages of 20 and 40, although it may occur at any age.
Your nerves are covered by an intact protective layer known as the myelin sheath. This covering helps to speed electrical signals in the brain. With MS, researchers think that the myelin sheath somehow becomes inflamed and damaged in small patches. It is not known what chain of events starts this damage, but once the injury occurs, electrical signals in the brain are slowed down.
It is believed that MS is an autoimmune disease (a condition in which an individual's immune system starts reacting against his or her own tissues) and cannot be spread from person to person. For unknown reasons, the immune system sees the myelin sheath as foreign and attacks it.
There are four types of MS:
Relapsing-remitting MS is the most common form of MS, affecting 85% of people with the condition. This type of MS is associated with "flare-ups" where symptoms worsen for weeks or months, and with remissions where symptoms completely or partially improve.
Primary-progressive MS affects 10% of people with MS and is associated with slow, but mostly continuous, worsening of the disease from the time of onset.
Secondary-progressive MS is associated with an initial period of relapsing-remitting disease followed by steady worsening and minor remissions. Approximately 50% of people with relapsing-remitting MS will develop this form of MS within 10 years.
Progressive-relapsing MS is associated with a steady worsening of the disease along with occasional flare-ups. This type is relatively rare and seen in only 5% of MS cases.