Multiple Sclerosis

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Overview, Causes, & Risk Factors

The cause of MS is unknown. The disease involves repeated episodes of inflammation of nervous tissue in any area of the central nervous system (brain and spinal cord). These episodes occur when the body's own immune cells attack the nervous system. The location of the inflamed areas varies from person to person and from episode to episode. The inflammation destroys the covering of the nerve cells in that area (myelin sheath), leaving multiple areas of scar tissue (sclerosis) along the covering of the nerve cells. This results in slowing or blocking the transmission of nerve impulses in that area, leading to the symptoms of MS.

Symptoms vary because the location and extent of each attack varies. There is usually a stepwise progression of the disorder, with episodes that last days, weeks, or months alternating with times of reduced or no symptoms (remission). Recurrence (relapse) is common although non-stop progression without periods of remission may also occur.

The exact cause of the inflammation associated with MS is unknown. Geographic studies indicate there may be an environmental factor involved. MS is more likely to occur in northern Europe, the northern United States, southern Australia, and New Zealand than in other area. The "intertropical belt" seems to have much lower rates of this condition. There seems to be a genetic link to the disease, with some families more likely to be affected than others and certain genetic markers are more common in people with MS than in the general population.

An increase in the number of immune cells in the body of a person with MS indicates that there may be a type of immune response that triggers the disorder. The most frequent theories about the cause of multiple sclerosis include a virus-type organism, an abnormality of the genes responsible for control of the immune system, or a combination of both factors.

Multiple sclerosis (MS) affects approximately 1 out of 1,000 people. Women are affected more commonly than men. The disorder most commonly begins between 20 to 40 years old, but can happen at any age. Risks include a family history of MS and living in a geographical area with a higher incidence rate for MS.