Multiple sclerosis (MS) is characterized by damage to the myelin sheath which surrounds the nerves of central nervous system (brain, optic tract, and spinal cord). This damage is caused by inflammation and injury to the myelin sheaths as well as the underlying axons (nerve fibers).
Damaged areas undergo gliosis (scarring) and appear as lesions or scars scattered throughout the central nervous system. These scars may be found in areas around the ventricles in the brain; around the optic nerves; in the white matter in the optic nerves that control vision; and in the white matter of the spinal cord, brainstem, cerebellum, and cerebral area of the brain.
Over the past several years, researchers have found evidence of damage in the gray matter of the brain as well. The destruction of myelin interferes with nerve conduction, thus the symptoms of MS relate to this interruption of signaling between neurons (nerves of the central nervous system).
Damage to the underlying axons is likely to cause irreversible disability and was originally believed to occur late in the disease. However, recent research has shown that axonal damage can and does occur early as well as late in the disease.
Although it is unclear what exactly causes the abovementioned damage that leads to MS, various studies have shown evidence that points to a number of factors.
Researchers believe that a genetic predisposition may exist in the disease. There is no one gene that causes MS; it is believed that several genes play a role in predisposing a person to the disease. It is one of several risk factors for MS.
Immune System Attack
In addition, it is thought that the myelin loss associated with MS results from an attack by a person's immune system caused by sensitization to myelin (similar to an allergic response).
There is also research studying whether an infectious agent such as a bacteria or virus triggers this process which results in tissue destruction. This reaction against myelin or other healthy tissue causes a cascade of immunological events which is quite complicated. White blood cells called lymphocytes become activated and enter the central nervous system where they cause damage to the nervous tissue. There is a complex chain of events that occurs resulting in inflammation and ongoing damage.