Multiple Sclerosis
It is a disease of the myelin, the white covering of the nerve cell axons. Myelin is composed of specialized glial support cells. In the central nervous system, these are the oligodendrocytes. In the peripheral nervous system myelin is composed of Schwann cells. Consequently, the disease is most apparent in the white matter pathways of the brain. There are usually multiple areas of degenerated myelin and inflammation called plaques. These result in neuronal dysfunction and impairment. The initial neurological symptoms may reflect the patient's greatest functional impairment rather than all the areas containing plaques. The cause of this inflammation and degeneration of the myelin is unknown. One commonly accepted theory is that the inflammation episodes and plaques represent a response of the patient's immune system. Loss of myelin reduces the efficiency of nerve conduction. The most common symptoms are slight or incomplete paralysis (paresis), abnormal sensations (paresthesias), and visual impairment. The onset and progression of symptoms vary considerably from case to case. The great majority of cases will have exacerbations and remissions of symptoms.