Typically, the symptoms caused by these lesions are weakness, incoordination, paresthesias, speech disturbances, and visual disturbances, particularly diplopia. More specific signs and symptoms depend on the location of the lesions and the severity and destructiveness of the inflammatory and sclerotic processes. The course of MS is usually prolonged, with remissions and relapses over many years. Brief exacerbations, even with acute and severe symptoms, are thought to be the result of a transient inflammatory depression of neural transmission.
Recovery occurs when there has been no permanent damage to the myelin sheath during the attack.
Repeated attacks can, however, eventually permanently denude the axons and leave the yellow sclerotic plaques that are characteristic of the disease. Once the disease process reaches the stage of sclerosis the affected axons cannot recover and there is permanent damage. The prevalence of MS is not certain because the disease is not one that is reported, and mild cases can be either misdiagnosed or never brought to the attention of a physician. It is far more common in the temperate zones of the world than in tropical and subtropical climates. The onset of symptoms most often occurs between the ages of 20 and 40 years, and the disease affects both sexes about equally.