Multiple Sclerosis (MS) is a chronic disease of the central nervous system (CNS) for which there is no known cause or cure. The disease is characterized by the destruction of the myelin sheath surrounding the nerves resulting in the formation of plaques. These plaques disrupt the transmission of nerve impulses leading to the symptoms of the illness which include, but are not limited to, spasticity, loss of balance and co-ordination, blurred or double vision, numbness, speech distortions, bladder and bowel problems, fatigue and cognitive dysfunction (Robinson, 1988). Plaques can occur in a variety of different sites resulting in substantial variation in the type and nature of the symptoms across individuals.

The course of the illness is also highly variable and unpredictable (Robinson, 1988). A small percentage of patients have a relatively benign course, characterized by an abrupt onset, little disease activity and no permanent disability. The majority have either a relapsing-remitting or a relapsing-progressive course. Patients experience periods of partial or total remission where the illness is inactive, interspersed with symptom relapses. Finally, MS can have a chronic-progressive course, in which there is a progressive worsening of symptoms and disability. Patients may be initially diagnosed with one type of MS, but over time progress to another.

There is substantial variation in the worldwide distribution of MS, with prevalence rates greater than 100 cases per 100 000 of population identified in many areas of the United Kingdom, Europe and North America.