Introduction

Multiple sclerosis (MS) is a disease of the central nervous system (CNS), the nerves that comprise the brain and spinal cord. It has two major features:

• Destruction of myelin, a fatty insulation covering the nerve fibers, is the main characteristic of MS. The end results of this process, called demyelination, are multiple patches of hard, scarred tissue called plaques. (Multiple sclerosis is well named. Sclerosis comes from the Greek word skleros, which means hard.)
• Destruction of axons, the long filaments that carry electric impulses away from a nerve cell, is also a major factor in the permanent disability that occurs with MS.

The symptoms, severity, and course of MS vary widely depending partly on the sites of the plaques and the extent of the demyelination. Experts generally group multiple sclerosis into two major symptom categories:

• Relapsing-remitting
• Chronic-progressive

Chronic-progressive MS is often subcategorized as primary-progressive, secondary-progressive, and progressive-relapsing.

Recent evidence suggests that the disease process starts long before symptoms begin. By the time symptoms appear, there are often already signs of brain and spinal cord atrophy. The cause of MS is unknown, and it cannot be prevented or cured. It is not fatal, however, and great progress is being made in treating it and identifying underlying mechanisms that trigger this disease.

Relapsing-Remitting Multiple Sclerosis

Relapsing-remitting multiple sclerosis generally occurs in younger people and is the most common form of MS. It generally follows this course:

• Most patients first experience a single attack of symptoms called a clinical isolated syndrome, which typically occurs between the ages of 20 - 40 years. Once a second attack occurs, the patient is considered to have relapsing-remitting multiple sclerosis.
• The characteristic feature of relapsing-remitting MS is the attack (also referred to as relapse, flare-up, or exacerbation), which is a bout of specifically MS symptoms (facial pain, Lhermitte's sign, or bladder instability) that lasts at least 24 hours and typically several days. Such attacks are fairly mild in about half of patients with this form of MS.
• The disease then goes into remission (when symptoms improve or disappear), usually for about 4 - 8 weeks. To be considered in remission, attacks need to be separated by at least 30 days. Remission periods may be spontaneous or induced by immunosuppressive drugs. A person with multiple sclerosis in remission may have subtle attacks and not realize it. For example, hands may be a little numb for a few days, or there may be slight awkwardness in gait or coordination.
• Remissions are almost always followed by relapses, in which symptoms flare-up or the patient has a period of deteriorating ability.

About 20% of patients with relapsing-remitting MS experience little or no progression after a first attack for long periods of time, although by 25 years most patients have converted to a progressive phase.