An Overview of Multiple Sclerosis

Joseph B. Guarnaccia, MD and John Booss, MD

Multiple sclerosis (MS) is a disease of myelin, the insulating cover around the nerves of the central nervous system (CNS: brain, optic nerves, and spinal cord) (see Figure 1.1), that becomes damaged in MS. MS most commonly begins in young adulthood and affects about twice as many women as men. Although its initial symptoms vary greatly, certain patterns are typical: a previously healthy woman or less frequently, a man, 20 to 30 years old suddenly experiences neurologic symptoms. These symptoms may range from dimming of vision to numbness in the legs or body to dizziness or imbalance. Symptoms of this first attack (or exacerbation) usually remit (clear) or improve.

Four general patterns of disease course are diagnosed as MS (see Figure 1.2). Relapsing-remitting MS is a pattern of attacks (exacerbations) followed by partial or complete recovery from symptoms (remission). This relapsing/remitting pattern may give way to a pattern of progressive disability, called secondary progressive MS.

Some individuals rarely experience remission of symptoms. They have primary progressive MS, in which there is steady progression without remissions. A fourth pattern, recently defined, is progressive-relapsing MS. This is a chronic progressive course in which infrequent relapses occur.

The reasons for these differences in the course of MS are unknown. However, the relapsing-remitting pattern most typically affects young adults, especially women. Older individuals are more likely to have patterns of progressive MS. In these latter cases, onset is usually after age 40, and men and women are affected equally.

The multiple scars of MS (plaques) can be seen as pale, well-defined patches scat-

Figure 1.2

Disease Course Classifications in MS

Figure 1.2

Disease Course Classifications in MS

Relapsing-remitting

Relapsing-remitting

Time

Pri mary-prog ressi ve

Pri mary-prog ressi ve

Time

Time

Secondary-progressive

Secondary-progressive

Time

Progressive-relapsing

Progressive-relapsing

Time

Time tered throughout the brain and spinal cord. They are located in the white matter, which contains a high percentage of myelin, an insulating material that covers sections of nerve cells that carry electrochemical messages from the nerve cells to "action" parts of the body, such as the eyes or the muscles in the hands or legs. Because many of these messages from the brain must travel relatively long distances, myelin is critical for impulse conduction (see Figure 1.3). In MS, myelin is the primary target of an attack by the body's immune system, although damage to the underlying nerve is now known to occur. Multiple sclerosis is an autoimmune (self-immune) disease, because the body's immune system mistakenly attacks healthy myelin.

Figure 1.3

Myelinated Axon

- Dendrites

Figure 1.3

Myelinated Axon

- Dendrites

Myelin sheath

Neuron

Myelin sheath

Neuron

— Axon common in northern states than in southern states. Possible reasons for these variations are discussed in the next section.

However, whatever factors in high-risk zones predispose the development of MS, exposure to them during childhood or adolescence seems to have the greatest effect. If an individual moves after that critical period from a high-risk zone to a lower risk zone, or vice versa, the risk level of the original habitat applies. For example, a person who moves after adolescence from a temperate, high-risk zone to a tropical, low-risk zone will continue to have a higher risk of developing MS than the population in the tropical zone. What makes this observation intriguing is that MS does not usually begin in individuals until they reach their twenties and thirties—years or even decades after the period when MS is thought to originate.

Location alone does not account for all the variability, however. Multiple sclerosis is also more common in people of certain ethnic or racial backgrounds. Parts of the British Isles have the highest concentration of MS in the world, affecting one out of every hundred. Immigrants of Northern European descent have colonized other high-incidence areas of the world, including the United States and Canada. By contrast, MS is rare to nonexistent among African natives, Native Americans, and Laplanders in Scandinavia.

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