Etiology

Despite a great interest in the disease and ample experimental and pathologic studies, the etiology remains elusive. A combination of genetic susceptibility and

FIGURE 8.10

MRI of acute MS plaques in a 48-year-old man with relapsing MS. Gadolinium-enhanced T1-weighted axial image shows one ring-like enhancing and few homogenously enhancing lesions.

environmental factors are implicated in the etiology. Familial occurrences are recognized, and the disease has been reported in monozygotic and dizygotic twins. Certain major histocompatibility complexes (MHC)— HLA-DR2, HLA-A3, HLA-B7—are more frequent among MS patients than among the general population.

Individuals with HLA-DR2 on chromosome 6 are particularly susceptible to developing MS.

Epidemiologic data indicate a higher incidence of MS in certain geographic areas and among particular ethnic groups. The incidence is higher in northern Europe, the northern United States, and Canada. It is also higher in people of Anglo-Saxon and Scandinavian descent, and lower among Japanese and Chinese. In the United States, the incidence is lower among African American than it is among whites.

Exposure to an as yet unidentified infectious agent probably occurs during the early years of life. As mentioned, the incidence of the disease is higher in cold and temperate climates. Studies indicate that persons who migrate from a cold climates to a warm climate after 15 years of age keep the higher risk of their native locality. Conversely, persons who migrate before age 15 years acquire the lower risk of their new locality.

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