Multiple Sclerosis
Definition
Chronic disease of young adults; characterized pathologically by multiple central nervous system white matter lesions.
Epidemiology
Age at onset: peaks at 20 to 30 years; rare before age 10 or after 60. M:F ratio 1:1.4 to 1:3.1.
Prevalence related to geographic latitude. High-prevalence regions (>30/100,000 population): northern Europe, northern United States, southern Canada, southern Australia, New Zealand.
Prevalence related to geographic latitude: increases with increasing distance from Equator, up to 65 degrees north or south. Relevant latitude is place of residence before age 15. Prevalence up to 30/100,000 population in northern Europe, northern United States, southern Canada, southern Australia, New Zealand.
Etiology and Pathogenesis
Cause unknown. Postulated combination of genetic susceptibility and environment: initial trigger early in life (probably viral infection) leads to autoimmune mechanisms causing demyelination.
Genetic Susceptibility
Whites most susceptible. Lifetime risk of developing MS: 0.00125% in general population; 2.6% in siblings of MS patients; 1.8% in parents; 1.5% in children. Concordance rate 25% in monozygotic twins, 2.4% for same-sex dizygotic twins. Multiple genes suspected.
Immunology
Peripheral blood: no specific changes. CSF: pleocytosis, oligoclonal immunoglobulin G bands common. Histopathology: perivascular lymphocyte and macrophage infiltration.
Autoimmunity supported by animal model, experimental allergic encephalomyelitis.
Viruses
Environmental exposure implied by epidemiology. Epstein-Barr virus, Herpes simplex type 6 virus suggested as candidates.
Pathology
Macroscopic: diffuse brain atrophy common in long-standing cases. Brain sections: numerous small irregular gray areas in older lesions; pink areas in acute lesions (plaques), particularly in white matter tracts. Also periventricular.
Microscopic: myelin sheath stains show areas of demyelination in plaques. Sharply circumscribed, diffusely scattered throughout brain and spinal cord. Size varies. Acute lesion: marked hypercellularity, macrophage infiltration, astrocytosis, perivenous lymphocytes, plasma cells. Myelin sheaths disintegrate. Inactive plaque: prominent demyelination, severe loss oligodendrocytes, extensive gliosis.
Symptoms and Signs
MS usually manifests as one of three major clinical syndromes: relapsing-remitting, secondary progressive, or primary progressive.
Manifestations in all MS Types
Symptoms and signs (Table 134.1 and 134.2): determined by location of plaque. Frequently involved structures include optic nerves, corticospinal tracts, brainstem, cerebellum, spinal cord (especially lateral and posterior columns), giving rise to characteristic syndromes.
Common clinical features: optic neuritis (characteristically producing pain on eye movement); internuclear ophthalmoplegia (lesion of medial longitudinal fasciculus); hemiparesis or monoparesis; urinary incontinence or retention.
Table 134.1 Common Symptoms and Signs in Chronic Multiple Sclerosis | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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