III. DEMYELINATING DISEASES RELATED TO INFLAMMATORY PROCESSES

A. Multiple Sclerosis (MS) -- characterized by more than one episode of neurologic deficits separated in time, attributable to CNS white matter lesions that are separated in space. This is an autoimmune disease, initially involving destruction of myelin.

1. Age of onset: 20-50 years of age, usually; more common in women

2. Pathological changes:

a. Multiple, sharply delineated areas (plaques) of demyelination in white matter of the brain and spinal cord (not the peripheral nervous system); perivenous distribution

b. The earliest detectable event in the development of a new lesion is an increase in permeability of the blood-brain barrier associated with inflammation. Demyelination occurs early in the inflammatory phase.

c. Gliosis within plaques

d. Loss of oligodendroctyes within plaques

e. Axons usually remain intact in plaques

f. Both CD4+ and CD8+ lymphocytes are present in active lesions.
Several multiple sclerosis plaques are seen adjacent to the lateral ventricles in this coronal section. A good example is at the upper right of the ventricle on the right side of the screen.

Several grayish multiple sclerosis plaques are adjacent to the occipital horns of the lateral ventricles. Choroid plexus is seen within the ventricles.


3. CSF changes: Gamma globulin elevated in most patients (due to proliferation of B cells within the nervous system); oligoclonal bands are present after CSF electrophoresis

4. Clinical course - variable (in all forms, presenting symptoms vary widely, but visual impairment due to optic neuritis is a common initial symptom):
a. Remitting and relapsing course (about 60%)

b. Acute progressively downhill course

c. Slowly progressive course

d. Benign course

5.Epidemiology:
a. In general, the frequency increases at higher latitudes (toward both poles). Individuals take on the relative risk of the environment in which they spent their first 15 years.

b. There are significant genetic influences. Linkage studies have indicated associations with several MHC antigens.


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