Chorea is characterized by brisk, jerky, purposeless and graceful movements of the distal parts of the extremities, and is usually associated with twitching of the face. A slower version of chorea is athetosis that is characterized by slow, worm-like writhing movements of the extremities, affecting chiefly the fingers and the wrists.
Choreoathetosis is associated with the degeneration of the indirect striatopallidal pathway via sub-thalamic nucleus. Since the overall effect of this pathway is inhibitory, damage to this pathway results in hyperkinesia. Athetosis is frequently seen in damage of putamen as a result of birth-injury while chorea is mostly due to damage to the caudate nucleus.
Chorea may be genetically inherited or acquired. Examples of chorea that are genetically inherited are Huntington’s chorea and Wilson’s disease. Huntington’s chorea is associated with degeneration of caudate nucleus (most affected), putamen (moderately affected) and globus pallidus (least affected). Wilson’s disease (earlier called hepatolenticular disease) is the widespread manifestation of copper toxicity that occurs due to impaired biliary excretion of dietary copper. The toxic effects are most pronounced in the liver and the brain.
In brain, the lesions are widespread. However, the changes are most marked in the putamen and to a lesser degree, in the globus pallidus and caudate nucleus. Wilson’s disease is characteristically associated with low plasma levels of ceruloplasmin. This is because the increase in copper in liver cells inhibits the binding of copper to apoceruloplasmin: the two must be in an optimum proportion for the hepatic synthesis of ceruloplasmin.
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Acquired chorea is mostly immunological in origin. One of these is the Sydenham’s chorea, which occurs following streptococcal infection. Antibodies to P-hemolytic streptococci cross react with neurons of the corpus striatum and damage them.