The peripheral and central nervous tissues of eight patients dying of acute poliomyelitis were examined histologically to discover whether and to what extent the distribution of lesions was consistent with the hypothesis that virus enters the mucous membranes through the superficial nerve fibers, infects the neurons in peripheral ganglia, and proceeds thence into the central nervous system to infect connecting centers. Evidence consistent with this hypothesis was found in all cases. Based on concurrent lesions in the primary and secondary centers, the frequency of involvement of the various systems and the probability of their having acted as primary pathways for entering infection may be summarized as follows:—
(a) Trigeminal afferent system (V cranial): very frequent.
(b) Visceral afferent system (IX and X cranial): fairly common but less than V.
(c) Gustatory system (VII, IX, and X cranial): occasional.
(d) Sympathetic system, upper levels (pharynx, bronchial tree, upper esophagus): occasional.
(e) Sympathetic system, lower (intestine): occasional or doubtful.
(f) Vagal efferent (parasympathetic) system (X cranial) and olfactory (I cranial) system: uninvolved.
In general, the evidence of penetration through the upper alimentary and respiratory tracts was more conspicuous and consistent than through the lower alimentary tract. The pharynx appears to be an especially favorable site for the primary penetration of virus into the body.
Our data suggest that the primary lesion of poliomyelitis occurs in the peripheral ganglia.
Primary invasion through the sympathetics results in initial involvement of the central nervous system at the spinal level; invasion through all the other channels described results in initial involvement of the central nervous system at the level of the brainstem (midbrain, pons, medulla). In neither instance does the level of initial involvement necessarily determine the site of initial paralysis.
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