These figures show that the male sex is somewhat oftener attacked than the female. But the source of this difference eludes us. Of Byrom Bramwell's cases, 43 per cent, were male; 56 per cent, female.
Dejerine has asserted that a neuropathic disposition is an important etiological factor in the development of acute poliomyelitis. Wickman, Medin and Leegaard, however, could not substantiate this assertion.
Even when I elicited proof of a neurotic tendency in a patient's family, I could not attribute any causal significance to it. Ed. Muller also calls attention to the fact that in his experience the children affected by acute poliomyelitis were free from neuropathic taint, and, as a rule, were physically and mentally normal. Johannessen, however, found various mental diseases among the families in several of his cases.
Occasionally, infantile paralysis has been reported in those whose relatives (uncle and aunt) had previously been affected (Wickman, Furntratt). Leegaard attributes a certain importance to chills and reports strikingly numerous cases which followed exposure to cold and wet. Perhaps, however, we ought rather to consider such exposure as belonging to the general condition under which the people live. It is difficult to determine if over-exertion is a predisposing cause, but I am convinced that at least once the disease has begun, over-exertion has an unfavorable influence upon its further course.
Hochhaus and others have occasionally observed the disease to follow vaccination. This association is most probably accidental.
Finally, an acute atrophic paralysis may rarely arise from a variety of causes other than the virus which produces Heine-Medin's disease. A few cases are recorded of acute poliomyelitis probably due to syphilis; e. g., J. Hoffmann's case. Some may be classed as cases of partial transverse myelitis. Typical Heine-Medin's disease has been observed to develop in a case of an existing luetic infection. Injury may cause a hematomyelia localized to the anterior horns, and thus simulating acute poliomyelitis (Beyer); but the history and onset serve readily to identify this condition.
