20 Op. cit.
There is reason to believe, too, that this form of atrophy is one of the consequences of senility—that the tendency to connective-tissue overgrowth which characterizes old age operates to produce, in a way to be presently explained, an atrophy of groups of muscles. In a woman aged seventy, now under my care, the fingers of both hands are clawed—became so inappreciably almost, and the condition is still increasing.
In addition to the above-named causes, long-continued exposure to cold, and especially to the action of very cold water, has been named. Traumatic influences, such as injuries to nerve and muscle, have been called upon to account for localized and progressive atrophy, but these are excluded by our definition from the category of true progressive muscular atrophy.
Cases have also occurred in the course of convalescence. Typhoid fever, rheumatism, measles, scarlet fever, cold during salivation, vaccination, childbed, excessive venery, syphilis,—have all been held responsible for a certain number of cases.
AGE AND SEX.—In examining the literature of acute muscular atrophy it is found that cases are reported at all ages. Thus, Wachsmuth, quoted by Eulenburg, found among 49 cases 13 under the age of fifteen, 8 from fifteen to twenty, 22 from twenty to fifty, and only 6 over fifty years. On the other hand, Roberts—who, following Aran, divides the disease into the general form and partial form—says the latter very rarely falls on individuals under adult age or over fifty, while the average age of the instances of the partial form studied by him was thirty-two years and four months. In 10 instances of the general form the patients were under twelve, and 2 more are reported as children; 1 was said to be sixty-nine and another fifty-four, the average being twenty-eight years and three months. Of Eulenburg's own cases, 7 acquired the disease before the age of ten, 6 before the twentieth year, 2 before the thirtieth, 8 before the fortieth, 5 before the fiftieth, and none later. The latter observer also finds that whenever the disease is hereditary it occurs earlier, usually before the close of the twentieth year. This was certainly not the case in the Farr family, reported by Osler.
I am inclined to believe, especially in the light of Charcot's21 and of Erb's22 recent studies, that the true spinal form of progressive muscular atrophy is a disease of adult life, and that the majority of cases reported as occurring in early life are instances either of what Erb calls the juvenile form of progressive muscular atrophy or of pseudo-hypertrophic paralysis.
21 "Revision nosographique des Atrophies musculaires progressive," Le Progrès méd., No. 10, 1885, i. 314-335.
22 "Ueber die Juvenile Form der Progressive Muskelatrophie und ihre Beziehungen zur sogenannten Pseudohypertrophie," Deutsches Archiv für klin. Med., xxxiv. 1884, S. 467.
As to sex, males predominate. Thus, according to Friedreich's statistics, out of 176 cases but 33 were females, or about 19 per cent. Of Roberts's collection of 99, 84 were males and 15 females. Of 28 cases noted by Eulenburg, 17 were in men and 11 women. This is doubtless owing to the fact that men are subjected to the causes of the disease more than women. For Roberts early noted that women who engage in needlework, washing, and household service are apparently not less liable than men similarly employed, and he found that of those whose labor did not press excessively on any particular sets of muscles females formed even a majority of cases.
Some singular freaks of selection have presented themselves in the matter of sex, particularly in the cases which have been ascribed to hereditation. Thus it will sometimes attack only the male members of a family. A remarkable instance of this was observed by Meryon, in which four sons were attacked and six daughters remained unaffected; and, again, two boys were attacked and two sisters escaped. This may occur also independent of hereditation. Occasionally the reverse takes place, the sisters only being attacked, while the brothers escape.