The fact that the disease begins in the extensor muscles of the lower extremities is probably to be explained by the rapid development of these muscles during early childhood, and by the functional strain imposed on them during the effort of learning to walk. It is thus really analogous to the début of progressive atrophy in the muscles of the hands of adults—the muscles whose functional activity is the most incessant and the most complex during adult life.
The preponderance of the disease in males remains unexplained, unless it be that the greater extent of muscular development in the male necessitates a greater intensity of developmental force for the muscles, whose deficiency, therefore, would earlier be made manifest.
DIAGNOSIS.—The diagnosis of pseudo-hypertrophic paralysis can never be difficult in typical cases and at an advanced period of the disease. During the early period the diagnosis rests on the gradual diminution of force in the lower extremities, without atrophy or with apparently excellent development of their muscles; the straddling of the legs, lordosis, and lateral oscillation, all at first slight, but constantly becoming more and more emphasized; the peculiar method of rising by placing the hands on the knees and then gradually climbing up the thighs. In the second period the enlargement of the calf or other muscles of the lower limbs, in the third the extension of the paresis to the upper extremities, associated with wasting of the pectorals and usually some of the extensors of the back, confirm beyond question the diagnosis. This may be further established by examination of small fragments of muscular fibre removed by means of the harpoon or trocar, and the repeated examinations, which serve, moreover, to mark the progress of the disease.
Few diseases require to be differentiated. One very rare disease that might be confounded with pseudo-hypertrophy is the infantile form of progressive muscular atrophy. This is distinguished from the ordinary form of atrophy by beginning in the muscles of the face,86 especially the orbicularis oris, from whose defective contractility the lips become thick and motionless. The morbid process then progresses downward, and is thus in notable contrast with that of pseudo-hypertrophy, which invariably begins in the lower limbs and extends upward, invading the face only by exception.
86 Duchenne has seen seventeen cases of this disease.
It is probably after the establishment of talipes equinus and of flexions at the knee- or hip-joint that pseudo-hypertrophy would be most liable to be confounded with infantile atrophic paralysis. In the latter, however, the talipes is much more rarely double, and, if existing, is usually complicated with varus. At an advanced stage of pseudo-hypertrophy the enlargement of the calf is apt to be confined to its upper part, and the retraction of the lower half simulates atrophy, even when this has not really set in. At this stage, moreover, the thighs and gluteal regions are usually atrophied, so that the resemblance to an atrophic paralysis may be considerable. This may be still further increased in those rare cases of extensive polio-myelitis, where paralysis of one or more of the upper extremities coincides with lumbar paraplegia. It is extremely rare, however, that both arms are paralyzed and atrophied,87 while this is the rule, with approximative symmetry, in pseudo-hypertrophy. In the latter disease, moreover, there are paralysis and atrophy of the muscles of the trunk and abdomen, which is scarcely ever seen, and never to the same extent, in atrophic paralysis. The reflex excitability is lost in the latter disease, as also the faradic; the latter, often intact in pseudo-hypertrophy, rarely is quite abolished. Finally, the history of the case is generally decisive: gradual development in the one, sudden onset, with immediate maximum intensity of paralysis, in the other; primitive wasting of the paralyzed muscles in the spinal paralysis, enlargement preceding the atrophy in the pseudo-hypertrophic paralysis.
87 A patient described by Eulenburg was affected by such general paralysis, but recovered after five months' treatment.
Rachitis, with its frequent polysarcia and paretic gait, might sometimes lead to a suspicion of muscular pseudo-hypertrophy, as, conversely, the earlier symptoms of the latter disease may be erroneously referred to rachitis. The error is all the more facile because children afflicted with pseudo-hypertrophy are not unfrequently rachitic, and the symptoms of specific paralysis and muscular sclerosis may easily seem to deepen out of those of muscular inertia and subcutaneous fat which are due to the nutritive diathesis. The consistency of the enlarged limbs is, however, different—soft and flabby in rachitis, hard, even stony, in pseudo-hypertrophy. When in the latter the subcutaneous fat is atrophied instead of increased, the muscles seem to make hernial protrusions through the emaciated skin.
Congenital cerebral disease, due to intra-uterine lesion, causes imperfect walking, and even contraction of the calf-muscles, which may simulate the analogous symptoms of pseudo-hypertrophic paralysis. But the trunk is bent straight forward, and not bent in lordosis; the lower extremities tend to cross in spastic paraplegia; there is no lateral oscillation of the trunk, and the faradic contractility is always preserved. The progress of the diseases suffices to decide all doubts.
TREATMENT.—The excessively bad prognosis of pseudo-hypertrophic paralysis may be inferred from the foregoing description. Duchenne claims to have had two cases brought to him at the early stage of the disease. The first (Obs. 9) was a boy attacked at the age of seven and a half with paresis of the lower extremities. He soon began to walk with a straddling gait, lordosis, and lateral oscillation. Thirty-four months later some enlargement of the calves was noticed, but the disease remained stationary for six months, when the patient was brought to Duchenne. He was treated by hydro-therapeutics, massage, and faradization of the affected muscles. Cure was complete in six months.