With regard to the pathology of the disease, the fault has been sup posed to lie in some alteration of nutrition in the coats of the capillaries and smaller blood-vessels, so that they rupture readily under the pressure of the blood. This explanation may be a sufficient one when the purpura occurs in a cachectic subject, but it cannot apply to the sudden tendency to hemorrhages often manifested by a child whose health had been pre viously satisfactory. Henoch suggests that in these cases the cause of the effusion may be a vaso-motor neurosis which gives rise to stasis in the blood, rupture of the wall of the capillaries, or migration of the blood globules from paralytic dilatation of the smallest vessels.
Symptonis.—The spots may appear quite suddenly without previous signs of ill-health. Often, however, they are preceded by more or less aching of the limbs, slight feverishness, thirst, and symptoms of indiges tion. The child has no appetite and is unwilling to exert himself, crying if obliged to walk, and complaining constantly of feeling tired. In some cases the appearance of the purpuric rash follows an attack of vomiting and diarrhcea. The spots are circular and of a brick-red or deep purple colour. They are not elevated above the surface, and pressure does not cause them to disappear. In size they vary from a pin's head to the diameter of half an inch or more, and their outline is distinctly defined. They may be so closely set as to be confluent. This is especially common about the instep and ankles. Often they are accompanied by marks like bruises due to extravasation into the subcutaneous tissue. These are bluish discolourations without defined margin, and may be accompanied by some swelling. They appear to be sometimes the consequence of in significant injuries, for a gentle pinch or feeble blow will produce them. The purpuric spots come out in successive crops, and each, after going through the ordinary changes of colour peculiar to such hemorrhages, disappears in the course of a few days. At times the skin will be found to be nearly clear ; then another crop is discovered and the surface is thickly studded with them as before. They are usually most numerous on the limbs, but are found besides on the trunk, and sometimes, although rarely, on the face. Mixed up with the true purpuric spots may be wheals of urticaria, little patches of erythema papulatum or erythema noclosum, and occasionally blebs arise filled with bloody serum. Inspec tion of the mouth will also often discover minute haemorrhagic extravasa tions into the mucous membrane of the lips and cheeks.
In the more acute form of the disease, when the general health has been previously satisfactory, the purpuric spots may be accompanied by cedematous swelling. The limbs then feel unusually firm and full and pit on pressure. Unless haemorrhage occurs from the urinary passages there is no albuminuria.
A healthy little girl, aged five years, began to lose her appetite and complain of pains in the legs and knees. She was unwilling to take ex
ercise, and after walking for a short distance would say that her legs ached and ask to be carried up-stairs. These symptoms continued for two or three weeks without improvement. The child then became slightly feverish, her knees swelled, and purpuric spots appeared on the lower part of the body and on the legs. When seen on the sixth day the child looked well in the face and seemed cheerful. The spots were numerous on the lower limbs and varied from a pea to a fourpenny bit in size. They were brick-red in colour with a well-defined outline, and did not disappear on pressure with the finger. In addition to these spots there were larger patches, like bruises, of a greenish or yellowish colour. Both legs were uniformly swollen and felt very firm. They pitted distinctly on firm pressure. The knees were not swollen or tender at this time, but were said to have been very tender and painful. The skin covering the pop liteal spaces was much ecchymosed. There had been no bleeding from the nose or other mucous tract. The heart-sounds were healthy. There was no albumen in the urine.
The pains in the limbs usually continue after the spots have appeared, but subside in a few days. A return of the pain is sometimes found to precede the eruption of each successive crop of spots. The number of the crops varies. Sometimes there is only one. Usually, however, they are more numerous. Exercise seems to encourage the haemorrhages, and rest is therefore an important element in the treatment. In the simple form the disease is usually at an end in from one to three weeks.
In simple purpura the extravasations are limited to the skin, but in the more severe form, called hcemorrhagic purpura, effusions of blood are noticed from other parts. The nose bleeds, and the hinorrhage may be so copious that it has to be arrested by mechanical means. Blood may be also discharged from the eyelids, the gums, the ears, the lungs, the stomach, the bowels, and the kidneys. Hfematuna is a common conse quence of hemorrhagic purpura, and the amount of blood may be so copious from this source that the urine passed is of a deep red colour. The renal licemorrhage often occurs in one gush and then ceases entirely for a time, so that two successive discharges from the bladder may be of quite different characters—the first blood red, the second perfectly limpid and normal in appearance. Still, even if there be no naked-eye signs of blood in the water, the microscope will sometimes detect red corpuscles in the deposit. Haemorrhage from the bowels is seen as black clots at the bottom of the chamber-pan. It is rarely copious. Its appearance may be preceded by severe abdominal pain, which ceases when the blood is dis charged from the bowels. Sometimes colicky pain occurs without being followed by intestinal hemorrhage.