In the course of purpura there is frequently observed, more especially in purpura simplex, a wheal-like arrangement of the eruption—such, indeed, as occurs in urticaria. The term purpura urticans has been given to this sub-variety, which may or may not be accompanied by itching. Scheby-Buch has suggested that the urticaria may, with more propriety, be attributed to the gastric disturbances that so often accompany the forms of purpura presenting it.7 The wheals are usually seen upon the lower extremities, but may appear elsewhere. A considerable degree of oedema may be present, particularly in lax tissue, such as that of the scrotum, eyelids, etc.
7 Deutsche Arch. f. Klin. Med., B. xiv. p. 490.
Purpura papulosa (lichen lividus, Willan) is a form of purpura where, in the midst of ecchymoses, livid papules appear. These probably depend upon a large amount of hemorrhage occurring within a limited space, most often surrounding the orifices of hair-follicles, because these are supplied with a capillary network that comes directly from the deeper layer.8 They are formed most abundantly on the legs of scrofulous, cachectic persons who have purpura. Care must be taken to distinguish this form of purpura from erythema multiforme and erythema nodosum, where blood is usually extravasated secondarily into the tissues. Those cases only where the purpura is primary should be recognized as purpura papulosa.
8 Hebra, Skin Diseases, New Syd. Soc. Transact., ii. p. 425.
The purpuric effusion appears to act as an irritant upon the tissues, and to excite inflammation. Gangrene of the mucous coat of the intestines has resulted from extensive hemorrhagic extravasations, and from a similar cause cutaneous gangrene has been known. These complications, however, are rare.
ETIOLOGY.—The immediate causes of purpura are quite unknown. Both sexes and persons of every age are affected by it. While it is most often seen in debilitated subjects, those in vigorous health possess no immunity. It has often been observed during convalescence from other maladies. It cannot be said that those who are miserably clothed, fed, and lodged are especially predisposed to attacks of purpura. Between purpura and hæmophilia, etiologically, there are many points of difference. Purpura is not hereditary, nor is there a purpuric diathesis in the strict sense of the term. Some persons, indeed, seem to possess a predisposition to the disease, and some authors claim for purpura rheumatica a distinct annual type. This, however, is not at all certain.
Recently it has been claimed that purpura hæmorrhagica depends upon the presence of a minute organism in the blood. Petrone9 injected blood drawn from patients with this disease under the skin of rabbits, producing widely-distributed hemorrhages. In the blood of these individuals and of the injected rabbits micrococci and bacilli were detected. Watson Cheyne10 also describes a plugging of the capillaries with bacilli. These were 1/7700 of an inch in length and 1/20000 of an inch in diameter, and were arranged in colonies. In another case there were found micrococci arranged in chains. These swarmed in the capillaries and some larger vessels, and sometimes completely blocked them. Although an origin in infection has thus been claimed for purpura hæmorrhagica, the fact that more than one variety of micro-organism was observed cannot fail to excite suspicion of, possibly, erroneous observation.
9 Lo Sperimentale, 51, 1883.
10 Lancet, i., 1884, 344.
PATHOLOGY.—In the foregoing description those extravasations of blood due to simple mechanical violence, as from flea-bite, and sudden increase of blood-pressure, as in the effort of coughing in whooping cough, also from the deleterious influence exerted upon the blood-vessels and blood by certain drugs, the specific fevers, Bright's disease, and the like, have been excluded. Only those have been considered where the effusion of blood seemed to occur spontaneously, and the symptoms to result from some peculiar but not understood morbid process. The hemorrhage is but a symptom; the process by which it is brought about depends upon some change in the blood or blood-vessels. We do not know what these subtle changes are. The blood of purpuric patients has been carefully examined, but, with the exception above mentioned, no definite changes have been discovered. Immermann11 found during the first stage of the disease the blood-corpuscles perfectly normal in appearance, the white corpuscles subsequently slightly exceeding the red in number—a simple result of copious hemorrhage. No stated chemical changes in the blood are known in purpura, nor is it known how the blood escapes from the vessels. It undoubtedly escapes through alterations in the vascular wall, but it is also true that red blood-corpuscles, as well as the pale ones, may find their way in considerable numbers through the unruptured wall of the vessels, per diapedesin, as was first suggested by Velpeau, but definitely determined by Stricker. The causes of this migration are obscure. Immermann12 asserts that a fatty degeneration of the vascular tissues and of the muscles takes place. This, however, is manifestly a result of the loss of blood, and not its cause. Dr. Wilson Fox13 found extensive albuminoid disease of the muscles and capillaries of the skin; but the albuminoid degeneration involved several organs of a patient with syphilis, and the purpura was certainly secondary to the morbid conditions. Rigal and Cornil14 think that the hemorrhages are a result either of sympathetic irritation or of diminished action of the vaso-motor centre. It is indeed altogether likely that the cause will ultimately be found to reside in the vaso-motor system.