Purpura rheumatica presents, as has been shown, many points of resemblance to erythema multiforme and erythema nodosum. The mild fever, the joint-pains, the extravasations of the latter affections, are much like the symptoms of this form of purpura. The nodular, inflamed, tender condition of the lesions, their location--frequently upon the extensor surfaces of the extremities--their course and duration, usually serve to identify erythema nodosum, while with erythema multiforme it is usually not difficult to observe its essentially inflammatory character. Scheby-Buch has shown the difficulties often opposed to the differentiation of purpuric lesions and ecchymoses due to violence.[15] Where the petechial eruption of purpura simplex is well marked, where the internal hemorrhages of purpura hæmorrhagica are copious, the inquiries of the observer will usually lead him to correct conclusions. Where the {193} ecchymoses are larger and upon exposed parts of the body, the diagnosis from the lesions alone becomes impossible, and due consideration of all concomitant circumstances is essential. It should be remembered that in purpura very slight violence may call forth extensive ecchymosis. This circumstance has important medico-legal bearings. [Footnote 15: _Viertelj. f. Dermatol. und Syph._, 1879, p. 99.] PROGNOSIS.--Purpura usually terminates favorably. Its course runs from two to six weeks, rarely longer. Relapses and remissions are frequent. Purpura simplex is of very little gravity, and need excite little apprehension. Purpura rheumatica almost always ends in recovery; fatal terminations, however, have been known. Purpura hæmorrhagica is of much more serious import. Even here, however, though the patient may fall into profound debility from loss of blood, recovery is the rule, the symptoms gradually diminishing in severity until health becomes re-established. In fatal cases death ensues after prolonged and profuse losses of blood. Purpura may subside after a single outbreak or many relapses, and recrudescences may occur extending through months. Anæmia may persist long after the disappearance of purpuric symptoms. A tendency to purpura may be shown at irregular intervals for years, and even throughout life.