PURPURA, a pathological condition in which blood leaves the smaller blood-vessels and is deposited in the tissues in patches, which, if minute, are termed "petechiae," if large, "ecchymoses." The condition depends upon an alteration of the blood itself, particularly the blood-platelets ; coagulation time is prolonged and the plasma often contains haemoglobin that has left the red blood corpuscles owing to disturbance of their normal relations. Probably these modifications act on the endothelial walls of the capillaries and venules and lead to changes in them also. In the main the haemorrhages constituting purpura occur beneath free surfaces such as skin, mucous and serous membranes and are there most visible but they also occur in the substance of organs and bleeding may occur in dangerous quantity from nose, mouth, bowel, kidney, etc. Blood effused into the tissues undergoes sub sequent changes like those seen in a receding bruise.
The clinical causes of purpura are various. Following snake bite, or the administration of such drugs as copaiba and bella donna, or the onset of jaundice, it seems to be caused by the action of a chemical poison and probably the same is true when it accompanies acute infectious fevers (e.g., severe forms of scar
let fever and small-pox), heart disease, especially ulcerative endo carditis, and some forms of Bright's disease. It is a short step from this to invoking a chemical poison of microbial origin in those forms of purpura which are associated with articular or rheumatic pain or even constitute apparently the substantive dis ease, but of this there is, as yet, no proof. From the fact that haemorrhage is present in both instances purpura has many clin ical resemblances to haemophilia (q.v.) and the two morbid con ditions may often have been confused. Probably similar blood changes occur in both, but they appear to be distinct diseases.
Treatment is that of any underlying condition, but astringents (such as iron, gallic acid), may be required in severe cases. Sir A. Wright holds that in all cases of purpura the coagulation time should be determined and if prolonged, calcium should be given internally. In severe haemorrhage adrenalin is often useful.
See H. L. Tidy, "The Haemorrhagic Diathesis," Brit. Med. hi.