Purpura (from Latin: purpura, meaning "purple") are red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin usually secondary to vasculitis or dietary deficiency of vitamin C (scurvy). Purpura measure 0.3–1 cm (3–10 mm), whereas petechiae measure less than 3 mm, and ecchymoses greater than 1 cm.
Cocaine use with concomitant use of the one-time chemotherapy drug and now veterinary deworming agent levamisole can cause purpura of the ears, face, trunk, or extremities, sometimes needing reconstructive surgery. Levamisole is purportedly a common cutting agent.
Decomposition of blood vessels including purpura is a symptom of acute radiation poisoning in excess of 2 Grays of radiation exposure. This is an uncommon cause in general, but is commonly seen in victims of nuclear disaster.
Cases of psychogenic purpura are also described in the medical literature, some claimed to be due to "autoerythrocyte sensitization". Other studies suggest the local (cutaneous) activity of tissue plasminogen activator can be increased in psychogenic purpura, leading to substantial amounts of localized plasmin activity, rapid degradation of fibrin clots, and resultant bleeding. Petechial rash is also characteristic of a rickettsial infection.
^Lotti T, Benci M, Sarti MG, Teofoli P, Senesi C, Bonan P et al. (1993). "Psychogenic purpura with abnormally increased tPA dependent cutaneous fibrinolytic activity". Int J Dermatol32 (7): 521–3. doi:10.1111/j.1365-4362.1993.tb02840.x. PMID8340191.CS1 maint: Explicit use of et al. (link)