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.
This is common with typhus and can be present with meningitis caused by meningococci or septicaemia. In particular, meningococcus (Neisseria meningitidis), a Gram-negative diplococcus organism, releases endotoxin when it lyses. Endotoxin activates the Hageman factor (clotting factor XII), which causes disseminated intravascular coagulation (DIC). The DIC is what appears as a rash on the affected individual.
Purpura are a common and nonspecific medical sign; however, the underlying mechanism commonly involves one of:
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.
- ^ "UCSF Purpura Module" (PDF).
- ^ Mitchell RS; Kumar V; Robbins SL; Abbas AK; Fausto N (2007). Robbins basic pathology (8th ed.). Saunders/Elsevier. pp. 10–11. ISBN 1-4160-2973-7.
- ^ "Toxic Effects of Levamisole in a Cocaine User". New England Journal of Medicine.
- ^ Anderson JE, DeGoff W, McNamara M (1999). "Autoerythrocyte sensitization (psychogenic purpura): a case report and review of the literature". Pediatric emergency care 15 (1): 47–8. PMID 10069314. doi:10.1097/00006565-199902000-00014.
- ^ 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 Dermatol 32 (7): 521–3. PMID 8340191. doi:10.1111/j.1365-4362.1993.tb02840.x.