Purpura is the appearance of 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. Purpura measure 0.3–1 cm, 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 meningococcal meningitis
or septicaemia. In particular, meningococcus, a Gram-negative diplococcus organism, releases
endotoxin when it lyses. Endotoxin activates the Hageman factor, which causes disseminated
intravascular coagulation. The DIC is what appears as a rash on the affected individual.
Classification Purpura are a common and nonspecific medical
sign; however, the underlying mechanism commonly involves one of the following:
Platelet disorders Primary thrombocytopenic purpura
Secondary thrombocytopenic purpura Post-transfusion purpura
Vascular disorders Microvascular injury, as seen in senile purpura,
when blood vessels are more easily damaged Hypertensive states
Deficient vascular support Vasculitis, as in the case of Henoch-Schönlein
purpura
Coagulation disorders Disseminated intravascular coagulation
Scurvy - defect in collagen synthesis due to lack of hydroxylation of procollagen results
in weakened capillary walls and cells
Meningococcemia 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
are 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.
There are also cases of psychogenic purpura described in the medical literature, some
claimed to be due to "autoerythrocyte sensitization". Other studies suggest the local activity of
tPA 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. See also
Bruise, which is a hematoma caused by trauma Petechia, which is a small type of hematoma
Ecchymosis, which is a large type of hematoma Purpura secondary to clotting disorders
Food-induced purpura Purpura haemorrhagica in horses
Pigmented purpuric dermatosis Schamberg disease
References ^ "UCSF Purpura Module".
^ Mitchell RS; Kumar V; Robbins SL; Abbas AK; Fausto N. Robbins basic pathology. 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. "Autoerythrocyte
sensitization: a case report and review of the literature". Pediatric emergency care
15: 47–8. doi:10.1097/00006565-199902000-00014. PMID 10069314.
^ Lotti T, Benci M, Sarti MG, Teofoli P, Senesi C, Bonan P, et al.. "Psychogenic purpura with
abnormally increased tPA dependent cutaneous fibrinolytic activity". Int J Dermatol 32:
521–3. doi:10.1111/j.1365-4362.1993.tb02840.x. PMID 8340191.
External links Evaluating the Child with Purpura from American
Academy of Family Physicians