Purpura is a condition of red or purple discolored spots on the skin that do not blanch on applying pressure. 



Purpura is caused by bleeding underneath the skin secondary to platelet disorders, vascular disorders, coagulation disorders, or other causes.



It is a dermatologic manifestation of localized red blood cell extravasation, typically do the vascular congestion, blood vessel damage, or coagulopathy.



Purpura measures  3–10 mm in size.



Petechiae measure less than 3 mm, and ecchymoses greater than 1 cm.



Purpura is common with typhus meningitis caused by meningococci or septicaemia. 



Meningococcus (Neisseria meningitidis), a Gram-negative diplococcus organism, releases endotoxin when it lyses, activating  factor XII, which causes disseminated intravascular coagulation 



The DIC is what appears as a rash on the affected individual.



It is a common and nonspecific medical sign.



Underlying mechanisms: 



Platelet disorders: 



Primary thrombocytopenic purpura



Secondary thrombocytopenic purpura



Post-transfusion purpura



Vascular disorders:



Microvascular injury, as seen in old age purpura, when blood vessels are more easily damaged



Hypertensive states



Vasculitis, as in the case of Henoch–Schönlein purpura



Coagulation disorders



Disseminated intravascular coagulation 



Scurvy- vitamin C deficiency-defect in collagen synthesis due to lack of hydroxylation of procollagen results in weakened capillary walls and cells






Clumping fibrillary protein deposits caused by Amyloidosis



Cocaine use



Levamisole use



Purpura is a symptom of acute radiation poisoning in excess of 2 Grays of radiation exposure. 



Cases of psychogenic purpura are also described.



Petechial rash is also characteristic of a rickettsial infection.



It is categorized as palpable or non-palpable.



Non-palpable purpura, suggests ITP or disseminated intravascular coagulation or production disorder, while a normal platelet count suggest a functional platelet disorder, blood vessel wall fragility, or impaired flow from obstruction.


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