Purpura

Purpura (from purpura, meaning "purple") 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. 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 meningococcal meningitis or septicaemia. In particular, meningococcus, a Gram-negative diplococci organism, releases endotoxin when it lyses. Endotoxin activates the Hageman factor (clotting factor XII), which causes disseminated intravascular coagulation. The DIC is what appears as a rash on the affected individual.

Classification
Purpura is a common and nonspecific medical sign; however, the underlying mechanism commonly involves one of the following:


 * Platelet disorders (Thrombocytopenic purpura)
 * Primary thrombocytopenic purpura
 * Secondary thrombocytopenic purpura
 * Post-transfusion purpura
 * Vascular disorders (Nonthrombocytopenic purpura)
 * Microvascular injury, as seen in senile (old age) 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 (DIC)
 * Scurvy (vitamin C deficiency) - defect in collagen synthesis due to lack of hydroxylation of procollagen. It results in weakened capillary walls and cells.
 * Meningococcemia

There are also cases of psychogenic purpura described in the medical literature, some claimed to be due to "autoerythrocyte sensitization." Other studies suggest, that local (cutaneous) 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.