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Purpura is a condition of red or purple discolored spots on the skin that do not blanch on applying pressure. The spots are caused by bleeding underneath the skin usually secondary to vasculitis or dietary deficiency of vitamin C (scurvy). They measure 0.3–1 cm (3–10 mm), whereas petechiae measure less than 3 mm, and ecchymoses greater than 1 cm. Pupura 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. ==Classification== Purpura are a common and nonspecific medical sign; however, the underlying mechanism commonly involves one of: *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 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.〔(【引用サイトリンク】url=http://www.nejm.org/doi/full/10.1056/NEJMicm1008722 )〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「purpura」の詳細全文を読む スポンサード リンク
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