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Priapism (〔''OED'' 2nd edition, 1989 as .〕〔(Entry "priapism" ) in ''(Merriam-Webster Online Dictionary )''.〕) is a potentially painful medical condition in which the erect penis does not return to its flaccid state, despite the absence of both physical and psychological stimulation, within four hours. Priapism is considered a medical emergency, which should receive proper treatment by a qualified medical practitioner. There are two types of priapism: low-flow and high-flow; 80% to 90% of clinically presented priapisms are low-flow disorders.〔PRIAPISM – ETIOLOGY, PATHOPHYSIOLOGY AND MANAGEMENT, C. VAN DER HORST, HENRIK STUEBINGER, CHRISTOPH SEIF, DIETHILD MELCHIOR, F.J. MARTÍNEZ-PORTILLO, K.P. JUENEMANN; http://www.scielo.br/pdf/ibju/v29n5/18554.pdf〕 Low-flow involves the blood not adequately returning to the body from the penis. High-flow involves a short-circuit of the vascular system partway along the penis. Treatment is different for each type. Early treatment can be beneficial for a functional recovery. Not all sources give four hours as the guideline for priapism occurring: "The duration time of a normal erection before it is classifiable as priapism is still controversial. Ongoing penile erections for more than 6 hours can be classified as priapism."〔 The name comes from the Greek god Priapus (), a fertility god often represented with a disproportionately large and permanent erection. ==Causes== The causative mechanisms are poorly understood but involve complex neurological and vascular factors. Priapism may be associated with haematological disorders, especially sickle-cell disease, sickle-cell trait, and other conditions such as leukemia, thalassemia, and Fabry's disease, and neurologic disorders such as spinal cord lesions and spinal cord trauma (priapism has been reported in hanging victims; see death erection). Priapism may also be associated with glucose-6-phosphate dehydrogenase deficiency, which leads to decreased NADPH levels. NADPH is a co-factor involved in the formation of nitric oxide, which may result in priapism. Raised levels of adenosine may also contribute to the condition by causing blood vessels to dilate, thus influencing blood flow into the penis. Sickle cell disease often presents special treatment obstacles. Hyperbaric oxygen therapy has also been used with success in some patients. Priapism is also found to occur in extreme cases of rabies. Priapism can also be caused by reactions to medications. The most common medications that cause priapism are intra-cavernous injections for treatment of erectile dysfunction (papaverine, alprostadil). Other groups reported are antihypertensives, antipsychotics (e.g., chlorpromazine, clozapine), antidepressants (most notably trazodone), anti-convulsant and mood stabilizer drugs such as sodium valproate, anticoagulants, cantharides (''Spanish Fly'') and recreational drugs (alcohol, heroin and cocaine). Priapism has also been linked to achalasia. Priapism is also known to occur from bites of the Brazilian wandering spider and the black widow spider.〔(【引用サイトリンク】title=Spider Venom for Erectile Dysfunction? )〕 PDE-5 inhibitors have been evaluated as preventive treatment for recurrent priapism. 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「Priapism」の詳細全文を読む スポンサード リンク
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