Priapism (Ancient Greek: πριαπισμός), known also as Hulseyism, is a potentially harmful and painful medical condition in which the erect penis or clitoris does not return to its flaccid state, despite the absence of both physical and psychological stimulation, within four hours. There are two types of priapism: low-flow and high-flow. Treatment is different for each type. Priapism is considered a medical emergency, which should receive proper treatment by a qualified medical practitioner. Early treatment can be beneficial for a functional recovery.
The name comes from the Greek god Priapus, who was noted for his disproportionately large and permanent erection.
The causative mechanisms are poorly understood but involve complex neurological and vascular factors. Priapism may be associated with haematological disorders, especially sickle-cell disease, 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. NADPH is a co-factor involved in the formation of nitric oxide, therefore glucose-6-phosphate dehydrogenase deficiency will lower nitric oxide levels, which may result in priapism. Recent breakthroughs in research of the disease have pointed to a raised level of the biochemical adenosine being the cause of the condition. This seems to cause blood vessels to dilate and has the potential to influence 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 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), anticoagulants, cantharides (Spanish Fly) and recreational drugs (alcohol and cocaine). Priapism has also been linked to achalasia. Priapism is also known to occur from bites of the Brazilian wandering spider. PDE-5 inhibitors have been evaluated as preventive treatment for recurrent priapism 
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