Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases are ischemic. Ischemic priapism is generally painful while nonischemic priapism is not. In ischemic priapism, most of the penis is hard; however, the glans penis is not. In nonischemic priapism, the entire penis is only somewhat hard. Very rarely, clitoral priapism occurs in women.Sickle cell disease is the most common cause of ischemic priapism. Other causes include medications such as antipsychotics, SSRIs, blood thinners and prostaglandin E1, as well as drugs such as cocaine. Ischemic priapism occurs when blood does not adequately drain from the penis. Nonischemic priapism is typically due to a connection forming between an artery and the corpus cavernosum or disruption of the parasympathetic nervous system resulting in increased arterial flow. Nonischemic priapism may occur following trauma to the penis or a spinal cord injury. Diagnosis may be supported by blood gas analysis of blood aspirated from the penis or an ultrasound.Treatment depends on the type. Ischemic priapism is typically treated with a nerve block of the penis followed by aspiration of blood from the corpora cavernosa. If this is not sufficient, the corpus cavernosum may be irrigated with cold, normal saline or injected with phenylephrine. Nonischemic priapism is often treated with cold packs and compression. Surgery may be done if usual measures are not effective.
A genome-wide association study on Brazilian patients with sickle cell disease identified four single nucleotide polymorphisms in LINC02537 and NAALADL2 significantly associated with priapism.Other conditions such as Fabrys disease, as well as neurologic disorders such as spinal cord lesions and spinal cord trauma (priapism has been reported in people who have been hanged; see death erection). Priapism can also be caused by reactions to medications. The most common medications that cause priapism are intra-cavernous injections for the treatment of erectile dysfunction (papaverine, alprostadil). Other medication 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) have been associated. Priapism is also known to occur from bites of the Brazilian wandering spider. High-flow priapism
Causes of high-flow priapism include:

blunt trauma to the perineum or penis, with laceration of the cavernous artery, which can generate an arterial-lacunar fistula. Anticoagulants (heparin and warfarin). Antihypertensives (i.e., hydralazine, guanethidine and propranolol). Hormones (i.e., gonadotropin releasing hormone and testosterone). Diagnosis
The diagnosis is often based on the history of the condition as well as a physical exam.Blood gas testing the blood from the cavernosa of the penis can help in the diagnosis. If the low-flow type of priapism is present, the blood typically has a low pH, while if the high-flow type is present, the pH is typically normal. Color Doppler ultrasound may also help differentiate the two.