Priapism

Priapism is an involuntary, prolonged erection unrelated to sexual stimulation and unrelieved by ejaculation.

This condition is a true urologic emergency, and early intervention allows the best chance for functional recovery.

It is defined by erections of greater than 4 hrs duration.

Based on subtypes of priapism, signs and symptoms include:

• Ischemic (veno-occlusive, low flow) priapism is a nonsexual, persistent erection characterized by little or no cavernous blood flow and abnormal cavernous blood gases (hypoxic, hypercarbic, and acidotic). The corpora cavernosa are rigid and tender to palpation. Patients typically report pain. A variety of etiologic factors may contribute to the failure of the detumescence mechanism in this condition. Ischemic priapism is an emergency.
• Resolution of ischemic priapism is characterized by the penis returning to a flaccid, nonpainful state. However, in many cases, persistent penile edema, ecchymosis and partial erections can occur and it may mimic unresolved priapism. Resolution of priapism can be verified by measurement of cavernous blood gases or blood flow measurement by color duplex ultrasonography.
• Nonischemic (arterial, high flow) priapism is a nonsexual, persistent erection caused by unregulated cavernous arterial inflow. Cavernous blood gases are not hypoxic or acidotic. Typically the penis is neither fully rigid nor painful. Antecedent trauma is the most commonly described etiology. Nonischemic priapism does not require emergent treatment.
• Resolution of nonischemic priapism is characterized by a return to a completely flaccid penis.
• Stuttering (intermittent) priapism is a recurrent form of ischemic priapism in which unwanted painful erections occur repeatedly with intervening periods of detumescence. This historical term identifies a patient whose pattern of recurrent ischemic priapism encourages the clinician to seek options for prevention of future episodes.

Priapism can be idiopathic or can be secondary caused by a variety of diseases, conditions, or medications.

In the United States, the most common cause of priapism in the adult population involves agents used to treat erectile dysfunction. Internationally, most cases are idiopathic.

The most common cause of priapism in the pediatric population is sickle cell disease (SCD), which is responsible for 65% of cases. Leukemia, trauma, and idiopathic causes are the causes in 10% of patients. Pharmacologically induced priapism is the etiology in 5% of children.

Among the secondary causes of low-flow priapism are the following thromboembolic/hypercoagulable states:

• Sickle cell anemia
• Thalassemia
• Fabry disease
• Dialysis
• Vasculitis
• Fat embolism

Neurologic diseases that can result in low-flow priapism include the following:

• Spinal cord stenosis
• Autonomic neuropathy and cauda equina compression

Neoplastic diseases (metastatic to the penis or obstructive to venous outflow) that can result in low-flow priapism include the following:

• Prostate cancer
• Bladder cancer (highest risk)
• Hematologic cancer (leukemia)
• Renal carcinoma
• Melanoma

Pharmacologic causes of low-flow priapism include the following:

• Intracavernosal agents - Papaverine, phentolamine, prostaglandin E1
• Intraurethral pellets (ie, medicated urethral system for erection with intracavernosal prostaglandin E1)
• Antihypertensives - Ganglion-blocking agents (eg, guanethidine), arterial vasodilators (eg, hydralazine), alpha-antagonists (eg, prazosin), calcium channel blockers
• Psychotropics - Phenothiazine, butyrophenones (eg, haloperidol), perphenazine, trazodone, selective serotonin reuptake inhibitors (eg, fluoxetine, sertraline, citalopram)
• Anticoagulants - Heparin, warfarin (during rebound hypercoagulable states)
• Recreational drugs - Cocaine
• Hormones - Gonadotropin-releasing hormone (GnRH), tamoxifen, testosterone, androstenedione for athletic performance enhancement
• Herbal medicine - Ginkgo biloba with concurrent use of antipsychotic agents
• Miscellaneous agents - Metoclopramide, omeprazole, penile injection of cocaine, epidural infusion of morphine and bupivacaine 

High-flow priapism may result from the following forms of genitourinary trauma:

• Straddle injury
• Intracavernous injections resulting in direct cavernosal artery injury

Rare causes of priapism include the following:

• Amyloidosis (massive amyloid infiltration)
• Gout
• Carbon monoxide poisoning
• Malaria
• Black widow spider bites
• Asplenia
• Fabry disease (rare association, occasionally noted to be priapism of the high-flow type)
• Vigorous sexual activityMycoplasma pneumoniae infection (mechanism is thought to be a hypercoagulable state induced by the infection)

Diagnostic work up for priapism includes following:

• CBC: To determine if the patient has anemia, luekocytosis, thrombocytosis, or may be undiagnosed leukemia.
• For patients suspected of sickle cell disease, the diagnostic tests include; CBC, reticulocyte count, haemoglobin S determination, blood type.
• Measurement of plasma thromboplastin or activated partial thromboplastin time to determine coagulation status may be useful in case of emergent need to operate the patient.
• Penile blood gas (PBG) test results allow differentiation between high- and low-flow priapism. Low-flow PBG findings may include a pH of less than 7.0, a PCO2 of greater than 60 mm Hg, and a PO2 of less than 30 mm Hg. Variation depends on the duration of the episode. High-flow PBG findings should reflect normal arterial values. 
• Color flow penile Doppler imaging is the investigation of choice. Ultrasonography can help to identify and locate fistulas.
• In patients with high-flow priapism, selective penile angiography may be required in order to identify the site of the fistula, or to confirm the location of a fistula identified by ultrasound. The fistula can then be closed by embolization. 
• Perform chest X-Ray or CT scan to identify a malignant and possible metastatic cause.

Treatment methods for priapism include:

• Medical advice should be sought immediately for cases of erection beyond four hours. In sickle-cell anaemia guidelines recommend a conservative treatment approach of prompt initial rehydration. For others, orally administered pseudoephedrine and other sympathetomimmetic drugs may be effective, pseudoephedrine being an alpha-agonist agent that exerts a constriction effect on smooth muscle of corpora cavernosum, that in turn facilitates venous outflow. Otherwise, the therapy at this stage is to aspirate blood from the corpus cavernosum under local anaesthetic. If this is still insufficient, then intracavernosal injections of phenylephrine are administered.
• Terbutaline being a beta-2 agonist causes smooth muscle relaxation; in priapism it probably acts by relaxation of the stretched corporeal smooth muscles, or increasing permeability of erectile cavernous tissue permitting easy flow of fluid from sinusoids into the venous system. In priapism, it was suggested to be administered orally.
• Methylene blue is used intracavernously to treat priapism, but it should not be used in treatment of recurrent priapism or fibrosis because it can induce penile necrosis. Temporary blue discoloration of the penis is also of concern.
• If aspiration fails and tumescence recurs, surgical shunts are next attempted. This attempt to reverse the priapic state by shunting blood from the rigid corpora cavernosa into the corpus spongiosum (which contains the glans and the urethra). Distal shunts are the first step, followed by more proximal shunts.
• As the complication of shortened, indurated and non-erectile penis is high in prolonged priapism, early penile prosthesis implantation can be performed. Apart from early resumption of sexual activity, early implantation can avoid the formation of dense fibrosis and hence a shortened penis.

There are several complications associated with priapism.

Because ischemic priapism causes the blood to remain in the penis for unusually long periods of time, the blood becomes deprived of oxygen and can cause damage to the penile tissue itself.

Should the penile tissue become damaged, it can further result in erectile dysfunction or disfigurement of the penis.

In extreme cases, if the penis suffers from severe vascular disease, the priapism can result in penile gangrene.