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- Penile (or less common clitoral) erection lasting for >4 hours and unrelated to sexual stimulation or arousal
- Classified into three types: ischemic, nonischemic, and stuttering:
- Ischemic (low-flow, veno-occlusive) priapism, associated with ischaemia of the corpora cavernosa, is prolonged and painful and requires urgent clinical intervention.
- Nonischemic (high-flow, arterial) priapism is less common and often painless, could be related to prior trauma, and does not require urgent treatment.
- Stuttering priapism (recurrent, ischemic) is episodic, short-lived, and self-limited.
- Malignant priapism is a rare condition resulting most commonly from penile metastases from primary bladder, prostatic, rectosigmoid, and renal tumors.
- System(s) affected: reproductive, vascular
- Functional impairment: neurophysiological, sexual, psychosocial (quality of life) (1)
- In children, nearly all priapism is caused by either sickle cell disease (SCD) (65% of cases) or leukemia, idiopathic, penile trauma (e.g., post circumcision), or illicit drugs (up to 35% of cases) and typically begins to occur during adolescent years.
- Neonatal priapism is also rare and last >4 hours in newborn infants occurring in the first few days of life and lasts 2 to 12 days (2).
- Prevalence: In the United States, one study estimates 1,868 to 2,960 cases of priapism each year, with increasing incidence related to nonhematologic causes from 1998 to 2006.
- Age: There has been an age shift since 2008 toward men in their 40s. The incidence doubles in men aged >40 years (2.9 vs. 1.5/100,000 person-years).
- Race: 61.1% black (correlated with incidence of SCD), 30% white, 6.3% Hispanic
- Anatomy and physiology:
- The penis consists of three longitudinally oriented corpora: two dorsolaterally paired corpora cavernosa that are responsible for penile erection and a single ventral corpus spongiosum that surrounds the glans penis and extends distally to form the glans penis
- In general, the penile artery (which is a branch of the internal pudendal artery that, in turn, is a branch from the internal iliac artery) supplies the penis. It divides into three branches: dorsal artery, bulbar artery (supplies the corpus spongiosum), and cavernosal artery (the main blood supply to the erectile tissue).
- During an erection, smooth muscle relaxation of the cavernosal arterioles results in high-volume inflow to the sinusoids, resulting in compression of the exiting venules. This leads to significant volume expansion of the corpora cavernosa.
- During the flaccid resting state, the sympathetic nervous system is predominantly in control. Penile tumescence and erection are driven by the parasympathetic nervous system through the generation of nitric oxide (NO).
- Smooth muscle relaxation occurs via usage of the phosphodiesterase type 5 (PDE5A) pathway, which generates cyclic guanosine monophosphate (cGMP).
Etiology and Pathophysiology
- In ischemic priapism, decreased venous outflow results in increased intracavernosal pressure. This leads to erection, decreased arterial inflow, blood stasis, local hypoxia, and acidosis (a compartment syndrome). Penile tissue necrosis and fibrosis may occur if priapism persists beyond 24 hours. The exact mechanism is unknown and may involve trapping of erythrocytes in the veins, draining the erectile bodies.
- In nonischemic priapism, increased arterial flow without decreased venous outflow results in a sustained, nonpainful, partially rigid erection.
- Aberrations in the PDE5A pathway have been proven in mice to be one mechanism of priapism.
- Causes: ischemic priapism
- Idiopathic, estimated to about 50% (1)
- Intracavernosal injections of vasoactive drugs for erectile dysfunction
- Oral agents for erectile dysfunction
- Pelvic vascular thrombosis
- Prolonged sexual activity
- Leukemia and other malignancies that can infiltrate the corpora
- SCD and trait
- Other blood dyscrasias (G6PD deficiency, thalassemia, thrombophilia)
- Pelvic hematoma or neoplasia (penis, urethra, bladder, prostate, kidney, rectal)
- Cerebrospinal tumors
- Fabry disease
- Tertiary syphilis
- Total parenteral nutrition, especially 20% lipid infusion (results in hyperviscosity)
- Bladder calculus
- UTIs, especially prostatitis, urethritis, cystitis
- Several drugs suspected as causing priapism (i.e., chlorpromazine, prazosin, cocaine [can be directly injected into penis], trazodone, and some corticosteroids), anticoagulants (heparin and warfarin), phosphodiesterase inhibitors (sildenafil, others), immunosuppressants (tacrolimus), antidepressants, methylphenidate, and antihypertensives (hydralazine, propranolol, guanethidine). Some case reports on antipsychotics (quetiapine, risperidone, aripiprazole).
- Intracavernous fat emulsion
- Hyperosmolar IV contrast
- Spinal cord injury
- General or spinal anesthesia
- Heavy alcohol intake
- Causes: nonischemic priapism
- The most common cause is penile or perineal trauma resulting in a fistula between the cavernous artery and the corpus cavernosum.
- Acute spinal cord injury
- Rarely, iatrogenic causes for the management of ischemic priapism can result in nonischemic priapism.
- Certain urologic surgeries have also resulted in nonischemic priapism.
- Avoid dehydration (SCD cases).
- Avoid excessive sexual stimulation.
- Avoid causative drugs (see “Etiology and Pathophysiology”) when possible.
- Avoid physical activity with a high risk of blunt trauma to the genital area.
Commonly Associated Conditions
- SCD (42.9%) or sickle cell trait (2.5%)
- Drug abuse (7.9%)
- G6PD deficiency