Priapism
ARTHUR L. BURNETT II
NATE READAL
Priapism refers to an erectile disorder in which an erection persists uncontrollably without sexual purpose. The general timeframe is any erection persisting beyond 4 hours. It is a medical emergency that requires prompt diagnosis and immediate treatment to prevent long-term sequelae, and a urologist should be involved early in the care of priapism patients. The disorder is a result of disturbances in the mechanisms governing erectile physiology as it relates to regulatory control of penile detumescence and initiation and maintenance of penile flaccidity. Priapism represents one of the greatest challenges in therapeutic management of erectile disorders, and although relatively rare, knowledge of proper management is required from urologists, emergency room personnel, and hematologists.
During an episode of ischemic priapism, blood fails to drain from the corporal sinusoids of the penis resulting in a prolonged, painful erection. Pain with priapism is believed to be a consequence of tissue ischemia and increased pressure within the corporal bodies that results from failure of blood egress. When prolonged, ischemic priapism leads to erectile dysfunction (ED) and prompt recognition, and diagnosis and management are necessary to minimize this risk. However, all patients should be aware that permanent ED is a possibility following a priapic episode, particularly if the duration of priapism is prolonged. Global penile fibrosis and impaired erectile mechanisms are the end result of untreated ischemic priapism and the overall rate of ED can be as high as 59% (1,2,3).
Priapism can be classified into two types, ischemic (or low flow, venous) priapism and nonischemic (or high flow, arterial) priapism. Ischemic priapism is the more common form, and greater than 95% of men who present with priapism will have the ischemic type (4). It is typically a result of pharmacologic use/abuse, hematologic disorders, or neurogenic causes (Table 68.1) and results in a persistent, painful erection with no cavernosal blood flow. Cavernosal blood gas is acidotic, hypoxic, and hypercarbic, and the increased pressure within the closed corporal system gives rise to a compartment syndrome that compromises cavernosal tissue oxygenation. After 24 hours of ischemic priapism, there is evidence of irreversible smooth muscle cell necrosis, destruction of vascular endothelium, and exposure of the basement membrane with adherence of thrombocytes (5).
TABLE 68.1 CAUSES OF PRIAPISM | ||||||
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Stuttering or recurrent priapism is a variant of ischemic priapism in which patients have recurrent, undesired erections characterized by prolongation and pain but a duration typically less than 3 hours (5). It is commonly encountered in sickle cell patients and episodes typically occur upon awakening from sleep and can be self-limited. These episodes are marked by intervals of detumescence and may become longer in both duration and severity until a full episode of ischemic priapism (>4 hours) results in as many as 28% of patients (6). Each episode confers a risk of fibrosis to the corpora cavernosa if not promptly recognized and treated to restore normal corporal blood flow and oxygenation.
Nonischemic priapism is a nonsexual, persistent erection that typically follows trauma to the perineum or genitalia resulting in unregulated cavernosal arterial inflow to the
corporal bodies (1). The corpora are typically semirigid and nonpainful as oxygenated, arterial inflow is constant. Unlike ischemic priapism, corporal blood gas is neither hypoxic, hypercarbic, nor acidotic, and this type of priapism is not an emergency as the corporal tissue remains well oxygenated and painful symptoms are rare.
corporal bodies (1). The corpora are typically semirigid and nonpainful as oxygenated, arterial inflow is constant. Unlike ischemic priapism, corporal blood gas is neither hypoxic, hypercarbic, nor acidotic, and this type of priapism is not an emergency as the corporal tissue remains well oxygenated and painful symptoms are rare.
CLINICAL CHARACTERISTICS
Incidence/Prevalence
Epidemiologic data on the incidence of priapism are not abundant as such data depend on accurate recording of cases at clinics and hospitals throughout the world which does not regularly occur. Studies evaluating the incidence of priapism are typically performed in a homogenous population in which various risk factors may be present or absent, thus limiting the generalization of the results. Several such studies, however, do give some insight into the incidence of priapism in select populations. Kulmala and colleagues (7) using primary care databases determined the incidence of priapism in Finland from 1976 to 1990 to be 0.34 to 0.52 cases per 100,000 male patients per year. The incidence rates in the Netherlands and Australia were slightly higher at rates of 1.5 per 100,000 person-years and 0.84 per 100,000 person-years, respectively (2,8). New data taken from the National Emergency Department Sample database, which collects emergency department visit information from select states in the United States, has allowed a better understanding of the contemporary incidence of priapism episodes in the United States which was estimated to be 0.73 per 100,000 men per year from 2006 to 2009 (9). The incidence of hospitalization for priapism was 0.01 per 100,000 men per year, and although hospitalization for priapism is relatively rare, such an event is economically significant with an average cost of $41,909 to the health care system. In contrast, an emergency room visit for priapism has an average cost of $1,778 (9,10).
In certain select populations, however, the occurrence of priapism is known to be significantly higher. In Jamaica, where 1 in 300 children are born with sickle cell disease, the prevalence of men who have had an episode of priapism in the population is 42% and the risk of men with sickle cell disease developing an episode of priapism by the age of 20 is 89% (11). It is known that men with sickle cell disease have a lifetime risk of developing an episode of ischemic priapism of 29% to 42%, and with 20 to 25 million men worldwide who are homozygous for sickle cell disease, this represents a significant population at risk for priapism episodes (3).
Risk Factors
Priapism is associated with diverse disease states. Etiologic categories for ischemic priapism include idiopathic, which is the most common cause, neurologic conditions (multiple sclerosis, spinal cord tumor, acute spinal cord injury), hematologic dyscrasias (sickle cell disease, thalassemias, leukemia, multiple myeloma), malignancies (metastatic or local), vasoactive erectile medication therapy (prostaglandin E1, papaverine), prescribed and recreational drug exposure (testosterone replacement, psychotropic and antidepressant medications, alcohol and illicit drugs), toxin-induced (scorpion sting or Phoneutria nigriventer spider bite) and rarely anxiety disorders, metabolic disease, or exposure to anesthesia (12,13).
Nonischemic priapism typically results from trauma to the perineum or genitalia such as a straddle injury, coital trauma, or blunt trauma such as a kick or strike. However, arteriocavernous fistulas can also result from needle lacerations occurring during penile injection therapy, direct injury during surgical procedures in the penis or perineum, or penile revascularization procedures.
PATHOPHYSIOLOGY
Ischemic priapism consists of an imbalance of vasoconstrictive and vasorelaxatory mechanisms that predispose the penis to prolonged tumescence and the development of hypoxia and acidosis. A new understanding of the molecular mechanisms leading to priapism has recently been advanced through the use of both transgenic and sickle cell disease rodent models that demonstrate multiple perturbations in these pathways contributing to the development of priapism. In endothelial nitric oxide synthase knockout and transgenic sickle cell mice, exaggerated erectile responses to cavernous nerve stimulation are observed consistent with priapism (14). The mechanism of priapism in these animals is believed to be due to chronically impaired basal endothelial nitric oxide bioavailability due to a defect in the nitric oxide signaling pathway. This results in downregulation of nitric oxide synthase activity and ultimately decreased cyclic guanosine monophosphate (cGMP) production with compensatory downregulation of phosphodiesterase type 5 (PDE5) expression in the basal state. When an erectogenic stimulus is experienced, cGMP accumulates in corporal smooth muscle causing uncontrolled dilation. With little PDE5 present to degrade the cGMP, complete, prolonged corporal body dilation ensues and priapism results (15). Adenosine overproduction has also been implicated in the development of priapism (16). Adenosine acts through the stimulation of adenylyl cyclase and synthesis of cyclic adenosine monophosphate, which activates protein kinase A and enhances smooth muscle relaxation. Increased adenosine production was present in the penis of sickle cell mice and mice that lacked adenosine deaminase, the enzyme responsible for degrading adenosine to inosine. The addition of adenosine deaminase to degrade adenosine resulted in smooth muscle contraction and resolution of priapism episodes in these animals (16).
Perturbations in the vasoconstrictive pathways that maintain penile flaccidity have also been demonstrated in sickle cell mouse penis (17). Sickle cell mouse penis demonstrates decreased Rho A activity leading to decreased ROCK2 expression and decreased total ROCK activity, all contributing to decreased basal vasoconstriction in the penis. The limited contractile ability of the corporal tissue leads to susceptibility of the tissue to excessive relaxation leading to priapism. Thus, priapism results from alterations in the vasoconstrictive and vasorelaxatory pathways of the penis that drives the organ into a state of smooth muscle hyperrelaxation and erection with little contractile reserve to counteract the process and return the penis to a flaccid state.
Ischemic priapism can also result from malignant infiltration of the penis by local or metastatic cancer, and priapism may be the presenting feature of metastatic disease to the penis
in 27% of cases (18). The pathophysiology of malignant priapism can be secondary to either direct tumor infiltration of the corpora cavernosa or invasion of penile venous structures that inhibits drainage, promotes venous stasis, and leads to thrombosis within the penis (18).
in 27% of cases (18). The pathophysiology of malignant priapism can be secondary to either direct tumor infiltration of the corpora cavernosa or invasion of penile venous structures that inhibits drainage, promotes venous stasis, and leads to thrombosis within the penis (18).
DIAGNOSIS
Diagnosis and classification of priapism are based on clinical evaluation, including laboratory tests and corporal blood gas measurement via aspirated blood directly from the corpora cavernosa (12). A diagnostic and therapeutic algorithm is provided in Figure 68.1. Initial evaluation should focus on differentiation between ischemic and nonischemic priapism because this will guide both the type and urgency of further management. Patients should have a detailed history and physical examination with an emphasis on possible causative factors (see Table 68.1). Important historical factors are duration of current event, history of priapism, and baseline erectile function. A detailed medical and social history to evaluate for hematologic or neurologic conditions and review of both prescription and illicit drug use must be performed. Prolonged duration with progressively worsening penile pain favors ischemic priapism, whereas nonpainful, partial erection with preceding trauma, instrumentation, or surgery favors nonischemic priapism. Physical examination should be directed to the penis and perineum to evaluate degree of pain and rigidity while inspecting for any neurologic defect, pelvic or penile masses, or evidence of trauma. Laboratory evaluation includes a complete blood count and reticulocyte count to evaluate for anemia, infection, or other hematologic abnormalities. A sickle cell anemia screen can be used when appropriate. A urinalysis and urine toxicology screen for recent illicit, narcotic, or psychoactive drug use should be ordered.
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