Etiology
The etiology of priapism can broadly be categorized as ischemic (low-flow) and nonischemic (high-flow). The flow refers to arterial vascular blood streaming into the corpora cavernosa. The causes of ischemic priapism are numerous and include various hemoglobinopathies, such as sickle cell disease and thalassemia, as well as any hypercoagulable state.[7] Vasoactive medications, including erectile dysfunction medications such as phosphodiesterase (PDE) type 5 inhibitors and intracavernous injections, have been blamed for an increased incidence of this disorder and are thought to cause at least 25% of all cases.[8][9]
Antidepressants, such as trazodone; antipsychotics, especially those with alpha-1 adrenergic receptor blocking capability; and illicit drugs, including amphetamines and cocaine, may also cause priapism.[10][11][12][13] Trazodone is the single drug associated with the highest incidence of medication-induced priapism at about 16% of cases.[14][15] Alpha-1 adrenergic receptor blockage inhibits the ability of the sympathetic nervous system to cause detumescence.[10] Surprisingly, priapism following the use of PDE type 5 inhibitors, such as sildenafil, tadalafil, and vardenafil, is relatively rare. Antipsychotics and trazodone are more than twice as likely to cause priapism as PDE type 5 inhibitors.[16][17]
Less common causes include neoplastic processes, including leukemias, melanoma, prostate cancer, renal cancer, and especially bladder cancer; amyloidosis; dialysis; Fabry disease; fat embolisms; carbon monoxide poisoning; cauda equina syndrome; glucose-6-phosphate dehydrogenase deficiency; neurologic disorders; and infections that produce a hypercoagulable state.[18][19][20][21][22]
Recurrent ischemic causes of priapism share many of the same underlying etiologic factors as acute ischemic priapism, except for some defective regulatory mechanisms, which can result in abnormal signaling and intermittent, repeated episodes of the disorder.[23]
Malignancies of the male pelvis can cause priapism due to either direct tumor infiltration or blockage of venous outflow, which can be identified with magnetic resonance imaging (MRI). The reported incidence of such malignant priapism is as high as 3.5% of patients presenting with priapism.[24]
Rare medication-related causes of priapism include hydroxyzine, drotaverine (a papaverine analog), low-molecular-weight heparin, and coagulopathy generally associated with coronavirus.[25][26][27][28] Other rare causes of priapism include chronic myeloid leukemia, COVID-19, thalassemias, amyloidosis, scorpion stings, spider bites, spinal cord injuries, and electronic cigarette use.[2][29][30][31]
Nonischemic high-flow priapism is far less common than the ischemic variety and typically results from direct perineal trauma or injury.[32] Nonischemic priapism can also result from iatrogenic injury during surgical interventions, congenital arterial malformations, or cancer.[32] In some cases, no underlying cause or explanation can be found for the disorder.[33][34]
