What causes priapism?

Causes of Priapism

Priapism is primarily caused by veno-occlusive mechanisms that prevent blood outflow from the corpora cavernosa, resulting in prolonged, painful erections lasting more than 4 hours without sexual stimulation. 1

Types of Priapism and Their Distinct Causes

Ischemic (Low-Flow) Priapism (95% of cases)

• Pharmacological causes:

  • Intracavernosal injection therapies for erectile dysfunction 1, 2
  • Alpha-adrenergic antagonists (e.g., prazosin, especially with rapid titration) 3
  • Phosphodiesterase-5 inhibitors (sildenafil, tadalafil) 4, 5
  • Antipsychotics and antidepressants
  • Recreational drugs (cocaine, alcohol, marijuana)

• Hematologic disorders:

  • Sickle cell disease (most common hematologic cause) 1, 6
  • Leukemia
  • Multiple myeloma
  • Thalassemia
  • Polycythemia

• Neurologic disorders:

  • Spinal cord injury
  • Stroke
  • Brain tumors

• Metabolic conditions:

  • Amyloidosis
  • Fabry disease
  • Diabetes

• Idiopathic causes (30-50% of cases)

Non-Ischemic (High-Flow) Priapism (5% of cases)

• Trauma:
  • Perineal straddle injury (most common cause) 1
  • Penile trauma
  • Iatrogenic injury during penile or pelvic surgery
  • Arterial-lacunar fistula formation 7

Stuttering (Recurrent Ischemic) Priapism

• Primary cause:
  • Sickle cell disease 1, 6
• Secondary causes:
  • Other hematologic disorders
  • Neurologic conditions
  • Medication side effects

Pathophysiology of Priapism

Ischemic Priapism

• Failure of detumescence mechanisms 1
• Veno-occlusion leading to:
  • Hypoxia (PO₂ <30 mmHg)
  • Hypercapnia (PCO₂ >60 mmHg)
  • Acidosis (pH <7.25) 1, 2
• Prolonged ischemia (>4 hours) causes:
  • Cavernous tissue damage
  • Smooth muscle apoptosis
  • Fibrosis and permanent erectile dysfunction 8

Non-Ischemic Priapism

• Unregulated arterial inflow to corpora cavernosa 1
• Normal blood gas values (not hypoxic or acidotic) 1
• Usually painless and not fully rigid 1

Risk Factors for Priapism

• Medications:

  • Alpha-blockers (especially with rapid dose escalation) 3
  • PDE-5 inhibitors in patients with anatomical deformation of the penis 4
  • Intracavernosal injection therapy for erectile dysfunction 2

• Medical conditions:

  • Sickle cell disease (most significant risk factor) 6
  • Malignancies (especially genitourinary) 1
  • Hypercoagulable states

• Anatomical factors:

  • Cavernosal fibrosis
  • Peyronie's disease
  • Penile angulation 4

Clinical Implications

• Ischemic priapism is a true urologic emergency requiring immediate treatment 1
• Risk of permanent erectile dysfunction increases significantly after:
  • 18 hours of ischemia
  • Near certainty after 36 hours 2
• Early recognition and intervention are critical to preserve erectile function 9
• Patients with sickle cell disease require special attention due to high recurrence risk 6

Prevention Strategies

• For patients with recurrent priapism:
  • Alpha-adrenergic agonists
  • Hormonal agents
  • PDE-5 inhibitors (paradoxically can help prevent stuttering priapism)
  • Self-injection of sympathomimetics at home for early intervention 2

Understanding the specific cause of priapism is essential for appropriate management and prevention of recurrence, with time being the most critical factor in preserving erectile function.