erectile dysfunction
Summary
Erectile dysfunction (ED) is the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance. It is commonly vascular in etiology (endothelial dysfunction), especially in older men, and is an important marker of underlying cardiovascular disease. First-line treatment is PDE5 inhibitors (e.g., sildenafil).
Detail
Erection physiology depends on parasympathetic (pelvic splanchnic nerves, S2-S4) stimulation causing release of nitric oxide (NO) from endothelium and nerve terminals in the corpus cavernosum. NO activates guanylate cyclase, increasing cGMP, which causes smooth muscle relaxation, arterial dilation, and venous outflow restriction, resulting in engorgement. Detumescence occurs via cGMP breakdown by phosphodiesterase-5 (PDE5) and sympathetic-mediated vasoconstriction.
Etiologies of ED are broadly categorized as: 1. Vascular/Endothelial (most common, especially >50 yrs): atherosclerosis, hypertension, diabetes mellitus, smoking, hyperlipidemia - shared risk factors with coronary artery disease. ED often precedes CAD diagnosis by 2-3 years, so it serves as a sentinel marker for systemic vascular disease. 2. Neurogenic: spinal cord injury, multiple sclerosis, diabetic autonomic neuropathy, post-prostatectomy nerve damage. 3. Hormonal: hypogonadism (low testosterone), hyperprolactinemia, hypothyroidism. 4. Psychogenic: performance anxiety, depression, relationship issues - often sudden onset, normal nocturnal erections. 5. Drug-induced: antihypertensives (thiazides, beta-blockers), SSRIs, antipsychotics, alcohol, finasteride. 6. Structural: Peyronie's disease, penile trauma.
Workup includes history (onset, psychogenic vs organic), testosterone level, lipid panel, glucose/HbA1c, and assessment of cardiovascular risk. Nocturnal penile tumescence testing can differentiate psychogenic (preserved) from organic (absent) causes.
Treatment: First-line is PDE5 inhibitors (sildenafil, tadalafil, vardenafil) which prevent cGMP breakdown, enhancing NO-mediated vasodilation. Contraindicated with nitrates due to risk of severe hypotension (synergistic cGMP accumulation). Second-line options include intracavernosal injections (alprostadil), vacuum erection devices, and vardenafil. Third-line is penile prosthesis implantation. Address underlying causes: optimize glycemic control, treat hypogonadism with testosterone replacement if indicated, adjust offending medications, and manage cardiovascular risk factors given the strong association with CAD.
High-yield board point: ED as a harbinger of cardiovascular disease - it should prompt cardiovascular risk stratification.
Sources
- First Aid for the USMLE Step 1
- UpToDate: Erectile Dysfunction
- Campbell-Walsh Urology
- Katzung's Basic and Clinical Pharmacology
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