The etiology of ED is usually multifactorial. Organic, physiologic, endocrine, and psychogenic factors are involved in the ability to obtain and maintain erections. In general, ED is divided into organic and psychogenic impotence, but most men with organic etiologies usually have an associated psychogenic component. Almost any disease may affect erectile function by altering the nervous, vascular, or hormonal systems. Various diseases may produce changes in the smooth muscle tissue of the corpora cavernosa or influence the patient's psychologic mood and behavior. Pure psychogenic ED is an uncommon disorder, although most ED was once attributed to psychological factors.
Diabetes is a well-recognized risk factor, with up to 50% of men with diabetes experiencing ED. The etiology of ED in diabetic men probably involves both vascular and neurogenic mechanisms. Evidence indicates that establishing good glycemic control can minimize this risk.
Cigarette smoking has been shown to be an independent risk factor. Studies have shown that the risk of developing ED increased by a factor of 2 in men who smoke.
Mental health disorders, particularly depression, are likely to affect sexual performance. Other associated factors, both cognitive and behavioral, may contribute. Also, ED alone can induce depression. The new oral agents have been shown to be effective for men who develop depression following prostatectomy.
Cosgrove et al have reported a higher rate of sexual dysfunction in veterans with posttraumatic stress syndrome than in those veterans who did not develop this problem. The domains on the IIEF questionnaire that demonstrated the most change included overall sexual satisfaction and erectile function. This study suggests that regardless of etiology, men with posttraumatic stress syndrome should be evaluated and treated if they have sexual dysfunction.
A sedentary lifestyle is also a contributing factor to ED. Exercise has a beneficial effect on the cardiovascular system, and some data from the MMAS study indicate that men who exercise regularly have a lower risk of ED. However, Goldstein et al reported an increased risk of ED in men who rode a bicycle for long periods. Therefore, the type of exercise may be important.
The MMAS study also showed an inverse correlation between ED risk and high-density lipoprotein cholesterol levels but no effect from elevated total cholesterol levels. Another study involving male subjects aged 45-54 years found a correlation with abnormal high-density lipoprotein cholesterol levels but also found a correlation with elevated total cholesterol levels. The MMAS study had a preponderance of older men.
Vascular diseases account for nearly half of all cases of ED in men older than 50 years. Vascular diseases include atherosclerosis, peripheral vascular disease, myocardial infarction, and arterial hypertension.
Vascular damage may accompany radiation therapy to the pelvis and prostate in the treatment of prostatic cancer. In this situation, both the blood vessels and the nerves to the penis may be affected. Radiation damage to the crura of the penis, which are quite susceptible to radiation damage, can induce ED. The radiation oncologist must take precautions to avoid treating this area. Data indicate that 50% of men undergoing radiation therapy lose erectile function within 5 years after completing therapy. Fortunately, some of these men tend to respond to one of the PDE-5 inhibitors.
Prostatic surgery for benign prostatic hyperplasia has been documented to be associated with ED in 10-20% of men. This is thought to be related to nerve damage from cautery. Newer procedures such as microwave, laser, or radiofrequency ablation have rarely been associated with ED.
Radical prostatectomy for the treatment of prostate cancer poses a significant risk of ED. A number of factors are associated with the chance of preserving erectile function. If both nerves that course on the lateral edges of the prostate can be saved, the chance of maintaining erectile function is reasonable. This depends on the age of the patient. Men younger than 60 years have a 75-80% chance of preserving potency, but men older than 70 years have only a 10-15% chance. Sural nerve grafts are used by some surgeons. Following surgery, one of the PDE-5 inhibitors, such as sildenafil, vardenafil, or tadalafil, is frequently used to assist in the recovery of erectile function.
Trauma to the pelvic blood vessels and nerves is another potential etiologic factor in the development of ED. Bicycle riding for long periods has been implicated as an etiologic factor by causing vascular and nerve injury. Some of the newer bicycle seats have been designed to diminish pressure on the perineum.
Diseases associated with ED are summarized as follows:
- Vascular diseases associated with erectile dysfunction
- Systemic diseases associated with erectile dysfunction
- Neurogenic diseases associated with erectile dysfunction
- Respiratory disease associated with erectile dysfunction
- Endocrine conditions associated with erectile dysfunction
- Penile conditions associated with erectile dysfunction
- Psychiatric conditions associated with erectile dysfunction
Nutritional states associated with erectile dysfunction
- Zinc deficiency
Hematologic diseases associated with erectile dysfunction
- Surgical procedures associated with erectile dysfunction
Procedures on the brain and spinal cord
Retroperitoneal or pelvic lymph node dissection
Aortoiliac or aortofemoral bypass
Abdominal perineal resection
Surgical removal of the prostate for cancer
Surgical treatment of the prostate for benign disease
Transurethral resection of the prostate
Cryosurgery of the prostate
Medications associated with erectile dysfunction: