Erectile Dysfunction 

Sexual health and function are important determinants of quality of life.^[1] Disorders such as erectile dysfunction (ED) and female sexual dysfunction are becoming increasingly more important as a result of the aging US population and newer therapies. Because this subject is discussed widely in the media, men and women of all ages are seeking guidance in an effort to improve their relationships and experience satisfying sexual lives.

The first step in treating the patient with ED is to take a thorough sexual, medical, and psychosocial history. Questionnaires are available to assist clinicians in obtaining important patient data. (See Clinical Presentation and History Taking in the Erectile Dysfunction Patient)

Successful treatment of sexual dysfunction has been demonstrated to improve sexual intimacy and satisfaction, improve sexual aspects of quality of life, improve overall quality of life, and relieve symptoms of depression. (See Treatment.)

The availability of 3 phosphodiesterase-5 (PDE-5) inhibitors (ie, sildenafil [Viagra], vardenafil [Levitra], and tadalafil [Cialis]) has permanently altered the medical management of ED. In addition, direct-to-consumer marketing of these agents over the last 15 years has increased the general public's awareness of ED as a medical condition with underlying causes and effective treatments.

Unfortunately, some patients have gleaned a simplistic understanding of the role of PDE-5 inhibitors in ED management. Such patients may not expect or be willing to undergo a long evaluation and testing process to obtain a better understanding of their sexual problem, and they are less likely to involve their partner in a discussion of their sexual relationship with the physician. They may wish to obtain medications by a phone call to their doctor or even over the Internet with minimal or no physician contact at all.

The physician's role in such cases may need to include educating patients about realistic sexual expectations (see Patient Education). These efforts can help prevent the misuse or overuse of these remarkable medications.

Although this article focuses primarily on the male with ED, one must remember that the sexual partner plays an integral role. If successful and effective management is to be achieved, the evaluation and discussion of any intervention should include both partners.

An understanding of penile anatomy is fundamental to management of erectile dysfunction (ED).^[2] The common penile artery, which derives from the internal pudendal artery, branches into the dorsal, bulbourethral, and cavernous arteries. See the image below.

The dorsal artery provides for engorgement of the glans during erection, while the bulbourethral artery supplies the bulb and corpus spongiosum. The cavernous artery effects tumescence of the corpus cavernosum, and thus is principally responsible for erection. The cavernous artery gives off many helicine arteries, which supply the trabecular erectile tissue and the sinusoids. These helicine arteries are contracted and tortuous in the flaccid state and become dilated and straight during erection.^[3]

Venous drainage of corpora originates in tiny venules that lead from the peripheral sinusoids immediately beneath the tunica albuginea. These venules travel in the trabeculae between the tunica and the peripheral sinusoids to form the subtunical venous plexus before exiting as the emissary veins.^[3] See the image below.

Sexual behavior involves the participation of autonomic and somatic nerves and the integration of numerous spinal and supraspinal sites in the central nervous system (CNS). The penile portion of the process that leads to erections represents only a single component.

The hypothalamic and limbic pathways play an important role in the integration and control of reproductive and sexual functions. The medial preoptic center, paraventricular nucleus, and anterior hypothalamic regions modulate erections and coordinate autonomic events associated with sexual responses.

Afferent information is assessed in the forebrain and relayed to the hypothalamus. The efferent pathways from the hypothalamus enter the medial forebrain bundle and project caudally near the lateral part of the substantia nigra into the midbrain tegmental region.

Several pathways have been described to explain how information travels from the hypothalamus to the sacral autonomic centers. One pathway travels from the dorsomedial hypothalamus through the dorsal and central gray matter, descends to the locus ceruleus, and projects ventrally in the mesencephalic reticular formation. Input from the brain is conveyed through the dorsal spinal columns to the thoracolumbar and sacral autonomic nuclei.

The primary nerve fibers to the penis are from the dorsal nerve of the penis, a branch of the pudendal nerve. The cavernosal nerves are a part of the autonomic nervous system and incorporate both sympathetic and parasympathetic fibers. They travel posterolaterally along the prostate and enter the corpora cavernosa and corpus spongiosum to regulate blood flow during erection and detumescence. The dorsal somatic nerves are also branches of the pudendal nerves. They are primarily responsible for penile sensation.^[4]

Penile erections involve an integration of complex physiologic processes involving the CNS, peripheral nervous system, and hormonal and vascular systems. Any abnormality involving these systems, whether from medication or disease, has a significant impact on the ability to develop and sustain an erection, ejaculate, and experience orgasm.

See Physiology of Erectile Dysfunction for more information on this topic.

ED usually has a multifactorial etiology. 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. Although most ED was once attributed to psychological factors, pure psychogenic ED is in fact uncommon. However, many men with organic etiologies may also have an associated psychogenic component.

Given the multiplicity of possible etiological factors, it may be difficult to determine how much any given factor is contributing to the problem. A thorough evaluation is necessary to correctly identify the specific etiology in any given individual.

ED is often associated with other vascular diseases and conditions such as diabetes,^{[5, 6, 7]} hypertension,^[8] and coronary artery disease. Other conditions associated with ED include neurologic disorders, endocrinopathies, benign prostatic hyperplasia,^[9] and depression.^{[10, 11, 12, 13]} In fact, 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 psychological mood and behavior.

Conditions associated with reduced nerve and endothelium function, such as aging, hypertension, smoking, hypercholesterolemia, and diabetes, alter the balance between contraction and relaxation factors. These conditions cause circulatory and structural changes in penile tissues, resulting in arterial insufficiency and defective smooth muscle relaxation. In some patients, sexual dysfunction may be the presenting symptom of these disorders.

A number of diseases, conditions, and medications have been associated with ED. (See Table 1 below.)

Table 1. Diseases and conditions associated with ED (Open Table in a new window)

Vascular diseases

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 result from radiation therapy to the pelvis and prostate in the treatment of prostate cancer.^[14] 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. Data indicate that 50% of men undergoing radiation therapy lose erectile function within 5 years after completing therapy. Fortunately, some tend to respond to one of the phosphodiesterase-5 (PDE-5) inhibitors.

Trauma

Trauma to the pelvic blood vessels or nerves can also lead result in ED. Bicycle riding for long periods has been implicated as an etiologic factor, as direct compression of the perineum by the bicycle seat may cause vascular and nerve injury (in contrast, bicycling for less than 3 hours per week may be somewhat protective against ED).^[15] Some of the newer bicycle seats have been designed to diminish pressure on the perineum.^{[15, 16]}

Diabetes mellitus

Diabetes is a well-recognized risk factor, with approximately 50% of diabetic men 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.

Abnormal cholesterol levels

The Massachusetts Male Aging Study (MMAS) 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 had a preponderance of older men.^[17]

Respiratory diseases

Men with sleep disorders commonly experience ED.^[18] Heruti et al recommended that in adult male patients, ED should be considered when a sleep disorder—especially sleep apnea syndrome—is suspected, and vice versa.^[19]

Endocrine disorders

Hypogonadism that results in low testosterone levels adversely affects libido and erectile function. Hypothyroidism is a very rare cause of ED.

Penile conditions

Peyronie disease may result in fibrosis and curvature of the penis. Men with severe Peyronie disease may have enough scar tissue in the corpora to impede blood flow.

Mental health disorders

Mental health disorders, particularly depression, are likely to affect sexual performance. The MMAS data indicate an odds ratio of 1.82 for men with depression. Other associated factors, both cognitive and behavioral, may contribute. In addition, ED alone can induce depression.

Cosgrove et al reported a higher rate of sexual dysfunction in veterans with posttraumatic stress syndrome than in those veterans who did not develop this problem.^[20] The domains on the International Index of Erectile Function (IIEF) questionnaire that demonstrated the most change included overall sexual satisfaction and erectile function.^{[21, 22]} Men with posttraumatic stress syndrome should be evaluated and treated if they have sexual dysfunction.

Prostate surgery

Prostate 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.

The community-based Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) study assessed whether an individual man’s sexual outcomes after most common treatments for early stage prostate cancer can be accurately predicted based on baseline characteristics and treatment plans. The researchers found that 2 years after treatment, 177 of 511 men (35%) who underwent prostatectomy reported the ability to attain functional erections suitable for intercourse; this corresponding figure was 37% of men who had received external radiotherapy as their primary therapy and 43% of men who had received brachytherapy as primary treatment. Pretreatment sexual health-related quality of life score, age, serum PSA level, race/ethnicity, body mass index, and intended treatment details were associated with functional erections 2 years after treatment.^[23]

Following surgery, one of the oral PDE-5 inhibitors (eg, sildenafil, vardenafil, tadalafil) is frequently used to assist in the recovery of erectile function. These agents have been shown to be effective in this setting.^{[24, 25]}

Medications

ED is an adverse effect of many commonly prescribed medications. For example, some psychotropic drugs and antihypertensive agents are associated with ED.

Inactivity

A sedentary lifestyle is a contributing factor to ED.^[26] Exercise has a beneficial effect on the cardiovascular system, and some data from the MMAS indicate that men who exercise regularly have a lower risk of ED.^[17]

Smoking

Cigarette smoking has been shown to be an independent risk factor. In studies evaluating more than 6000 men, the risk of developing ED increased by a factor of 1.5.

Sexual dysfunction is highly prevalent in men and women. In the MMAS, a community-based survey of men aged 40-70 years, 52% of the respondents reported some degree of erectile difficulty. Complete ED, defined as (1) the total inability to obtain or maintain an erection during sexual stimulation and (2) the absence of nocturnal erections, occurred in 10% of the respondents. Lesser degrees of mild and moderate ED occurred in 17% and 25% of responders, respectively.^[17]

Although the rate of mild ED in the MMAS remained constant (17%) in men aged 40-70 years, the number of men reporting moderate ED doubled (17-34%) and the number of men reporting complete ED tripled (5-15%). Extrapolating the MMAS data to the American population, an estimated 18-30 million men are affected by ED.^[27]

In the National Health and Social Life Survey (NHSLS), a nationally representative probability sample of men and women aged 18-59 years, 10.4% of men reported being unable to achieve or maintain an erection during the past year.^[28] This has a striking correlation to the proportion of men in the MMAS who reported complete ED.

All studies demonstrate a strong association with age, even when data are adjusted for the confounding effects of other risk factors. The independent association with aging suggests that vascular changes in the arteries and sinusoids of the corpora cavernosae, similar to those found elsewhere in the body, are contributing factors. Other risk factors associated with aging include depression, sleep apnea, and low levels of high-density lipoproteins.

Long-term predictions based on an aging population and an increase in risk factors (eg, hypertension, diabetes, vascular disease, pelvic and prostate surgery, benign prostatic hyperplasia, lower urinary tract symptoms) suggest a large increase in the number of men with ED. In addition, the prevalence of ED is underestimated because physicians frequently do not question their patients about this disorder.

Studies conducted around the world report similar risk factors and similar prevalence rates for ED.^{[29, 30]}

Other male sexual dysfunctions, such as premature ejaculation and hypoactive sexual desire, are also highly prevalent. The NHSLS found that 28.5% of men aged 18-59 years reported premature ejaculation and 15.8% lacked sexual interest during the past year. An additional 17% reported anxiety about sexual performance, and 8.1% had a lack of pleasure in sex.^[28]

In a prospective population-based study of 1,709 men aged 40-70 years, Araujo et al found that ED is significantly associated with increased all-cause mortality.^[31] The increase primarily resulted from cardiovascular mortality.

In a prospective study from the Prostate Cancer Prevention Trial database, Thompson et al reported that men presenting with ED had a significantly higher chance of developing a cardiovascular event over a 7-year followup period. The hazard ratio was 1.45, which is in the range of risk associated with current smoking or a family history of myocardial infarction.^[32]

A discussion of the laboratory results should be conducted with the patient, and if possible with his sexual partner as well. This educational process allows a review of the basic aspects of the anatomy and physiology of the sexual response. The possible etiology and associated risk factors, such as smoking and the use of various medications, can be reviewed. Treatment options and their benefits and risks should be discussed. This type of dialogue allows the patient and physician to develop a strategy that is most beneficial.

Patients with both ED and cardiovascular disease who receive treatment with an oral phosphodiesterase type 5 inhibitor require education in what to do if anginal episodes develop while the drug is in their system. This includes the importance of alerting emergency care providers to the presence of the drug, so that nitrate treatment is avoided.

Patients receiving penile prostheses are instructed in the operation of the prosthesis prior to surgery and again in the postoperative period. The prosthesis is not usually activated until approximately 6 weeks after surgery. This is to allow the edema and pain to subside. The prosthesis is checked in the office before the patient begins to use it.

For patient education information, see the following:

• Erectile Dysfunction Center
• Cancer and Tumors Center
• Impotence/Erectile Dysfunction
• Erectile Dysfunction FAQs
• Nonsurgical Treatment of Erectile Dysfunction
• Understanding Erectile Dysfunction Medications
• Causes of Erectile Dysfunction
• Diagnosing Erectile Dysfunction
• Surgical Treatment of Erectile Dysfunction
• Bladder Cancer