DEFINITION

Erectile dysfunction is the inability to develop and maintain an erection for satisfactory sexual intercourse or activity in the absence of an ejaculatory disorder such as premature ejaculation. Erectile dysfunction is the preferred term rather than the more commonly used term, impotence. There are no universally agreed on criteria for how consistent the problem has to be and for what duration it needs to be present to fulfill the definition. A period of persistence for longer than 3 months has been suggested as a reasonable clinical guideline.

PREVALENCE

Several studies have looked at the prevalence of erectile dysfunction. The Massachusetts Male Aging Study, conducted from 1987 to 1989 in areas around Boston, was a cross-sectional random sample community-based survey of 1290 men ages 40 to 70 years.¹ Erectile dysfunction was self-reported and the condition was classified as mild, moderate, or complete. The combined prevalence of minimal, moderate, and complete erectile dysfunction was 52%. The study demonstrated that erectile dysfunction is increasingly prevalent with age. At age 40, there is an approximately 40% prevalence rate, increasing to almost 70% in men at age 70. The prevalence of moderate erectile dysfunction increases from 17% to approximately 34%; the prevalence of complete erectile dysfunction increases from 5% to 15% as age increases from 40 to 70 years.

Although age was the variable most strongly associated with erectile dysfunction, following adjustment for age, a higher probability was noted with heart disease, hypertension, diabetes, and associated medications. Cigarette smoking in this study did not correlate with a greater probability of complete erectile dysfunction. However, when it was associated with heart disease and hypertension, a higher probability of erectile dysfunction was noted. The study concluded that erectile dysfunction is a major health concern in light of its high prevalence.

Incidence estimates have been published using data compiled from the Massachusetts Male Aging Study.² Incidence data are necessary to assess risk and plan treatment and prevention strategies. The Massachusetts study data have suggested there will be approximately 17,781 new cases of erectile dysfunction in Massachusetts and 617,715 in the United States annually. The national incidence estimate might underestimate the true incidence, because Massachusetts is largely white, so likely the data are underestimated nationally for African Americans, Latin Americans, and other groups.

A larger national study, the National Health and Social Life Survey, looked at sexual function in men and women.³ This study surveyed 1410 men ages 18 to 59 years, and it also documented an increase in erectile dysfunction with age. Additionally, the study found a decrease in sexual desire with increasing age. The oldest cohort of men (ages 50-59 years) was more than three times as likely to experience erection problems and to report low sexual desire in comparison with men ages 18 to 29 years. In this study, there was a higher prevalence of sexual dysfunction in men who had never married or were divorced. Experience of sexual dysfunction was more likely among men in poor physical and emotional health. It was also concluded that sexual dysfunction is an important public health concern and added that emotional issues are likely to contribute to the experience of these problems.

PATHOPHYSIOLOGY

The development of an erection is a complex event involving integration of psychological, neurologic, endocrine, vascular, and local anatomic systems. Positron emission tomography (PET) scanning studies⁴ have suggested that sexual arousal is activated in higher cortical centers, which then stimulate the medial preoptic and paraventricular nuclei of the hypothalamus. These signals ultimately descend through a complex neural network involving the parasympathetic nervous system and eventually activate parasympathetic nerves in the sacral area (S2 to S4).

The neurovascular events that ultimately occur result in the inhibition of adrenergic tone and release of the nonadrenergic, noncholinergic (NANC) neurotransmitter nitric oxide. Nitric oxide is believed to be released from NANC nerves and endothelial cells. Nitric oxide stimulates the guanylate cyclase enzyme system in penile smooth muscle. This results in increased levels of cyclic guanosine monophosphate (GMP) and ultimately in smooth muscle relaxation, enhancement of arterial inflow, and veno-occlusion, producing adequate firmness for sexual activity.

Abnormalities in any of these systems can produce erectile dysfunction. For example, cerebral vascular accidents, multiple sclerosis, Parkinson’s disease, and spinal cord injury can result in neurogenic erectile dysfunction. More commonly, vascular disease and diabetes can produce neurovascular abnormalities resulting in erectile dysfunction. Surgery for cancers of the prostate, bladder, and colon can also produce neurovascular abnormalities resulting in erectile dysfunction. Diseases such as Peyronie’s disease, in which patches or strands of dense tissue surround the cavernous body of the penis, and traumatic perineal and penile injuries can also interfere with neurovascular and anatomic structures, producing erectile dysfunction.

Hormone deficiency or hypogonadism, whether primary or secondary, can result in erectile dysfunction. Hormone deficiency, however, is less often the cause of erectile dysfunction than is diabetes or vascular disease. How often erectile dysfunction is caused by hormone deficiency remains somewhat controversial, but estimates of approximately 3% to 5% of cases are probably reasonable. Medications and recreational drugs can also produce erectile dysfunction by various poorly understood mechanisms.

SIGNS AND SYMPTOMS

Although erectile dysfunction is a common problem, many patients are reluctant to discuss it. Certainly, some patients who present with issues relating to depression or anxiety disorders actually have a significant problem with erectile dysfunction. Additionally, patients who are poorly compliant with medication prescribed for hypertension may be experiencing significant erectile dysfunction. The best way to elicit whether the problem is present is to ask questions about sexual function as a routine part of the examination.

Some health questionnaires help screen for and evaluate erectile dysfunction⁵ and may help in the primary care setting. It is important, however, to recognize that abbreviated questionnaires might not evaluate specific areas of the sexual cycle, such as sexual desire, ejaculation, and orgasm. Nonetheless, they can be useful in helping patients discuss the problem and in signaling the need for an evaluation.

DIAGNOSIS

If it is determined that erectile dysfunction is a problem, a detailed sexual and medical history should be elicited and a physical examination should be done to evaluate the problem. In particular, it is important to evaluate the erectile dysfunction and make sure that the problem is not premature ejaculation, which is also a common sexual dysfunction.⁶

A number of specific questions relating to sexual function help evaluate the complaint of erectile dysfunction. Questions should focus on the following:

Once questions related to the specific erectile complaint have been reviewed, additional questions relating to medical and psychosocial factors need to be evaluated. In particular, these include the following: symptoms suggesting the presence of diabetes, peripheral vascular disease, neurologic disease, or chronic liver or kidney disease; a complete list of medications and recreational drugs, including alcohol, and questions about cigarette smoking; previous history of surgery or radiation therapy, particularly procedures related to genitourinary or gastrointestinal malignancy; a history of pelvic genital, perineal, or spinal cord trauma; and the quality of the marital or partner relationship and expectations of both patient and partner.

Following a review of the medical history, the salient features of the physical examination should include the following:

Once a complete sexual and medical history has been completed, appropriate laboratory studies can be considered. In the initial evaluation of erectile dysfunction, sophisticated laboratory testing is rarely necessary. Laboratory studies should include hormonal evaluation to exclude a diagnosis of hypogonadism (testosterone and prolactin levels) and testing to screen for diabetes if the patient is not known to be diabetic (hemoglobin A_1c or glucose tolerance testing). Most patients usually have had a general survey, but this is certainly appropriate if it has not been done to assess for kidney or liver disease. A lipid panel is also appropriate as a screen for risk factors.

In most cases, a tentative diagnosis can be established with a complete sexual and medical history, physical examination, and limited laboratory testing. In many cases, the diagnosis still remains somewhat ambiguous. However, with the availability of oral medication for treatment of erectile dysfunction that is safe and has minimal or tolerable side effects, additional diagnostic testing is probably unnecessary or can be delayed until a therapeutic trial of oral medication has proved ineffective.