What is erectile dysfunction (ED) and how common is it?

The National Institutes of Health (NIH) definition of erectile dysfunction (ED), previously called impotence, is the consistent inability to achieve and/or maintain an erection satisfactory for the completion of sexual performance. The definition is subjective, meaning that the individual (and/or his partner) is the person who decides that his erections are not satisfactory. This is in comparison to an objective definition, in which an observer or a test makes the decision that the erection is not satisfactory. The definition is not an all-or-nothing one, meaning that different men may experience different degrees of ED. The most severe form of ED would be the complete absence of erections—no nocturnal (nighttime) erections, morning erections, or erections noted with stimulation; milder forms may be associated with inadequate degree or duration of rigidity.

The Massachusetts Male Aging Study was probably the first study that brought to light how common ED is. This study demonstrated that 52% of men between the ages of 40 years and 70 years have some degree of ED (Figure 30). Of those individuals, 10% noted complete ED, 25% noted moderate ED, and most noted mild ED.

In the United States, approximately 50 million men suffer from ED. The prevalence (number of cases of a

Figure 30. Prevalence of erectile dysfunction.

Adapted with permission from Feldman HA, Goldsteain I, Hatzichristou DG, Krane RJ, and McKinley JB: Impotence and its medical and psychological correlates: Results of the Massachusetts Male Aging Study. JUro/1994;151:54—61.

disease that are present at a given point in time) of ED is age dependent, with the rate of complete ED increasing from 5% among men 40 years old to 15% among those 70 years old. As our population continues to grow and age, we can only expect this number to increase. The worldwide prevalence of ED was 152 million in 1995 and is expected to increase to 322 million in 2025. Much of this increase will occur in the developing world and reflects the aging of the world's population.

The incidence (i.e., the number of new cases occurring during a specific period of time) of ED is higher in men with certain diseases, such as diabetes mellitus, hypertension, cardiovascular disease, spinal cord injury, and hypercholesterolemia (high cholesterol levels).

ED is a form of sexual dysfunction. The term sexual dysfunction applies to a variety of problems with sex, so the two terms are not really interchangeable (see Question 67). It is important that you determine early in your visit with your doctor whether your problem is ED and not another type of sexual dysfunction.

ED is not a disease in and of itself; rather, it is a manifestation of an underlying medical condition. It is important to evaluate men with ED to identify the underlying disease process(es) that is causing this problem because it may be a symptom (i.e., subjective evidence) of a condition that could cause the individual further harm. In addition, by treating the underlying disease processes, one may hopefully prevent further progression of the ED.

What causes ED?

Many medical conditions and medications (Table 16) can cause ED. Smoking, alcohol abuse, drug abuse, stress, and depression can also cause ED. Considering erectile function as a neurovascular event, we can divide the causes of ED into those that affect the brain and nerves (neurologic) and those that affect the arteries and veins (vascular).

Neurologic Conditions That Cause ED

A variety of neurologic conditions can cause ED. The most common of these are spinal cord injury, lumbar disk disease, stroke, Parkinson's disease, multiple sclerosis, Alzheimer's disease, and pituitary disease (pituitary adenoma). In addition, certain surgical procedures, such as radical prostatectomy for prostate cancer and surgery for rectal cancer, can injure the pelvic nerves. The incidence

Table 16. Medications That May Cause Erectile Dysfunction

of ED after radical prostatectomy varies according to whether the patient experienced ED before surgery and whether a nerve-sparing procedure was performed. Reported rates of ED after bilateral nerve-sparing radical prostatectomy range from 18 to 82%. Other factors unrelated to disease or surgery can also cause ED. For example, long-distance bicycle riding on bicycles with small, hard seats has been implicated as a cause of ED, possibly by nerve or vascular compression.