OVERVIEW

Sexual disorders are extremely common. It has been estimated that 43% of women and 31% of men in the United States suffer from sexual dysfunction. In addition, lack of sexual satisfaction is associated with significant emotional distress (including depression and marital conflict) and physical problems (e.g., cardiovascular disease and diabetes mellitus). Individuals with sexual problems are often reluctant to seek assistance from a physician and may first experiment with any number of self-help methods. However, with the introduction of sildenafil (Viagra) and related compounds for the treatment of erectile dysfunction and the increased interest in pharmacological therapy for female sexual disorders, the frequency of complaints related to sexual dysfunction in primary care practice has risen to nearly 15% to 20% of visits. Nevertheless, the incidence of sexual problems in any medical practice is related to the frequency with which providers take a sexual history.

The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) classifies sexual disorders into four major categories. Sexual dysfunction is characterized by disturbances in sexual desire or psychophysiological changes in the sexual response cycle. Paraphilias are characterized by recurrent, intense sexual urges that involve unusual objects or activities. Gender identity disorders involve persistent cross-gender identification and discomfort with one’s assigned sex. Sexual disorders not otherwise specified are used to code disorders that are not classifiable into any of the other categories. All sexual disorders must cause clinically significant distress or an impairment of social function before a diagnosis can be made. Disorders are classified as primary when there has never been a period of satisfactory functioning or secondary when the difficulty occurs after adequate functioning had been obtained.

EPIDEMIOLOGY AND RISK FACTORS

Sexual disorders affect individuals across the epidemiological spectrum, and risk factors for them have been identified. Overall, the prevalence of sexual dysfunction is greater in women than it is in men. Sexual dysfunction increases with age, regardless of gender. Men and women with higher levels of education have fewer sexual problems and less anxiety about sexual issues. Co-existing medical conditions (including diabetes mellitus, cardiovascular disease, other genitourinary disease, and psychiatric/psychological disorders) and other chronic diseases are associated with a decline in sexual function in both men and women, as is diminished general health status. Among those with obesity and a sedentary lifestyle, weight loss and increased physical activity are associated with improved sexual function. The association between race and sexual dysfunction is more variable. There is a strong association between erectile dysfunction and vascular diseases. Recent evidence suggests an increased risk of erectile dysfunction among individuals who possess specific genetic mutations (e.g., polymorphisms in genes for nitric oxide synthase and Rho kinase) in molecular pathways responsible for resisting endothelial dysfunction. Sexual trauma for both sexes is associated with long-term negative changes in sexual function. A strong association exists between paraphilias and childhood attention-deficit/hyperactivity disorder (ADHD), substance abuse, major depression or dysthymia, and phobic disorder. The prototypical paraphiliac is young, white, and male.

PATHOPHYSIOLOGY

The ability of an individual to maintain adequate sexual function depends on complex interactions among the brain, hormones, and the vascular system. While the pathophysiological mechanisms of disease remain elusive for most sexual disorders, recent data suggest a central role for nitric oxide (NO) at the vascular level. In women, NO is thought to control vaginal smooth muscle tone; higher levels of NO are associated with increased vaginal lubrication. In men, NO allows for increased intrapenile blood flow, which facilitates erection. NO acts via the generation of cGMP, which has vasodilatory properties. PDE-5 inhibitors (the prototype of which is sildenafil) act to inhibit the degradation of cGMP, which prolongs the effects of NO.

Sexual dysfunction is best understood by having knowledge of the stages of the normal sexual response; these vary with age and physical status. Medications, diseases, injuries, and psychological conditions can affect the sexual response in any of its component phases, and can lead to different dysfunctional syndromes (Table 36-1). Three major models of the human sexual response have been proposed.

Table 36-1 Classification of Sexual Dysfunctions

Masters and Johnson developed the first model of the human sexual response, consisting of a linear progression through four distinct phases: (1) excitement (arousal); (2) plateau (maximal arousal before orgasm); (3) orgasm (rhythmic muscular contractions); and (4) resolution (return to baseline). Following resolution, a refractory period exists in men.

Kaplan modified the Masters and Johnson model by introducing a desire stage; this model emphasizes the importance of neuropsychological input in the human sexual response. The Kaplan model consists of three stages: (1) desire; (2) excitement/arousal (including an increase in peripheral blood flow); and (3) orgasm (muscular contraction).

Basson, who recognized the complexity of the female sexual response, more recently has proposed a biopsychosocial model of female sexuality that consists of four overlapping components: (1) biology; (2) psychology; (3) sociocultural factors; and (4) interpersonal relationships. This conceptualization has several important implications. First, it emphasizes the interplay of many factors in the stimulation of a woman’s desire or receptivity for sex. Second, it posits that intrinsic sexual desire and receptivity for sex (e.g., to achieve emotional closeness) are distinct entities, which may stimulate each other. (Thus, arousal may be prompted by nonsexual stimuli, which may then lead to actual sexual desire, rather than the reverse process.) Third, it suggests that a woman may still feel sexually satisfied in the absence of direct sexual desire. The fact that physical measurements of female arousal (such as increased vaginal secretions) are poorly correlated with sexual satisfaction lends support for Basson’s view.

Aging is associated with changes in the normal human sexual response. Men are slower to achieve erections and require more direct stimulation of the penis to achieve erections. Women have decreased levels of estrogen, which leads to decreased vaginal lubrication and narrowing of the vagina. Testosterone levels in both sexes decline with age, which may result in decreased libido.

CLINICAL FEATURES AND DIAGNOSIS

The diagnosis of a sexual problem relies on a thorough medical and sexual history. Physical examination and laboratory investigations may be crucial to identification of organic causes of sexual dysfunction. Many sexual disorders have both an organic and a psychological component. Physical disorders, surgical conditions (Table 36-2), medications, and use or abuse of drugs (Table 36-3) can affect sexual function directly or cause secondary psychological reactions that lead to a sexual problem. Psychological factors may predispose to, precipitate, or maintain a sexual disorder (Table 36-4).

Table 36-2 Medical and Surgical Conditions Causing Sexual Dysfunctions

Table 36-3 Drugs and Medicines That Cause Sexual Dysfunction

Table 36-4 Psychological Causes of Sexual Dysfunction

Physical Examination and Laboratory Investigation

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