Desire

Desire or sexual interest (libido) refers to the extent that an individual responds to or seeks out erotic stimuli. This varies with time and circumstances, and its measurement depends on self-ratings of such items as the frequency of spontaneous sexual thoughts, the excitement provoked by them, and the resulting behavioral response. Desire is enhanced by sexual activity itself, exciting circumstances, new sexual partners, hypomania, and certain focal brain lesions (particularly of the frontal and temporal lobes). Depressed patients may develop more than their premorbid levels of sexual desire in response to antidepressant medication and patients with Parkinson disease in response to dopaminergic therapy. Sexual interest may be lowered by lack of opportunity, age, malnutrition, certain addictive or sedative drugs, debilitating illness, depression, epilepsy, and certain focal brain lesions.

Animal experiments have revealed dopaminergic-stimulating and serotonergic-inhibiting mechanisms controlling sexual interest. Androgens are necessary for normal libido, although there are some uncertainties related to this issue. In women, sexual desire is also associated with levels of free testosterone.

The rhinencephalon, including the limbic cortex, is important for sexual desire and behavior. The basal hypothalamus is particularly relevant; it is affected by tissue levels of the sex steroid hormones, and lesions involving it may lead to loss of desire. The medial preoptic area is involved in regulating sexual motivation and performance, and dopamine may regulate penile erection at this level. A functional magnetic resonance imaging (fMRI) study of sexual interest in men (by comparing erotic to sport clips) showed activation in the right parietooccipital sulcus, the left superior occipital gyrus, and the precentral gyri. Functional imaging studies have demonstrated that the ovulatory cycle influences sexual interest and that activations in relevant brain areas are relatively greater in premenopausal than menopausal women.

Arousal

Sexual excitement results from genital stimulation, other sensory stimuli, or sexual ideation. The glans in both genders has a high receptor density: up to 80 to 90 percent of the nerve endings are free in the most superficial layer of mucosa. There are also corpuscular-type endings beneath the mucosal layer. The receptors are of two types: slowly adapting distally and rapidly adapting proximally, with afferent C and A delta fibers. Surrounding the cavernous bodies are large nerve endings that resemble onions, with thick lamellae and a central nerve fiber connected to thick, myelinated nerve fibers. These nerve endings respond to deep pressure and vigorous movement. Receptors close to the cavernous bodies are influenced by the amount of engorgement of cavernous tissues so that touch may be experienced simply as touch or as a sexual stimulus depending on the degree of engorgement.

Sensory information from the glans and skin of the penis and clitoris is conveyed through bilateral branches of the pudendal nerve (the dorsal nerves of penis/clitoris), as shown schematically in Figure 30-1 . The afferents from the root of the penis (and from the anterior part of the scrotum) join the ilioinguinal nerve. Genital afferents synapse in the spinal cord via interneurons with both somatic and autonomic motor neurons; those afferents destined for supraspinal structures travel in the anterolateral funiculus. “Erotically colored” sensations from the genital region are conveyed by the spinothalamic pathways, and patients with selective damage to these tracts may complain of anorgasmia and ejaculatory failure. Orgasmic sensation is blocked by bilateral anterolateral section of the spinal cord (cordotomy).

Somatic sensory afferents deliver information on tactile sexual stimuli that, after synapsing in the sacral spinal cord, induce local sexual responses (i.e., erectile and glandular responses). Sensory information also passes to suprasacral regions and is operative in other reflex activity, leading to awareness of sexual excitation. Both thalamic and cortical areas receive sensory input from the genitals, and sexual feelings may be elicited when such areas are stimulated. In the primary sensory cortex the genitals are traditionally thought to be represented in the parasagittal area; localization on the medial edge of the hemispheric convexity is claimed by a recent functional imaging study.

Somatosensory input from other body parts (“erogenic zones”) may—subject to somatic and individual psychologic factors and dependent on context—also lead to sexual excitement. Adequate sexual excitation can be achieved by stimuli delivered through cranial nerves. Although such “extrinsic” excitation—similarly to that achieved by stimulation of sexual organs—should also be called reflex (because there may be little “intrinsic” contribution to the excitatory response), it has traditionally been called “psychogenic.” Cortical and subcortical structures related to the limbic system elicit erection when stimulated. (Mental imagery is the “real” psychogenic activator.)

In men during visually evoked sexual arousal, regional cerebral blood-flow measurements by positron emission tomography have demonstrated activation of the inferior temporal cortex (a visual association region) bilaterally, of the right insula and inferior frontal cortex (regions processing sensory information and motivational state), and the left anterior cingulate cortex (involved in neuroendocrine function). Sexual arousal correlated with the magnitude of hypothalamic activation but was more pronounced in men than women. The occipitotemporal region was more activated in men, and the parietal lobe in women.

Sexual excitement leads to a complex response of the autonomic nervous system, and also to typical posturing in different species; in humans this behavior has been studied little but is understood to be influenced by psychosocial and cultural factors.

Parasympathetic efferents from the S2 to S4 spinal segments, traveling through the sacral plexus and cavernosal nerves, initiate erection ( Fig. 30-1 ). (The male erection has to be firm enough for vaginal penetration, and maintained throughout intercourse to bring about ejaculation, which in turn should deliver sperm to the uterine cervix.)

Blood flow in the penile artery, or the corresponding artery in the clitoris, increases. The smooth muscle of the cavernosal sinuses in the penile corpora relax, and the helicine arterioles branching from cavernosal arteries, selectively shunt blood flow to the lacunar spaces of the cavernosal bodies, filling them with blood. Subtunical venules are compressed so that corporeal venous return is restricted, resulting in increasing intracorporeal pressure. The pressure stabilizes at approximately systolic blood pressure, resulting in penile (and clitoral) tumescence and rigidity. Continued sacral parasympathetic activity maintains this erection.

The nerves of the corpora cavernosa have anatomic characteristics different from other nerves. The intracavernous nerves are located in fibrous tunnels, into which numerous fibrous bundles are attached. Contraction of striated pelvic floor muscles, the ischiocavernous muscles in particular, brought about through pudendal nerve activity, increases the rigidity of erection.

In women, parasympathetic activity causes clitoral erection, engorgement of the labia, and vaginal lubrication. The lubrication during sexual arousal is due to transudation through the vaginal wall. Another source is secretion from paraurethral glands (emptying into the urethra). Increased vaginal blood-flow, lubrication, and erection of cavernous tissue in the clitoris and around the outer part of the vagina are the female homologues of the male erectile response; indeed, lubrication occurs during rapid-eye-movement sleep in women. The response is dependent on innervation and a normal estrogen level.

In the periphery, the main proerectile transmitter is nitric oxide, which is co-localized with vasoactive intestinal peptide and acetylcholine; the main antierectile neurotransmitter is norepinephrine. The same mechanisms are responsible for clitoral erection.

Erections can still occur in men and animals after lesions of the sacral cord and pelvic nerves. This is due to the “alternative” proerectile pathway mediated through the hypogastric nerve. This explains the so-called psychogenic erections of paraplegics with conus or cauda equina lesions but preserved thoracolumbar segments. Similarly, women with injury to the sacral spinal cord and an ability to perceive pinprick in the T12 to L2 segments may retain the capacity for psychogenic genital vasocongestion. In women with complete spinal cord injuries and preserved sacral segments, such a response is as a rule obtained only by manual genital stimulation. Thus, the reflex–“psychogenic” dichotomy of the genital sexual response can be seen in both genders.

Inhibitory influences on the sexual response also exist. In nucleus paragigantocellularis a majority of the serotonergic neurons project to the spinal cord (traveling in the lateral funiculus) and provide tonic inhibition of sexual reflexes in the rat.

Orgasm

Seminal emission begins during arousal and, with continued sensory stimulation, orgasm is triggered, with ejaculation of the urethral contents resulting from the rhythmic phasic contractions of perineal and pelvic floor muscles. Ejaculation is effected by integrated sympathetic outflow from T11 to L2 segments traveling through the sympathetic chain and hypogastric plexus and along the pelvic and pudendal nerves, and by somatic efferents traveling through the pudendal nerves. Although the predominant neural control of the male accessory sexual organs is sympathetic (adrenergic and purinergic), the secretion of seminal fluid is under parasympathetic control. Sympathetic activity causes smooth muscle contraction in the seminal vesicles, vas deferens, and prostate to deliver seminal fluid to the posterior urethra; in the bladder neck to prevent retrograde ejaculation; and in the corpora cavernosa to cause detumescence. The latter “antierectile” activity is inhibited during erection through spinal coordination of reflex action.

The female orgasmic response consists of rhythmic contractions of pelvic floor muscles, the uterus, fallopian tubes, and paraurethral glands; expulsions from the paraurethral glands through the urethra may occur (so-called female ejaculation). Women may achieve orgasms by stimulation outside the genital region and probably do so more easily than men, but the most notable difference from men is that women may achieve multiple consecutive orgasms.

Motor innervation of the pelvic floor muscles as well as the ischiocavernosus and bulbocavernosus muscles is conveyed through pudendal nerve branches from below. However, the most relevant motor innervation of the levator ani (“pelvic floor”) muscle is directly from the sacral plexus via the levator ani nerve. Electromyographic recording of the pelvic floor muscles in women during vibratory clitoral stimulation shows intermittent activity associated with contractions on a background of continuous activity. During ejaculation in males, repeated bursts of electromyographic activity have been recorded that preceded and followed expulsion of semen. The sensation of orgasm, however, is not dependent on pelvic muscle contractions. Men reported that orgasmic sensation began before, and lasted longer than, bursts of electromyographic activity in the perineal muscles.

Orgasm can be separated conceptually (but not easily physiologically) from emission and ejaculation. Positron emission tomography (PET) imaging during orgasm has shown deactivation of frontal regions and the left temporal lobe; cerebellum and pons were activated ( Fig. 30-2 ). There were only minor differences between genders.

Functional neuroimaging during male and female orgasm. Orgasm-related effects were evaluated by comparing scans of orgasm with scans of sexual tactile genital stimulation. Activated (orange) and inactivated (blue) areas are the same in men and women. However, certain parts of the brain are more active only in men (green) or in women (red). LOFC, lateral orbitofrontal cortex; MOFC, medial orbitofrontal cortex: PAG, periaqueductal gray: rCBF, regional cerebral blood flow.

(From Georgiadis JR, Reinders AA, Paans AM, et al: Men versus women on sexual brain function: prominent differences during tactile genital stimulation, but not during orgasm. Hum Brain Mapp 30:3089, 2009, with permission.)

After orgasm (during the “resolution” or “refractory” phase), fMRI revealed activation of amygdala and the temporal lobes, and—for a short period—of the septal area.

Anorgasmia is very rare in neurologically normal men, but 13 percent of women between the ages of 18 and 26 years have never achieved orgasm, with the incidence declining to a minimum of 3 percent in women between the ages of 51 and 64 years.

Ejaculation can be absent with an intact orgasm in lesions of the hypogastric plexus and under the influence of some drugs.

Topographic Anatomy of Nerves in the Pelvis

The topographic anatomy is important as preservation of the peripheral nerves related to sexual (and bladder and bowel) function during abdominal and pelvic surgery is necessary for good postoperative results. In the pelvis and abdomen, autonomic structures related to genital innervation are situated in the retroperitoneal space. The superior hypogastric plexus is located anterior to the aortic bifurcation at the level of the fifth lumbar vertebral body and sacral promontory between the common iliac arteries. It divides caudally into the right and left hypogastric nerves. Within the pelvis, these nerves become the inferior hypogastric (pelvic) plexus, which is joined on each side by the pelvic nerves. In males, the inferior hypogastric plexus is lateral to the rectum, seminal vesicle, prostate, and the posterior part of the urinary bladder ( Fig. 30-3 ). The lesser and greater cavernosal nerves originate from the anterior part, are joined by fibers from the pudendal nerves, and pass below the pubic arch. In females, the inferior hypogastric (pelvic) plexus gives off uterine nerves, branches for the vagina and cervix, and connections with the paracervical plexus.

Anatomy in males of the pudendal nerve (indicating its vulnerability to compression during cycling), and of the pelvic plexus and cavernous nerves (indicating their vulnerability during perineal or pelvic surgery).

Awareness of the anatomy, careful surgical technique and specific intraoperative “mapping” and “monitoring” procedures have been suggested to preserve neural structures relevant for sexual function.

Change in Sexual Function with Aging

There is great variability of sexual functioning in the elderly. The frequency of intercourse as a rule decreases; nevertheless, 26 percent of those aged 75 to 85 years report sexual activity during the past 12 months. Males need more time and stimuli to achieve erection and orgasm. They have a decreased sensation of impending ejaculation and decreased ejaculatory volume. Their refractory period after detumescence is prolonged.

Hormonal changes in menopause lead to decreased libido and thinning of the vaginal wall with decreased elasticity and lubrication. Decreased sexual thoughts and frequency of intercourse after menopause are more closely correlated with testosterone than estrogen levels, but so far most studies have failed to demonstrate a clear relationship between low sexual desire and serum testosterone.

History

The history should include details of neurologic disease as well as any past history of urologic/gynecologic, cardiovascular, endocrine, psychologic, and psychiatric disturbances. History of disorders of the sex organs, trauma and surgical procedures, the use of prescription drugs, smoking and alcohol habits, and possible drug abuse should also be elicited. The patient’s sexual expectations, needs, and behavior should be defined as well as any misconceptions. Before diagnosing dysfunction of sexual organs, the level of actual desire should be established. The term hypoactive sexual desire disorder (HSDD) is used to define a persistent or recurrent reduction in desire for sexual activity, alone or with a partner, with inability to respond to sexual cues that would be expected to trigger a sexual response; symptoms need to be associated with personal distress. If present in men, it may be associated with impotence; in women it often occurs with the female sexual arousal disorder (FSAD), which is a persistent or recurrent inability to attain or maintain sufficient sexual excitement that causes personal distress.

Men should be asked about erectile function (the occurrence of nocturnal erections, morning erections, and erections evoked by genital, visual, auditory, or psychogenic stimuli) and women about vaginal lubrication. The nature of ejaculation should be determined, and in particular whether it is premature, retarded, absent, or dribbling (i.e., emissions occur through the urethra without the activity of pelvic floor muscles). Retrograde ejaculation, described as “dry ejaculation,” means that ejaculum has entered the bladder. Finally it should be clarified whether the patient can achieve orgasm, and the quality of orgasmic sensations and experiences should be noted. In some circumstances it may be helpful to interview the patient’s partner.

Formal questionnaires can be used to obtain standardized information on male sexual function. These questionnaires mostly focus on erectile dysfunction (the persistent inability to develop and maintain an erection sufficient for satisfactory sexual activity). The impact on quality of life is covered by another inventory. Questionnaires have also been formulated to assess sexual function in women, for instance the female sexual function index. Formal questionnaires are particularly relevant in research.

Clinical Examination

Sexual development, body length and weight, changes in pigmentation and body hair, and the presence of galactorrhea should be noted. The external genitalia should be examined. Palpation of peripheral pulses (arms, legs, penis), auscultation of the heart, and blood pressure measurement are recommended.

A standard neurologic examination, with inspection of the lower back (for nevus, hypertrichosis, or sinus), the feet (for deformity or muscle atrophy), and the anogenital area may reveal signs of underlying neurologic disease. Examination of the anogenital region involves palpation of the bulbocavernosus muscles in the male, testing for voluntary contraction (“move the penis”) and reflex contraction. The anal sphincter (also levator ani) is palpated for tone, voluntary contraction, and reflex contraction in both sexes by rectal examination. The cremasteric reflex (the L1 segment) and the bulbocavernosus and anal reflexes (S2 to S4/5 segments) should be tested.

Investigation of Genital Reaction and Arousal

In men, spontaneous and physiologically induced erection can be studied with a variety of techniques. Spontaneous nocturnal penile tumescence and rigidity can be measured in the sleep laboratory using mercury strain gauges (measuring penile expansion), visual inspection, measurement of buckling force (for assessment of rigidity), and polygraphic confirmation of sleep phases. Continuous monitoring of nocturnal penile tumescence and rigidity can be obtained by a rigidometer during normal sleeping conditions at home and also during daytime napping or in the awake, sexually stimulated state. Various low-cost screening tests for nocturnal penile expansion have been proposed, but their validity is questionable. Testing for nocturnal erections, however, does not reliably distinguish psychologic from central nervous system (CNS) causes of erectile dysfunction, as has been suggested by studies in men with multiple sclerosis. The aforementioned testing remains mainly of research interest.

An intracorporeal penile injection of a vasoactive substance, such as prostaglandin E ₁ , will induce an erection (in the absence of major vascular pathology), thus strengthening the suspicion of a neurogenic or psychogenic cause of erectile dysfunction. Intracorporeal injection of vasoactive agents has been proposed as an established diagnostic tool in patients undergoing assessment for possible neurogenic erectile dysfunction and is safe when performed by experienced physicians, with an acceptable complication rate.

Suspected vasogenic erectile dysfunction may require the testing of penile vasculature (blood pressure and vascular competence) by a urologist. The purpose of testing should always be defined; pharmacologic testing may be sufficient for the majority of patients, and invasive tests reserved for those in whom surgery is contemplated.

In women, both direct and indirect methods are used to measure blood-flow changes in the labia and vagina. Noncontrast dynamic magnetic resonance imaging (MRI) can assess female sexual arousal quantitatively. All these tests are only of research interest; it has been stressed that vaginal vasocongestion to erotic stimuli may be unaccompanied by erotic feelings, and subjective indices should therefore be obtained when physiologic measurements are made.

Investigations of Neurologic Function

Functional tests are direct extensions of the clinical examination. Special devices and algorithms can be used for quantifying sensory perception on the genital organs and in the perineum. The measurement of vibratory perception (biothesiometry; measuring the vibration perception threshold) on the glans have been advocated for diagnosing sensory neuropathy in male and female patients. The vibration perception threshold on the penis (glans and shaft) in neurologically healthy men is similar to that of the feet, whereas in females this threshold (best measured on the clitoris, labia majora, and perineum ) is the same as in the hands. Tests evaluating small-fiber function (e.g., testing for penile thermal sensation) may be more informative about the neural control of erection.

Several neurophysiologic tests have been suggested for assessing sacral or suprasegmental lesions ( Table 30-1 ). Tests measuring conduction through somatic nervous pathways (motor, sensory, and reflex) might be expected to be useful because most lesions should involve both somatic and autonomic neural pathways, and abnormalities obtained on testing the former could be extrapolated to the latter. Even so, these tests are sensitive only to demyelination and not to axonal lesions, which predominate in clinical practice. Electromyography may demonstrate the activation patterns of striated muscles but is mainly used to differentiate normal from denervated (reinnervated) muscle, discussed in detail elsewhere. Controversy exists about the source and nature of the signals recorded in penile and clitoral electromyography, and the findings have no diagnostic relevance. The lumbosacral sympathetic system may be tested by the sympathetic skin response from the perineum (and penis).

The role in clinical practice of these and the other tests shown in Table 30-1 is limited. In terms of validity, experience, and available normative values, only electromyography (in muscles of the lower sacral myotomes) and the recording of sacral reflex responses and somatosensory evoked potentials to pudendal nerve stimulation are recommended. The patients with possible or probable neurogenic sexual dysfunction in whom such testing might yield a result relevant for diagnosis and prognosis (though rarely important for decisions on therapy) are those with suspected lesions in the peripheral sacral reflex arc. In these patients, support for the presence or absence of a neurologic lesion can be obtained; this may have medicolegal implications. The relationship between a neurologic lesion (or, for that matter, any neurophysiologic test abnormality) and sexual dysfunction is complex; in women with multiple sclerosis, for instance, latency of pudendal (and tibial) somatosensory evoked potentials failed to predict the extent of sexual dysfunction.

Hormone Measurement

When patients with sexual dysfunction have symptoms or signs indicating endocrine dysfunction, hormone assays—or rather, endocrinologic consultation—may be necessary. The hormones to be studied depend on the circumstances (sex, age, and onset and nature of symptoms).

Head and Brain Injuries

Some cognitive impairment, personality change, and sensorimotor disability often remain after traumatic brain injury and may be accompanied by sexual dysfunction as a consequence of either the cerebral lesion or psychosocial factors. Among patients with closed-head injury admitted for 24 hours or more, significant sexual dysfunction was found in 50 percent over a 15-year time span. Decreased or increased sexual desire, erectile failure, and retarded ejaculation may occur, at least in part as a consequence of post-traumatic pituitary dysfunction. Frontal and temporal lesions seem to result more often in sexual disturbances than parieto-occipital lesions. Hypersexuality, disinhibited and inappropriate sexual behavior, sexually aggressive behavior, and changes in sexual preference sometimes follow basal frontal and limbic brain injury and may lead to sex offences. Bilateral anterior temporal lesions may result in the Klüver–Bucy syndrome with hypersexuality and pansexuality (i.e., sexual drive that is directed not only toward humans but also toward animals and inanimate objects).

Cerebrovascular Disease

Decline in desire and the frequency of intercourse after stroke is not unexpected ; the best predictor of decreased sexuality between partners is the degree of dependence in activities of daily living. From various studies, about 75 percent of patients who were sexually active before the stroke report a subsequent decrease in coital frequency. Late outcome studies are scant; poor sexual functioning may persist even with otherwise good improvement.

Many men (up to 65%) have erectile dysfunction after a stroke. Erectile dysfunction has been associated with abnormal nocturnal tumescence. Orgasmic and ejaculatory dysfunction after stroke is also common; nevertheless, both erections and ejaculation may return within a year after stroke. Decreased vaginal lubrication and inability to achieve orgasm occur in female patients.

Sexual problems after a stroke may be complicated by other deficits, poor personal image, and lack of coping.

Patients and their partners may avoid sexual intercourse out of concern that another stroke may be precipitated. The heart rate during sexual activity may exceed 180 beats per minute in men and reach similar values in women; the workload during sexual activity is similar to that of climbing stairs or walking briskly. Although the exact risk of stroke during sexual activity is not known, it seems to be low. Patients and their partners may thus be reassured that, in resuming sexual activity, the gains in most instances outweigh any slight risks. These issues should be addressed in counseling.

Hypersexuality after stroke has also been described, but seems to be rare.

Epilepsy

Epilepsy is associated with sexual problems, more often in men than women. Various types of abnormal behavior, hypersexuality, and, most commonly, hyposexuality have been reported, particularly in temporal lobe epilepsy. Satisfaction with life and sexuality is better in patients who are seizure free. The extent to which social and psychologic factors bear on sexual dysfunction is not clear. It is helpful to determine whether disturbances relate to seizures or occur during the interictal period.

Parkinson Disease

Bladder and bowel dysfunction in Parkinson disease are related to specific autonomic nervous system involvement, and the same is probably true for some of the abnormalities in sexuality. The dopaminergic system is intimately involved in neural circuits controlling desire and arousal. In comparison to controls, parkinsonian patients of both genders show a decrease in libido, frequency of intercourse, and ability to reach orgasm; in men, erection and ejaculation are disproportionately affected. Depression is common in parkinsonian patients and may affect sexual activity; its treatment may further compromise sexual function.

Sexual dysfunction is common even in young male parkinsonian patients. In comparison with age-matched controls, in whom the prevalence of impotence was 37.5 percent, the corresponding number in patients with Parkinson disease was 60 percent. An inability to maintain erections occurs in approximately half of parkinsonian men ; nocturnal and morning erections may be absent. Many men cannot ejaculate or reach orgasm. As for women with parkinsonism, vaginal tightness, involuntary urination, anxiety, and inhibition are more prevalent than in matched controls.

Tremor may be enhanced during sexual arousal, thereby limiting the patient. Muscle rigidity and bradykinesia may also make sexual activities more difficult and may be worse in the late evenings if dose scheduling is aimed at favoring daytime activities.

Dopaminergic treatment may result in an apparent increase, or normalization, of libido without corresponding improvement in parkinsonism. A true increase in desire and hypersexuality may occur as an adverse reaction to treatment with levodopa and, particularly, with dopamine agonists. On the order of 3 percent of treated patients demonstrate hypersexuality and probably even more do so among those treated with dopamine agonists ; this has been attributed to D3 receptor hyperactivation. Spontaneous erections have been reported in patients receiving levodopa. Apomorphine treatment may result in erections and benefits sexual function, as does cabergoline.

Deep brain stimulation of the subthalamic nucleus may have a positive influence on sexual well-being in Parkinson disease, in that male (but not female) patients are reportedly more satisfied with their sexual life. Hypersexuality has been reported as a side effect.

Multiple System Atrophy

Erectile dysfunction is an early sign of multiple system atrophy (MSA) and precedes bladder dysfunction and orthostatic hypotension. In a retrospective study of 46 men, 96 percent had erectile dysfunction at the time of diagnosis; it occurred alone as the first symptom in 37 percent and was part of the presenting symptom-complex in 59 percent. Erectile dysfunction usually began several years before the onset of other neurologic symptoms, often in patients in their early 50s or late 40s. By the time of diagnosis, 30 percent of male patients were also unable to ejaculate. In women, reduced genital sensitivity (as compared to parkinsonian patients and controls) has been reported.

MSA patients have a decrease in desire, the ability to reach orgasm, and the frequency of intercourse. They may, however, develop hypersexuality with dopaminergic treatment.

Other Extrapyramidal Disorders

In families with Huntington disease, members who ultimately develop the disease tend to have more children than those who are spared. Approximately 10 percent of patients with Huntington disease have increased sexual activity, sometimes associated with mania or hypomania. Habitual promiscuity and marital infidelity may be early or initial symptoms of the disease. However, patients may have difficulty in becoming sexually aroused. Paraphilias such as sexual aggression, exhibitionism, and pedophilia may occur.

Disinhibited sexual behavior is common in patients with Gilles de la Tourette syndrome, and increased sexual activity has been reported in patients with Wilson disease.

Hypothalamopituitary Disorders

Hypothalamopituitary dysfunction is usually caused by a pituitary adenoma; less common types of tumors in this region include craniopharyngiomas, meningiomas, optic gliomas, hypothalamic hamartomas, and metastases. Three-fourths of patients with hypothalamopituitary tumors have decreased or absent libido at the time of diagnosis. The figures are higher for large tumors that extend into the suprasellar region than for intrasellar tumors. Decreased libido (related to low serum testosterone levels) is also the first symptom in most men with small pituitary tumors and hyperprolactinemia, but is not a symptom for which patients commonly seek medical advice. Hence, the diagnosis is usually postponed until other symptoms appear, and it may be as long as a decade after the onset of changes in sexual behavior before the pituitary tumor becomes apparent. Erectile dysfunction is also common but, because of reduced sexual interest, is less distressing.

Most women with hypothalamopituitary disorders have amenorrhea. Women with hypoprolactinemia reportedly complain more commonly of loss of sexual desire than those with normal serum prolactin levels.

A low serum testosterone level in patients with erectile dysfunction does not necessarily signify a space-occupying lesion in the hypothalamopituitary region: a neuroimaging study of 164 impotent men with repeatedly low serum testosterone levels detected potentially serious lesions (pituitary lesions greater than 5 mm or any hypothalamic lesion) in 11, including 5 pituitary microadenomas (5 mm or more), 4 pituitary macroadenomas, and 2 hypothalamic lesions.

Multiple Sclerosis

Disturbances of sexual function are common in patients with multiple sclerosis, regardless of gender, and affect eventually the majority of patients. Sexual dysfunction is proven to decrease the quality of life in patients. Most such disturbances relate to spinal cord involvement and are generally, but not always, associated with urinary symptoms and lower limb involvement. Sexual dysfunction has also been correlated with destructive lesions in the pons, as detected by magnetic resonance imaging, in patients with relapsing-remitting multiple sclerosis.

Erectile dysfunction is rare initially, but becomes more common with evolution of multiple sclerosis. Interest in resuming sexual activity persists in 75 percent of patients. Spontaneous improvement in erectile function sometimes occurs. Problems with ejaculation are frequent and are often coupled to the erectile dysfunction. Anorgasmia has been correlated with evidence on magnetic resonance imaging of brainstem and corticospinal abnormalities as well as with total area of lesions.

Decreased vaginal lubrication and sensory disturbances involving the genital region (hypoesthesia, hyperesthesia, and different types of pain) are common and may be apparent already in the early stages of multiple sclerosis. Sacral-segment dysesthesias may be so severe that patients are unable to bear direct genital or nongenital contact. Electrodiagnostic data—cortical evoked potentials of the dorsal nerve of the clitoris —suggest that pudendal somatosensory input is necessary for female orgasmic function, and that this may be disturbed even in early MS.

Some patients experience decreased libido; emotional and cognitive disturbances may be contributory. Increased sexual desire occasionally constitutes a problem. Other symptoms related to multiple sclerosis, such as fatigue, depression, cognitive dysfunction, spasticity in the lower limbs, urinary and bowel disturbances, and the use of aids to manage incontinence, can inhibit sexuality, as can paroxysmal motor and sensory disturbances triggered by sexual intercourse.

Lesions of the Spinal Cord

A spinal cord injury (SCI) or lesion may lead to major neurologic deficits that in men initially often overshadow sexual disturbances such as a loss of normal erectile and ejaculatory function and of the ability to procreate naturally. For women, the resulting sexual dysfunction is often regarded as less limiting but is definitely important. The effects on erection, ejaculation, vaginal lubrication, and orgasm relate to the level and completeness of the lesion.

After complete cord transection, reflex function in all segments of the isolated spinal cord is completely lost (spinal shock) for a variable period lasting from a few hours to several weeks. Incomplete or slowly developing lesions may be associated with little or no spinal shock. The male genital reflexes (reflex penile erection and the bulbocavernosus and cremaster reflexes) are abolished or profoundly depressed during the period of spinal shock, and erectile and ejaculatory functions are abolished. Because of the occurrence of spinal shock, it is usually impossible to predict the extent or severity of sexual dysfunction, including whether erectile and ejaculatory functions will recover, in men within the first weeks after injury. With complete lesions of the spinal cord, the penis may become enlarged and semierect from passive engorgement of the corpora cavernosa due to paralytic vasodilation after the interruption of vasoconstrictor fibers in the anterolateral tracts of the spinal cord. As spinal shock subsides, reflex activity and spasticity may develop in the lower extremities and reflex functioning is regained of the bladder and bowels. In patients with upper motor neuron lesions, the erection reflex becomes part of the autonomic function of the isolated cord and may appear with tactile stimuli of various types and intensity, including stimuli to the penis, independent of cerebral participation and before the reflex responses of skeletal muscles are fully developed.

With complete destruction of the lower sacral spinal cord segments (the conus medullaris), reflex erection and lubrication are usually lost and the striated ejaculatory muscles are paralyzed. With spinal cord lesion between the level of the lower thoracic segments and the conus, both cerebral and reflex erection and lubrication may be possible, even though the patient cannot feel the sexual organs. Loss of sacral sensation does not necessarily imply anorgasmia. Although ejaculatory contractions cannot be felt when a complete lesion of the spinal cord exists above the conus, autonomic components of the orgasm can be experienced. Hyperesthesia often occurs just above or at the level of the spinal cord lesion, and may be useful as an erogenous zone. Although bladder, bowel, and sexual dysfunction often coexist, this is not necessarily the case; sexual function may be preserved in spite of severe neurogenic bladder dysfunction, presumably owing to preservation of the thoracic sympathetic outflow.

A meta-analysis of 24 studies of more than 2,500 men with spinal cord injuries showed that a median of 80 percent (range, 54 to 95%) reported spontaneous erections. The percentage of men reporting ejaculation without therapeutic assistance was much lower (median, 15%; range, 0 to 52%). Fewer (26%) of the patients with complete lower sacral lesions had erectile capacity than those with complete upper cord lesions or incomplete lesions at any level (90 to 99%). However, there is much individual variation, and an accurate prognosis for future sexual function may not be possible in individual cases.

Patients with incomplete spinal cord injury retain the ability for psychogenic genital vasocongestion if pinprick sensation is preserved in the T11 to T12 segments; only reflexogenic responses are obtained in those with complete spinal cord injury. After spinal cord injury, women menstruate and are able to conceive and give birth, although those with a paralyzed pelvic floor are at risk of overstretching and perineal tears. Autonomic hyperreflexia ( Chapter 8 ) may occur in those with a lesion above T6–7.

Preoccupation with future sexual performance occurs early after injury, and it may be easier for men to accept motor deficits than sexual problems. Sexual readjustment depends on the individual, on previous sexual habits, and on the cooperation of partners. In one study, sexual readjustment was closely and positively correlated with a young age at injury, frequency of sexual intercourse, and willingness to experiment with alternative sexual expressions. Physical and social independence and a high mood level were further positive determinants of sexual adaptation after injury.

The semen of men with spinal cord injury is characterized by small volume, low sperm count, and low sperm mobility. Reduced fertility cannot therefore be attributed completely to ejaculatory dysfunction. Collection of semen very early after the injury makes it possible to store semen of good quality for future insemination.

The ability to ejaculate by masturbation or sexual intercourse is impaired in most men with severe injury of the spinal cord; consequently, pregnancies caused by such men are rare without medical intervention. Ejaculation can be provoked in many paraplegic men through vibratory stimulation or electrostimulation (with careful blood pressure monitoring because of the risk of autonomic dysreflexia). Repeated vibration-induced ejaculations result in increased volume of semen, a larger number of motile sperms, and improved sperm penetration capacity. Insemination with autologous semen obtained in such a way has resulted in pregnancies.

Orgasms may occur in men with spinal cord injury but may differ from those that occurred before the injury. Women with such injuries may also achieve orgasm; indeed, some women with apparently complete lesions can do so, perhaps because of afferents from the cervix traveling with the vagus nerve. Latency to orgasm is greater in women with spinal cord injury than in normal subjects, but the descriptions of orgasm are indistinguishable.

Cauda Equina Lesions and Lumbar Stenosis

Although complete lesions of the cauda equina damage the parasympathetic erectile pathways to the penis, a number of men (approximately one-fourth) are still able to achieve an erection psychogenically, mediated probably by the sympathetic erectile pathway involving the hypogastric plexus. There are also ejaculatory disturbances (delayed or absent, but occasionally premature ejaculation), penile sensory loss, paresthesias, dysesthesias, and even pain syndromes. In a group of men with cauda equina lesions of differing causes and variable severity, only 15 percent reported normal sexual function. Women report loss of erotic sensation, dyspareunia, loss of lubrication, loss of feeling during vaginal intercourse, difficulties in achieving orgasm, and changes in the feeling of orgasm.

Involvement of lower sacral nerve roots by any process can lead to “positive” as well as “negative” functional symptoms. Sensory symptoms and deficits involving the genitals are not necessarily accompanied by impotence. Spontaneous erections on walking are occasionally reported in patients with symptomatic lumbar stenosis.

Spinal Malformations

Any type of dysraphism may be associated with neurologic symptoms that may include sexual disturbances, but data from large patient populations are lacking. Meningomyelocele as a rule gives rise, among other disturbances, to sexual dysfunction, depending on the severity of the malformation. Some boys have no genital sensations at all, with loss of erection and orgasm; some have isolated erections without emission. Loss of genital sensations is the major complaint in girls.

Erectile dysfunction may occur in patients with Arnold–Chiari malformations; the onset of sexual symptoms is generally after the development of other neurologic disturbances.

Localized Nerve Lesions

Trauma may cause pudendal nerve injury, leading to loss of penile sensation, dysesthesias, pain syndromes, and dribbling ejaculation because of perineal muscle denervation. Among long-distance cyclists, it was found in one study that 22 percent had penile sensory symptoms and 13 percent had erectile dysfunction; symptoms were transient but persisted for up to 8 months.

Erectile dysfunction may follow pelvic fracture, especially when urethral injury has occurred, owing to involvement of the neurovascular bundles. The peripheral autonomic nerves to the genitalia may be injured also by surgical procedures, leading to erectile and ejaculatory dysfunction in men and loss of lubrication in women. The sympathetic thoracolumbar fibers may be injured by retroperitoneal lymph node dissections. Pelvic plexus and cavernosal nerves may be injured by such operations as abdominoperineal resection for carcinoma, hysterectomy, radical prostatectomy, or sphincterotomy, thus significantly impairing the quality of life in patients after otherwise successful surgery (cf. Fig. 30-3 ). Surgeons are increasingly aware of the need to preserve relevant neural tissue even during radical surgery and have developed “nerve-sparing” operations.

Erectile dysfunction has also been reported after injection of sclerosing agents to treat hemorrhoids and hypersensitive bladder.

Diabetic Polyneuropathy

Diabetes is the most common cause of polyneuropathy in developed countries, and the most frequent type of neuropathy is the distal symmetric sensorimotor variety, in which small nerve fibers may be involved earlier than large fibers. This polyneuropathy is frequently accompanied by autonomic involvement, and dysautonomia is occasionally the predominant clinical presentation, with bladder, bowel, and sexual dysfunction. Hyperglycemia and some glycosylation products promote inactivation of nitric oxide and there seems to be a selective nitrergic neurodegeneration in diabetes. Further discussion of diabetic neuropathy is provided in Chapter 19 .

Sexual dysfunction, especially erectile dysfunction, is common in diabetic men. Erectile dysfunction has been reported in 9 percent of diabetic men aged 20 to 29 years, rising to 95 percent of diabetics by age 70. Overall the incidence in a population of 9,500 diabetic men (20 to 70 years old) was 38 percent. Patients had the onset of impotence within the first 10 years of their disease in 50 percent of cases. Men with diabetic polyneuropathy have fewer sleep-related erections, shorter tumescence time, diminished penile circumference increase, and weaker penile rigidity than do nondiabetic men. Erectile dysfunction is usually considered neurogenic when there are other signs of neuropathy, although alternative etiologic possibilities cannot be excluded. There is little correlation with neurophysiologic abnormalities in peripheral nerve function. Although the bulbocavernosus reflex latencies and penile (pudendal) evoked potentials are more often abnormal in impotent than potent diabetic men, neurophysiologic testing of pudendal nerve function is less sensitive in diagnosing neuropathy in impotent diabetics than limb nerve conduction studies.

In patients with cystopathy, retrograde ejaculation is sometimes an additional problem; failure of normal closure of the bladder neck by sympathetic activation during ejaculation leads to semen passing retrogradely into the bladder.

Among women, those with more diabetic complications have greater sexual dysfunction. A correlation in diabetic women of sexual dysfunction with the presence of neuropathy has not been found in all studies. Reduced sexual desire, decreased vaginal lubrication, and decreased capacity to achieve orgasm compared with age-matched controls have been reported.

Chronic Renal Failure

Male patients on hemodialysis have a similar prevalence of erectile dysfunction (71%) to patients on peritoneal dialysis (80%). Neuropathy is not the only possible cause; primary hypogonadism has been reported, and involvement of the testes also leads to low sperm counts and azoospermia. However, even in nondiabetic men with erectile dysfunction who were undergoing hemodialysis, the etiology was usually neuropathic rather than endocrinologic or vascular. On the whole, there is a tendency for preexistent erectile dysfunction to improve after transplantation.

Among women with uremia, one-half have decreased desire, and one-third have decreased lubrication; dysfunction improves after trans- plantation.

Other Acquired Polyneuropathies

Autonomic dysfunction, including erectile dysfunction, occurs in other peripheral neuropathies, including those due to infectious agents, chemical toxins, secondary amyloidosis, prescription or street drugs, and vitamin B ₁ or vitamin B ₁₂ deficiency, or those that are parainfectious or paraneoplastic. Autonomic involvement may lead to erectile dysfunction in the Guillain–Barré syndrome and may also occur in patients with chronic inflammatory demyelinating polyneuropathy. Reversal of erectile dysfunction and penile sensory loss may follow effective treatment.

In persons infected with the human immunodeficiency virus (HIV), peripheral nerve disorders occur commonly and may be accompanied by a dysautonomia. Slowed sural and dorsal penile sensory conduction velocities suggest that neuropathy is important in the genesis of erectile dysfunction in HIV-positive men. Counseling and treatment may be especially important in AIDS patients with sexual dysfunction, since the use of condoms often precipitates the problem, and men are therefore unwilling to use protection.

Hereditary Polyneuropathies

Erectile dysfunction and ejaculatory problems may occur in patients with hereditary sensory neuropathy and Charcot–Marie–Tooth syndrome. Erectile dysfunction also occurs in primary amyloidotic polyneuropathy and adrenoleukodystrophies. Men with hereditary motor and sensory neuropathy and electrophysiologically proven involvement of the pudendal nerves may nevertheless have normal sexual function.

Amyotrophic Lateral Sclerosis

Sexual function is normal in men with amyotrophic lateral sclerosis. Even when severe weakness makes intercourse impractical, erection and ejaculation are possible through partner masturbation, and the sensation of orgasm may be experienced as normal. These factors are highly relevant with regard to the patient’s quality of life and may be important in counseling patients and their partners.

Hereditary Neuromuscular Diseases

The early onset and progressive course of certain hereditary neuromuscular diseases may restrict psychosocial and psychosexual development and limit sexual activity. Nevertheless, the capacity for sexual satisfaction remains unaffected in many patients who survive to adulthood and consequently has led to more awareness of the need for appropriate counseling.

In Kennedy syndrome (X-linked bulbospinal muscular atrophy), gynecomastia is common and testicular atrophy, decreased libido, and erectile dysfunction may occur. Hypogonadism, diminished libido, erectile dysfunction, and amenorrhea occur in certain muscular dystrophies (myotonic dystrophy but also others) and in mitochondrial encephalomyopathies.

Adverse Sexual Reactions to Medications

Many medications used in patients with neurologic disorders have adverse effects on sexuality ( Table 30-2 ). At least until recently, however, the occurrence of sexual dysfunction was rarely monitored in clinical drug trials, and our data are collated from postregistration use, mostly uncontrolled studies and case reports. Further discussion of this aspect is beyond the scope of this chapter.

Table 30-2

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

Neurologic Complications of Cardiac Surgery Neurologic Manifestations of Nutritional Disorders Neurologic Complications of Chemotherapy and Radiation Therapy Neurologic Complications of Thermal and Electric Burns HIV and other Retroviral Infections of the Nervous System Neuromuscular Complications of General Medical Disorders

Stay updated, free articles. Join our Telegram channel

Join