Neurologic Testing

Content written by Irwin Goldstein, MD

A functional nervous system is necessary for men’s genital tissue responsiveness and important for a man’s overall sexual health. The standard sexual medicine physical examination of the man with sexual health concerns thus emphasizes the integrity of the nervous system (somatic sensory and motor; and autonomic parasympathetic and sympathetic) as assessed by genital neurologic examination. The neurological examination should be part of the biologic-focused evaluation of all men with sexual health problems. Abnormal findings on initial physical examination may prompt further neurological testing, such as referral to a neurologist or neurosurgeon/spine specialist to obtain more detailed evaluations such as genital-cerebral evoked response testing (electrophysiological evaluations) and magnetic resonance imaging of the central nervous system. It is important to rule out signficant neurologic disease as the basis for a man’s sexual health concerns, or to confirm a neurologic cause for the sexual health problem, particularly in men with known neurologic disease, such as diabetes or multiple sclerosis. Neurologic impairment has been implicated in the cause of hypoactive sexual desire disorder, impaired erectile function, and ejaculatory/orgasmic dysfunction, in men with sexual dysfunction and diabetes.

Currently the sexual medicine physical examination focuses on the integrity of the somatic sensory and motor examination because conclusions concerning the integrity of the autonomic nervous system cannot be reached from genitourinary physical examination findings. Standardized neurological evaluations exist for all parts of the body, such as the lower extremity examination, and also exist for the men’s genitalia, including sensory exam, motor exam, and genital reflexes. Somatic innervation (sensory and motor) of the man’s genitalia is mediated via branches of the pudendal nerve. The pudendal nerve, derived from the second through fourth segments of the sacral spinal cord, provides critical sensation to all the erogenous areas in a man’s genitalia and critical motor function to the pelvic floor muscles, including the urinary and anal sphincters. The three branches of the pudendal nerve include the right and left dorsal nerve of the penis (sensory to the penis shaft and glans), the right and left perineal nerve (sensory to the scrotum and the perineum), and the right and left inferior rectal nerve (sensory to the perianal skin).

Neurologic assessment of the autonomic innervation of the genital organs, mediated via branches of the thoracolumbar (sympathetic), and sacral (parasympathetic) outflow tracts may be objectively assessed indirectly by measuring changes in genital blood flow as implied by changes in peak systolic and end-diastolic velocity measurements during duplex Doppler ultrasound of the cavernosal arteries pre-and post-sexual stimulation. In general, however, the autonomic nervous system contributions to the man’s genital organs have not yet been well characterized.

Neurologic testing is typically performed in a quiet room at a controlled temperature of 21–23°C. The innervation of men’s genital is bilateral and somatic innervation does not cross the midline. Thus somatic testing of a man’s genitals should be tested on both the right and left sides.

The sensory genital neurologic exam in a man with sexual health problems elicits information concerning sensory pudendal nerve integrity. Testing is performed on the pubic bone area (dorsal nerve branches of the pudendal nerve), scrotum (perineal nerve branches of the pudendal nerve), and perianal areas (inferior rectal nerve branches of the pudendal nerve). Subjective assessment of peripheral neuropathy is based on the man’s response to pinprick (21 gauge, one inch sterile needle) and light touch (cotton ball) sensation. Objective assessment of peripheral neuropathy is based on quantitative sensory testing examination using vibratory (biothesiometry), and hot and cold thermal sensory thresholds. Quantitative sensory testing involves the administration of quantified stimuli, vibration or hot or cold temperature, in controlled way, so that the subject defines the minimum sensory threshold by indicating the onset of the perceived sensation. Quantitative sensory testing is a repeatable, and valid descriptor of a man’s sensory state that has been used to assess sensory function for other neuropathies. There are no age-corrected normograms for thresholds of vibratory, hot, and cold thermal sensations for the penis. A-beta fibers are the largest nerve fibers, and mediate touch, mild pressure, sensation of joint position and vibration. Biothesiometry thus measures the integrity of the A-beta fibers. A-delta fibers are smaller nerve fibers that mediate sensation of cold and first components of pain sensation. Cold thermal testing thus measures the integrity of the A-delta fibers. C fibers are the smallest and slowest of the nerve fibers, and mediate heat sensation, main component of pain sensation and subserve most of autonomic peripheral functions. Hot thermal testing thus measures the integrity of the C fibers. For quantitative sensory testing, the control or non-genital reference site is typically the right pulp index finger but other sites may be chosen. The test sites for the dorsal nerve branches of the pudendal nerve are the midline glans and right and left shaft of the penis. The test sites for the perineal nerve branches of the pudendal nerve are the right and left sides of the scrotum. The test sites for the inferior rectal nerve branches of the pudendal nerve are the right and left perianal skin regions.

The motor genital neurologic exam in a man with sexual health problems exam elicits information concerning motor pudendal nerve integrity related to strength of pelvic motor contraction and ability to sustain the pelvic floor contraction capabilities. Objectively, an anal manometry device can be utilized to record the strength of pelvic motor contraction directly in cm/H20 contraction and the ability to sustain the pelvic floor contraction in seconds.

The sacral reflex genital neurologic exam in a woman with sexual health problems exam elicits information concerning the integrity of the afferent and efferent arms of the bulbocavernosus re?ex (the afferent arm is the sensory dorsal nerve of the penis, and the efferent arm is the motor perineal nerve) and the anal wink reflex (the afferent and efferent arms both arise from the inferior rectal nerve). All arms of these reflexes are branches of the pudendal nerve. An intact sacral reflex indicates that both sensory and motor arms of the re?ex are intact. For the bulbocavernosus re?ex, the index finger of one hand is placed in the perineum overlying the bulbocavernosus muscle at the crus of the penis. A short-lived squeeze of the glans penis with the opposite hand will elicit contraction of the bulbocavernosus muscle. The anal wink reflex is performed by using the wooden shaft end of the cotton tipped applicator to touch the perianal skin near the anus at the right and left sides. A brief contraction of the anal sphincter will be noted.

At the present time, sexual medicine physical examination that involves a detailed neurologic examination of men with sexual health problems is the most safe and effective means of assessing for neurologic causes of their sexual health concerns.

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