Men reporting ‘numbness’ and ‘loss of sensations’ over the external genitalia present to urological and neurological services and the symptoms are often associated with emotional distress and a significant impact on quality of life.  In view of the complex innervation of the genitalia from the somatic (pudendal) and autonomic nervous system, a neurological cause for numbness should be suspected. This study aims to characterize the clinical features, neurological examination and neurophysiological assessment of a cohort of men reporting genital numbness.

This was a retrospective study evaluating men referred to a tertiary referral centre  (Department of  Uro-Neurology at The National Hospital for Neurology and Neurosurgery (NHNN), Queen Square, London) from January 2010 to June 2018 primarily with the complaint of “genital numbness”, “loss of sensation” and/or “loss of erotic sensitivity”.  Patients with known neurological disease were excluded.  
The following information were obtained: age, height, duration and characteristics of sexual difficulties, bladder and bowel symptoms, exposure to possible predisposing factors (medications, cycling, circumcision history and lichen sclerosus).  
The subjects underwent pelvic neurological examinations ( including sensory testing using von Frey hairs (vFH) and neurotip to examine touch and pain, respectively, and mapping of sensations of the penis, motor testing and reflexes) and pelvic neurophysiology tests (pudendal somatosensory evoked potentials (PSEP) (Keypoint neurophysiology system, Optima Medical Ltd)).

Fifty-four consecutive men (mean age=43.02(SD=(±10.32)) reporting genital numbness  (mean symptom duration year = 9.07 (SD= ±9.54)) were prospectively assessed between January 2010 and December 2016. Additional reported symptoms included erectile dysfunction (n=36 (66.67%)), ejaculatory dysfunction (n=32 (59.26%)), orgasmic dysfunction (n=37 (68.5%), abnormal sexual desire (n= 25 (46.3%)), lower urinary tract symptoms (n=20 (35.19%)) and bowel dysfunction (n=19 (35.19%)).  
The following potential predisposing factors were observed: exposure to SSRI (n=5 – 9.3%), exposure to finasteride (n=3 – 5.6%), history of circumcision (n=7 – 13%), prolonged cycling (n=8 – 14.8%), lichen sclerosus (n=8 – 14.8%). In 20 subjects (37%) it was not possible to identify a cause.
Examination with vFHs was performed in 47 subjects and demonstrated significant sensory impairment over the glans of the penis (dorsally and ventrally) (figure 1), compared with the shaft (p < 0.001), and there was a trend of significant sensory impairment over the ventral surface of the shaft, compared with dorsal shaft (p=0.066). The rest of the pelvic neurological examination (anal sphincter tone, anal sphincter voluntary and involuntary contraction, anal reflex and bulbocavernosus reflex) was normal in most patients; the anal sphincter tone was abnormal in 1 subject (1.9%) and the anal reflex was absent in 3 subjects (5.6%).
The mean latency of the P40 waveform in PSEP was 42.35 msec (SD=4.52) (n=41; figure 2) and the test was abnormal in 6 subjects, including absent response (n=1), prolonged response to more than 47.8 msec (n=3), and 7 msec PSEP P40 latency more than tibial P40 (n=2).

In most men presenting with genital numbness, sensory loss over the penis did not conform to a specific nerve distribution or sensory dermatome and neurophysiology testing was normal, suggesting a loss of erogenous sensations rather than sensory nerve damage.
Subjects presenting with loss of erogenous sensation may present with different types of sexual dysfunction, including erectile dysfunction, ejaculatory dysfunction, orgasmic dysfunction and abnormal sexual desire. Although the erogenous sensation was affected, sexual drive appeared to be preserved in 50% of subjects as the pathway responsible for sexual drive was not impaired.
The most common predisposing factors were exposure to SSRI or finasteride, history of circumcision, prolonged cycling, lichen sclerosus but in a significant percentage of subjects no cause could be identified. 
In a small percentage of patients the neurophysiological testing was abnormal, suggesting that the genital numbness was caused by nerve injury, therefore further investigations were required to explore an underlying neuropathy.

In most men presenting with genital numbness, sensory loss over the penis did not conform to a specific nerve distribution or sensory dermatome and neurophysiology testing was normal, suggesting a loss of erogenous sensations rather than sensory nerve damage. In a small percentage of subjects, genital numbness is associated with nerve injury and further investigations are required to explore an underlying neuropathy.