Dissociation between electrical and mechanical bulbocavernosus reflexes.

AIMS: To record reflex motor responses, elicited by mechanical stimulation of the penis or clitoris, in each bulbocavernosus muscles and to compare left and right reflex pathways in normal subjects, then to compare electrical and mechanical responses in various neurological diseases. METHODS: Two groups of patients were studied: 22 patients without neurological disease considered as normal subjects; and 25 patients with neurological disease (three multiple sclerosis, six spina bifida, nine conus medullaris syndrome, three peripheral neuropathies, two lumbosacral lesions, one multisystem atrophy, and one syringomyelia). Electrical bulbocavernosus reflex (EBCR) was evoked by orthodromic stimulation of the dorsal nerve of the penis at the penile base or the clitoris. Mechanical bulbocavernosus reflex (MBCR) was elicited with an electromechanical hammer, tapping directly on the clitoris zone or on the ventral part of glans penis. For EBCR and MBCR, bulbocavernosus muscle contractions were successively recorded in the left and in the right side with a needle inserted under visual guidance. RESULTS: Mean left mechanical latency was 31.7 msec (SD = 4.5) and right one 31.6 msec (SD = 3.8). The reproducibility of the responses was excellent (P < 0.0001). ). The mean difference between left and right latencies was 2 msec (SD = 1.2). In the neurological group, 22 EBCR (six right, nine left, seven bilateral) and 19 MBCR (eight right, nine left, two bilateral) were considered abnormal. The mean reflex latencies in patients with neurological lesions (lower motor neuron lesions) were statistically longer (P < 0.0001) than in normal subjects. Exact concordance (side of lesion) between MBCR and EBCR was observed in 15/25 cases (60%), poor concordance (presence of a sacral reflex alteration) in 3/25 (12%) cases, and in 7/25 (28%) cases there was a significant difference between the two techniques. CONCLUSIONS: MBCR may provide a good alternative for electrical stimulation and can be used to evaluate urinary disorders when a neurological etiology is suspected. However, the presence of false negatives with MBCR suggest that it may be more useful as a screening test.

Bulbocavernosus muscle responses after suprapubic stimulation: analysis and measurement of suprapubic bulbocavernosus reflex latency.

Our objective was to describe pelvic floor responses with measurement of reflex latency after suprapubic mechanical stimulation. Twenty-one patients without neurological disease were studied. They were 14 women and seven men. The mean age was 51 (SD = 14.2). Motor responses were recorded with a needle electrode inserted in the left bulbocavernosus muscle. Stimulation was delivered with an electromechanical hammer, tapping directly on the suprapubic area. A polyphasic muscular response was always easily elicited in all patients. The man latency was 67.5 milliseconds (SD = 14.7). The reproducibility between the first and second mechanical responses was good with no statistical difference (r=0.966;P = 0.0001). In three patients who underwent cystometry, no rise in detrusor pressure was observed during mechanical stimulation of the suprapubic area. Our study clearly demonstrates a suprapubic bulbocavernosus reflex (SBR). Tapping the suprapubic area is a strong stimulus, reflexively mediated, used in the management of neurogenic bladder to determine a bladder contraction. However, the reflex consisting of pelvic floor muscle contraction after suprapubic stimulation was not specifically studied in humans. Many arguments can be put forth for a polysynaptic reflex (polyphasic response, habituation and short latency of the reflex, mean latency in the habitual values of R2 responses after electrical stimulation of the dorsal nerve of the penis). We hypothesize that the true stimulus is the stimulation of the bladder wall tensoreceptors, the integration level of the SBR is the sacral segments and the efferent limb the pudendal nerve, and afferent pathways could be conducted by pelvic nerve fibers. Competition between a preponderant (or exaggerated) SBR and a bladder contraction after suprapubic tapping may constitute an equivalent of detrusor-sphincter dyssynergia in some suprasacral bladders.