Neurophysiological investigation of diabetic impotence. Are sacral response studies of value?

[Urethral reflexes: A review]

INTRODUCTION

The urethrosphincter complex is involved not only in maintaining urinary continence, particularly during effort, but also for the achievement of a complete and effective micturition. Indeed, the urethra is not a simple passive channel for the evacuation of urine from the bladder to the urethral meatus, since its resistive capacities and its possibilities of modulation of the micturition reflex depend on its reflex role either as a sensory afferent or as a neuro-muscular effector. It also participates in many genito-sexual and ano-rectal réflexes.

MATERIAL AND METHOD

This review of the literature describes the various reflexes of the urethra as a sensory stimulus or a neuromuscular effector. All articles referenced in this review were obtained from articles indexed on Pubmed-Medline, using the keywords: "urethral reflexes; "reflex bladder"; "urination reflex"; "intravaginal; vaginal"; "anorectal; sphincter"; "Storage and voiding"; "reflexes sneezing"; "cough reflex". Other articles were selected through references of the articles issued from the first research. Only articles in English and French have been selected. The articles concerned animal and human experiments.

RESULTS

Eight hundred and sixty-four referenced articles were founded and a total of 75 articles were included, describing the various reflexes mediated by the urethra acting as a sensory afferent or mechanical effector. We differentiated the known data in humans and animals.

CONCLUSION

The urethra is a complex anatomical structure ensuring, through numerous reflex mechanisms, urinary continence. Urethral resistances are modulated during efforts and depends on the bladder capacity and the intensity of the efforts. During micturition, the coordination between the bladder and the urethra is mediated by reflex pathways organized at the cerebral, spinal and lumbosacral levels. The modulation of the micturition in term of efficacy and velocity, is due in part, to the re-afferentation of the spinal reflex by continuous stimulus of the urethral canal. Many of these reflexes are imperfectly described. Finally, the urethra is implicated in reflex loops of anal continence and sexual functions.

Bladder outlet obstruction triggers neural plasticity in sensory pathways and contributes to impaired sensitivity in erectile dysfunction

Lower urinary tract symptoms (LUTS) and erectile dysfunction (ED) are common problems in aging males worldwide. The objective of this work was to evaluate the effects of bladder neck nerve damage induced by partial bladder outlet obstruction (PBOO) on sensory innervation of the corpus cavernosum (CC) and CC smooth muscle (CCSM) using a rat model of PBOO induced by a partial ligation of the bladder neck. Retrograde labeling technique was used to label dorsal root ganglion (DRG) neurons that innervate the urinary bladder and CC. Contractility and relaxation of the CCSM was studied in vitro, and expression of nitric oxide synthase (NOS) was evaluated by Western blotting. Concentration of the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide was measured by ELISA. Partial obstruction of the bladder neck caused a significant hypertrophy of the urinary bladders (2.5-fold increase at 2 wk). Analysis of L6-S2 DRG sections determined that sensory ganglia received input from both the urinary bladder and CC with 5-7% of all neurons double labeled from both organs. The contractile responses of CC muscle strips to KCl and phenylephrine were decreased after PBOO, followed by a reduced relaxation response to nitroprusside. A significant decrease in neuronal NOS expression, but not in endothelial NOS or protein kinase G (PKG-1), was detected in the CCSM of the obstructed animals. Additionally, PBOO caused some impairment to sensory nerves as evidenced by a fivefold downregulation of SP in the CC (P ≤ 0.001). Our results provide evidence that PBOO leads to the impairment of bladder neck afferent innervation followed by a decrease in CCSM relaxation, downregulation of nNOS expression, and reduced content of sensory neuropeptides in the CC smooth muscle. These results suggest that nerve damage in PBOO may contribute to LUTS-ED comorbidity and trigger secondary changes in the contraction/relaxation mechanisms of CCSM.

Urethral sensory threshold and urethro-anal reflex latency in continent women

AIMS OF STUDY

The sensory evaluation of the lower urinary tract is summarized in the bladder proprioceptive sensitivity during cystometry. Experimental studies suggest that abnormalities of the urethral innervation and micturition reflex can be related to the presence of continence disturbances. This study aimed to measure the urethral sensory threshold and the urethro-anal reflex latency in healthy volunteers, establishing reading criteria, comparing the results and technique used with the literature and verifying the effect of physiological factors.

MATERIALS AND METHODS

Thirty healthy female volunteers were studied. They had an absence of genital or urinary complaints and had undergone no previous pelvic or vaginal procedures. The measurement of the urethral sensory threshold and urethro-anal reflex latency were performed as described.

RESULTS

The determination of the urethral sensory threshold and urethro-anal reflex latency were obtained in 96.6% of the volunteers. The electrophysiological parameters did not correlate with age, parity or number of vaginal deliveries. There was a positive association of the urethral sensory threshold with height. Technical aspects were considered and compared with those in the literature as well as the advantages and limitations of the method.

CONCLUSIONS

The measurement of the urethral sensory threshold and urethro-anal reflex latency presented consistent recordings. The urethral sensory threshold should be analyzed carefully in individuals with height above the population average. Subsequent observations are necessary to clarify their function in patients with continence disturbances and to measure the urethral function, but these values can be used as normal parameters for comparison.

Neurophysiologic studies of the penilo-cavernosus reflex: Normative data

AIMS

To determine normative values for the penilo-cavernosus reflex on single and double pulse electrical, and mechanical stimulation.

METHODS

All men without neurologic disorder, with normal neurologic examination, and with bilaterally normal quantitative electromyography of the external anal sphincter muscles referred for sacral neurophysiologic studies in the years 2003-2005 were included. The penilo-cavernosus reflex was studied on single and double electrical, and mechanical stimulation. Responses were detected by a needle electrode inserted consecutively into the left and right bulbocavernosus muscle. In each subject, latency of the response, and using electrical stimulation, the sensory threshold, reflex threshold and stimulation strength, were determined. Normative values were calculated using parametric statistics and optimal data transformations.

RESULTS

In all 26 men with minor non-neurogenic sacral dysfunction reflex responses were recorded using each stimulation technique. Minimal latencies of reflex responses (in msec) were 29.88 +/- 5.65 (upper limit: 39.4), 30.00 +/- 4.11 (36.0), 28.16 +/- 5.80 (35.5) on single electrical, double electrical and mechanical stimulation, respectively. Sensory thresholds (in mA) were 7.80 +/- 2.73 (upper limit: 14.5) and 6.08 +/- 2.30 (10.5), and reflex thresholds (in mA) 25.36 +/- 11.04 (upper limit: 49.6) and 12.78 +/- 6.06 (26.9) on single and double electrical stimulation, respectively.

CONCLUSIONS

The obtained normative values for latency on single electrical and mechanical stimulation were similar to those previously published. Additional data on latency on double electrical stimulation, and on the sensory and reflex thresholds on single and double electrical stimulation are expected to increase the diagnostic utility of the penilo-cavernosus reflex.

Evoked cavernous activity

PURPOSE

Corpus cavernosum electromyography has been widely done to evaluate autonomic dysfunction in patients with erectile dysfunction. We assessed the value of corpus cavernosum electromyography, evoked cavernous activity and penile sympathetic skin responses for their accuracy in determining autonomic involvement in cases of erectile dysfunction.

MATERIALS AND METHOD

We evaluated 75 men with erectile dysfunction by corpus cavernosum electromyography, evoked cavernous activity and penile sympathetic skin response tests at our neurourology laboratory. The etiology of dysfunction was vascular, neurogenic, psychogenic or mixed based on a detailed medical and sexual history, physical examination, electrophysiological and laboratory studies, penile color Doppler ultrasonography, and cavernosography and/or cavernosometry. Autonomic involvement was clinically assessed by systemic findings, such as orthostatic hypotension, impaired gastrointestinal motility, sinus dysrhythmia and secretomotor changes. A concentric electromyography needle placed in the right cavernous body was used to record corpus cavernosum electromyography and evoked cavernous activity. The right median nerve was stimulated electrically with 13 to 16 mA. to determine evoked cavernous activity and the penile sympathetic skin response. The latter response was recorded with silver disc electrodes placed on the left cavernous body. All tests were performed using an electromyography/evoked potential machine. We determined the relationships among corpus cavernosum electromyography, evoked cavernous activity and penile sympathetic skin response tests in respect to etiological factors.

RESULTS

The 56 patients with normal corpus cavernosum electromyography activity had also evoked cavernous activity and a penile sympathetic skin response except for 1 with no penile sympathetic skin response but evoked cavernous activity. None of these patients had autonomic neuropathy. Of the 19 patients without corpus cavernosum electromyography activity 11 had evoked cavernous activity, including 10 with no autonomic neuropathy. The remaining 8 patients had no evoked cavernous activity, of whom 7 had autonomic neuropathy. A penile sympathetic skin response was recorded in 18 men with absent corpus cavernosum electromyography.

CONCLUSIONS

Due to false-negative results on corpus cavernosum electromyography and penile sympathetic skin response testing evoked cavernous activity seems more reliable for determining autonomic involvement in the pathophysiology of erectile dysfunction.

Pudendal nerve conduction to evaluate organic erectile dysfunction

OBJECTIVE

This study aimed to evaluate the value of testing pudendal nerve conduction in men with erectile dysfunction.

DESIGN

This open prospective study was conducted on 150 men with documented erectile dysfunction of at least 6 mo of duration, all of whom underwent pudendal nerve conduction by the same investigator.

RESULTS

Only patients with erectile dysfunction and low back pain (n = 9) showed statistically significant prolonged pathologic pudendal nerve conduction latency of 43.1 msec/div (SD +/- 11.3 msec/div, P < 0.05). There were no correlations between the pudendal nerve conduction latency in patients suffering from erectile dysfunction associated with diabetes mellitus, local trauma, pelvic surgery, or antihypertensive drugs.

CONCLUSIONS

Pudendal nerve conduction may contribute valuable information to the evaluation of patients with erectile dysfunction caused by neurologic deficits as manifested by low back pain.

Quantitative sensory and autonomic testing in male diabetic patients with erectile dysfunction

OBJECTIVE

To correlate abnormalities of nerve fibres in the lower limbs with erectile dysfunction in male diabetic patients, using a range of quantitative sensory and autonomic function tests.

PATIENTS AND METHODS

The study included 68 male diabetic patients with symptomatic erectile dysfunction and 11 matched diabetics without erectile dysfunction; none had clinical evidence of peripheral vascular disease or psychological disorder. Patients were evaluated with a symptom questionnaire based on the Michigan Neuropathy Screening Instrument questionnaire and examined clinically. Sural and peroneal nerve-conduction studies, and quantitative sensory and autonomic tests (vibration, thermal, light-touch thresholds, sensory and autonomic cutaneous axon-reflexes) were used to detect nerve abnormalities in the lower limbs, which were correlated with erectile dysfunction.

RESULTS

Symptoms of neuropathy were more common in the group with male erectile dysfunction (MED), but statistically significant only for neuropathic pain (53% MED, 18% nonMED, P<0.05, chi-square test) and gastroparesis (44% MED, 0% nonMED, P<0.05). Tests of unmyelinated afferents (warming perception and capsaicin-induced sensory axon-reflex vasodilatation) were most often abnormal, sometimes with no other abnormalities on tests or neurological examination. However, abnormality of warm perception was not significantly different between groups (81% MED, 70% nonMED), suggesting that it is a poorer discriminant than abnormal sensory axon-reflex vasodilatation (89% MED, 22% nonMED, P<0.001). The only other significant test difference was decreased sural nerve action potential (70% MED, 22% non-MED, P<0.01).

CONCLUSIONS

There appeared to be preferential involvement of unmyelinated sensory fibres that mediate axon-reflex vasodilatation in the limbs of diabetic patients with erectile dysfunction. This test appears to be a helpful indicator of neurological involvement in erectile dysfunction, and may be used to monitor the effect of new treatments.

Sacral reflexes: physiology and clinical application

Sacral reflexes consist of motor responses in the pelvic floor and sphincter muscles evoked by stimulation of sensory receptors in pelvic skin, anus, rectum, or pelvic viscera. These responses may be elicited by physical or electrical stimuli. They have been used in research studies of the pathophysiology of pelvic floor and anorectal disorders and many have been recommended for diagnostic use. These reflexes are described and discussed in this review. More rigorous evaluation of their value in the clinical assessment and care of patients with pelvic floor and sphincter disorders is required. Currently direct comparisons of the value of particular responses are generally not available, and few of these reflexes have proven validity for use in clinical diagnosis.

[Penile neuropathy: clinical and electrophysiologic study. Report of 186 cases]

Penile neuropathy is a common disease due to lesion of the sensory branch of the pudendal nerve, ie, the dorsal nerve of the penis. Sexual disorders (deterioration of erection) and sensory signs (hypoesthesia or paresthesia of the penis) are noted in patients with penile neuropathy. Electrophysiological recordings help guide the diagnosis (reduction of the sensory velocity of the dorsal nerve of the penis). Many etiologies can be found (traumatic, toxic, compressive), but the most common lesion is neuropathy related to diabetes.

Cerebral evoked potentials after stimulation of the posterior urethra in man

Cerebral evoked potentials (EPs) were recorded in 25 neurologically normal subjects aged 22-73 years (mean 44.0) after stimulation of the posterior urethra (PU) and the pudendal nerve. After maximal PU stimulation 2 different configurations of the potential were found. In 12 cases a simple bi-triphasic wave form was recorded while in 12 cases there was a bifid form of the first negative wave. In 1 case identical EPs were recorded after PU and pudendal nerve stimulation. It was concluded that (1) PU stimulation excites fibres in the pudendal nerve at higher stimulation strength, resulting in a bifid wave form of the cerebral evoked potential in some individuals, (2) the most prominent negative peak, N1, with a latency of 102.1 +/- 13.2 msec, is the most reproducible part of the PU-evoked potential, (3) the N1 is probably transmitted through A delta fibres localized in the pelvic nerves, (4) there are differences between individuals concerning pudendal and pelvic nerve involvement in afferent innervation of the urethra.

A neurophysiological study of patients undergoing radical prostatectomy

24 men suffering from localized prostatic cancer undergoing radical retropubic nerve-sparing prostatectomy were investigated by the following electrophysiological methods: Bulbocavernosus reflexes elicited from the penile skin or the posterior urethra, sensory thresholds in the posterior urethra, cerebral evoked potentials after stimulation of the pudendal nerve or the posterior urethra. 15 men were examined 4-33 months postoperatively only, 5 men were examined only preoperatively and 4 men were examined both pre- and postoperatively. 10 men suffering from minor problems due to benign prostatic hyperplasia served as controls. In patients with localized cancer of the prostate, the findings did not differ from those in the control group. In the operated group the findings were pathological in a large proportion of the patients, indicating injuries both to nervous pathways running through the pelvic nerve plexus and in the pudendal nerve. The conclusions were: Localized cancer of the prostate has minimal or no risk at all of impaired functioning in the pelvic nervous pathways. Radical retropubic prostatectomy may in some cases be undertaken without any objective evidence of injury to these nervous pathways, but is often followed by findings indicating such injury. The dorsal nerve of the penis may be affected by the operation. Transcranial stimulation of the motor cortex is a useful method in the evaluation of prolonged or absent bulbocavernosus reflexes.

Lack of relationship of conus reflexes to bladder function after spinal cord injury

A series of 20 patients with acute complete suprasacral cord lesions underwent serial urodynamic assessment of vesicourethral function and serial measurement of sacral reflex latency times (SRL) and reflex threshold throughout a follow-up period of 42 to 83 weeks (mean 50). No correlation was found between any pattern of SRL latencies or reflex thresholds and subsequent bladder behaviour. The reproducibility of sacral reflex latencies was found to be poor (mean variation of serial measurements from initial reading 21%) and could not be explained on the basis of "dynamic" neurological recovery. Studies using the bladder as a stimulus site were unreliable. The value of SRL studies in detecting subtle neurophysiological changes is discussed.

The value of testing for unmyelinated fibre, sensory neuropathy in diabetic impotence

Measurement of thermal thresholds provides a means of assessing neurological deficit and in particular of recognising a neuropathic process affecting unmyelinated and small myelinated fibres of the peripheral nerve. These groups of fibres cannot be tested by nerve conduction studies but are particularly susceptible to disease in diabetes. Thresholds for thermal sensation on the sole of the foot were measured in 33 men presenting with erectile dysfunction. All 15 men with erectile dysfunction, which had been considered on clinical grounds to be neuropathic, had abnormal thermal thresholds. Diabetics with non-neuropathic erectile dysfunction had normal results. Whereas tests of unmyelinated sensory fibre function were abnormal in all those with neuropathic erectile dysfunction, electrophysiological measurement of the bulbocavernosus reflex was normal in five of nine men with diabetic neuropathic impotence.