Botulinum toxin urethral sphincter injection to restore bladder emptying in men and women with voiding dysfunction

PURPOSE: Botulinum toxin injection into the external urinary sphincter in spinal cord injured men with detrusor-sphincter dyssynergia has been reported. We expand the clinical use of botulinum toxin for a variety of bladder outlet obstructions and to decrease outlet resistance in patients with acontractile detrusor but who wish to void by the Valsalva maneuver. MATERIALS AND METHODS: Prospective treatment was performed for voiding dysfunction in 8 men and 13 women 34 to 74 years old. The reasons for voiding dysfunction included neurogenic detrusor-sphincter dyssynergia in 12 cases, pelvic floor spasticity in 8 and acontractile detrusor in 1 patient with multiple sclerosis who wished to void by the Valsalva maneuver. Using a rigid cystoscope and a collagen injection needle, a total of 80 to 100 units of botulinum A toxin (Botox) were injected into the external sphincter at the 3, 6, 9 and 12 o'clock positions. RESULTS: Preoperatively 19 of 21 patients were on indwelling or intermittent catheterization. After botulinum A injection all but 1 patient were able to void without catheterization. No acute complications, such as general paralysis or respiratory depression, occurred and none of the patients had dribbling or stress urinary incontinence. Postoperative post-void residual decreased by 71% and voiding pressures decreased on average 38%. Of the 21 patients 14 (67%) reported significant subjective improvement in voiding. Followup ranges from 3 to 16 months, with a maximum of 3 botulinum A injections in some patients. CONCLUSIONS: Urethral sphincter botulinum injection should be considered for complex voiding dysfunction. Encouraging improvement without complications were seen in most of our patients. We have expanded the use of botulinum toxin to treat pelvic floor spasticity and also women.     

Botulinum toxin in the management of lower urinary tract dysfunction: contemporary update

PURPOSE OF REVIEW: To review the most recent experience concerning the application of botulinum toxin in the human lower urinary tract. RECENT FINDINGS: Botulinum toxin was initially applied in the bladder of patients with spinal neurogenic detrusor overactivity and urinary incontinence, or in the urethra in cases of detrusor external sphincter dyssynergia. A large multicentric European study fully confirmed the initial expectancy in the former condition. In addition, the application of botulinum toxin was extended to the treatment of other urological disorders including non-neurogenic detrusor overactivity, non-relaxing urethral sphincter and detrusor underactivity. Interesting reports on the injection of botulinum toxin into the prostate of patients with benign prostatic hyperplasia are also reviewed. SUMMARY: Bladder injection of botulinum toxin is not yet an approved treatment for lower urinary tract dysfunction. Nevertheless, available data suggest that in the near future the toxin will become a standard therapeutic option in incontinent patients with neurogenic and non-neurogenic forms of overactive bladder, who do not respond to or do not tolerate anticholinergic medication. In addition, it might be expected that urethral botulinum toxin injections improve bladder emptying in patients with dysfunctional voiding problems besides detrusor external sphincter dyssynergia.     

Botulinum A toxin treatment of urethral sphincter pseudodyssynergia in patients with cerebrovascular accidents or intracranial lesions

PURPOSE: Detrusor overactivity and urethral sphincter pseudodyssynergia may develop during recovery from cerebrovascular accidents or intracranial lesions, resulting in difficulty in urination, a large amount of residual urine, and recurrent urinary tract infection. This study evaluated the effectiveness of urethral injection of botulinum A toxin in treating these patients. METHODS: Twenty-one patients with chronic cerebrovascular accidents or intracranial lesions and difficult urination were enrolled. Patients participating in the study elected to receive either 100 units of botulinum A toxin (n = 11) or served as medically treated controls (n = 10). The urodynamic parameters and voiding efficiency after treatment were compared between the 2 groups. RESULTS: An excellent result was obtained in 6 patients and an improved result in 4 patients, resulting in an overall success rate of 91% in the study group. Four patients with frank urinary retention before treatment resumed spontaneous voiding. The maximal effects of botulinum A toxin appeared about 2 weeks after treatment. The voiding pressure decreased (57.8 +/- 35.2 vs. 33.8 +/- 16.9 cm H2O, p = 0.005) and the maximal flow rate increased (7.2 +/- 5.9 vs. 10.3 +/- 5.2 ml/s, p = 0.005) significantly. In the control group, 4 patients (40%) had spontaneous voiding 6 months after medical treatment, whereas 6 patients remained unchanged requiring an indwelling Foley catheter (n = 2) or clean intermittent catheterization (n = 4). The symptom score and the quality of life index showed significantly greater improvement in the study group than in the control group. CONCLUSION: This study demonstrates that urethral injection of botulinum A toxin is effective and without adverse effects in the treatment of patients with urethral sphincter pseudodyssynergia after cerebrovascular accidents or the development of intracranial lesions.     

Refractoriness of urethral striated sphincter during voiding: studies with afferent pudendal reflex arc stimulation in male subjects

To assess the excitability of the striated sphincter under normal and abnormal conditions, electrostimulation of the periurethral striated sphincter via the dorsal nerve of the penis was done with the patient at rest and during voiding. Monitoring of simultaneous intravesical and intramembranous urethral pressures, and electromyographic responses of the striated sphincter was performed under fluoroscopic guidance in 14 male subjects. The urethral striated sphincter attained a state of relative refractoriness during detrusor contraction (voiding phase) and greater amounts of afferent stimulation were required to elicit sphincter contractile activity compared to the amounts required during resting states. Under conditions of a hyperactive detrusor with synergic voiding, the amounts of stimulation required to elicit striated sphincter responses were higher than those required in normal subjects. On the other hand, under conditions of striated sphincter dyssynergia, minute amounts of afferent stimulation were enough to produce sphincter contraction during voiding.     

Role of male pelvic floor muscles and anterior fibromuscular stroma in males on α1‐blocker treatment: A magnetic resonance imaging study

Dynamic motion of the pelvic floor muscles during voiding was analyzed using real‐time magnetic resonance imaging. To evaluate the contraction of the pelvic floor muscles, striated urethral sphincter distance, levator ani muscle thickness and anterior fibromuscular stroma distance were measured. The percent contraction of the striated urethral sphincter from before voiding to just before initiation of voiding was 14% in the normal group and 5% in the voiding dysfunction group. The percent contraction of the anterior fibromuscular stroma from before voiding to just before initiation of voiding was 11% in the normal group and 1% in the voiding dysfunction group; the percent contraction of the muscles was significantly greater in the normal group (P < 0.05). Striated urethral sphincter and anterior fibromuscular stroma contraction at initiation of voiding open the bladder neck and urethra. This plays an important role in the smooth initiation of voiding.     

Botulinum toxin for the treatment of lower urinary tract symptoms: a review

AIMS: To review the available literature on the application of botulinum toxin in the urinary tract, with particular reference to its use in treating detrusor overactivity (DO). METHODS: Botulinum toxin, overactive bladder (OAB), detrusor instability, DO, detrusor sphincter dyssynergia (DSD), and lower urinary tract dysfunction were used on Medline Services as a source of articles for the review process. RESULTS: DO poses a significant burden on patients and their quality of life. Traditionally patients have been treated with anti-cholinergic drugs if symptomatic, however, a significant number find this treatment either ineffective or intolerable due to side effects. Recent developments in this field have instigated new treatment options, including botulinum toxin, for patients' refractory to first line medication. Botulinum toxin, one of the most poisonous substances known to man, is a neurotoxin produced by the bacterium Clostridium botulinum. Botulinum toxin injections into the external urethral sphincter to treat detrusor sphincter dyssynergia has been successfully used for some years but recently its use has expanded to include voiding dysfunction. Intradetrusal injections of botulinum toxin into patients with detrusor overactivity and symptoms of the overactive bladder have resulted in significant increases in mean maximum cystometric capacity and detrusor compliance with a reduction in mean maximum detrusor pressures. Subjective and objective assessments in these patients has shown significant improvements that last for 9-12 months. Repeated injections have had the same sustained benefits. CONCLUSIONS: Application of botulinum toxin in the lower urinary tract has produced promising results in treating lower urinary tract dysfunction, which needs further evaluation with randomised, placebo-controlled trials.     

Is it reasonable to treat refractory voiding dysfunction in children with botulinum-A toxin?

PURPOSE: We present our results with botulinum-A toxin transperineal pelvic floor/external sphincter injection combined with behavioral and biofeedback reeducation in children with voiding dysfunction who had been resistant to previously applied therapies. MATERIAL AND METHODS: Eight boys and 12 girls between 7 and 12 years old (mean age 9) with recurrent urinary tract infection, an interrupted or fractional voiding pattern and high post-void residual urine in whom behavioral, short biofeedback and alpha-blocker therapies had failed were included in the study. They were treated with botulinum-A toxin at a dose of 50 to 100 U. Botulinum-A toxin was injected transperineally into the pelvic floor and/or external sphincter in all patients. In boys the sphincter was localized endoscopically before injection (endoscopically assisted transperineal approach). Behavioral and biofeedback reeducation started 15 days after injection. RESULTS: Followup was between 9 and 14 months. All patients were without urinary tract infection and fever, while 5 were still on chemoprophylaxis. Six months after treatment residual urine decreased in 17 of 20 patients by 0 to 130 ml (mean +/- SD 45.75 +/- 32.17 ml, t = 6.360, p <0.001). Nine patients reestablished a normal voiding curve and 8 showed improvement. Three did not manifest any significant improvement. In 1 girl transitory incontinence resolved spontaneously within 48 hours. There were no other complications. CONCLUSIONS: The effect of botulinum is transitory. However, it can break the circle of detrusor-sphincter dyssynergia and the period when it is sustained can be used for retraining the patient in normal voiding. At this moment botulinum-A toxin is one of last options in refractory cases of voiding dysfunction.     

The bladder in boys with posterior urethral valves: a urodynamic assessment.

Urodynamic evaluation was performed on 8 of 62 boys (13 per cent) with persistent voiding difficulties after fulguration of posterior urethral valves. All had varying degrees of incontinence when evaluated. The striated muscle component of the external urethral sphincter was intact in each child. Five different types of bladder function were noted in the 8 children. Three boys had had a prior Y-V plasty of the bladder neck to improve upper and lower urinary tract emptying, which may have contributed to the subsequent incontinence. One additional boy had significant bladder neck obstruction requiring a unilateral bladder neck incision to improve voiding. Appropriate treatment plans were instituted based on the urodynamic findings of the bladder, bladder neck and external sphincter areas, and 6 of the 8 children are now completely continent.     

Effectiveness of urethral injection of botulinum A toxin in the treatment of voiding dysfunction after radical hysterectomy

OBJECTIVE: After radical hysterectomy for cervical cancer patients may have difficulty in urination due to detrusor underactivity and a non-relaxing urethral sphincter. This study evaluated the effectiveness of urethral injection of botulinum A toxin in treating voiding dysfunction in these patients. METHODS: Thirty patients with difficult urination after radical hysterectomy due to cervical cancer were enrolled to receive urethral injection of 100 units of botulinum A toxin (n=20) or medical treatment as controls (n=10). The clinical results and urodynamic parameters at baseline and after treatment were compared in the study group, and the quality of life (QOL) index was compared between the study and control groups. RESULTS: After urethral injection of botulinum A toxin, 8 patients had excellent results (40%) and 8 had improved results (40%) in the study group. Both voiding pressure (115.2+/-63.7 vs. 90.2+/-49.5 ml, p=0.025) and post-void residual volume (330.9+/-124.9 vs. 183.9+/-183.4 ml, p=0.011) improved significantly after treatment. The obstructive symptom score was significantly reduced (17.5+/-4.7 vs. 5.7+/-2.3 points, p=0.000) and the QOL index also improved (4.5+/-2.7 vs. 2.3+/-2.3 points, p=0.000) after treatment. The success rate was 80% in the study group. There were no significant changes in obstructive symptom scores or the QOL index in the control group. The maximal effect appeared about 1 week after treatment. The duration of the therapeutic effect ranged from 3 to 9 months. Mild stress urinary incontinence and nocturnal enuresis were noted in 7 patients (35%). CONCLUSION: Urethral injection of botulinum A toxin can be effectively used to treat patients with detrusor underactivity and non-relaxing urethral sphincter after radical hysterectomy with few adverse effects.     

Botulinum A toxin urethral injection for the treatment of lower urinary tract dysfunction

PURPOSE: This study investigates the effectiveness of botulinum A toxin in the treatment of various types of lower urinary tract dysfunction and determines the predictive factors for a successful outcome. MATERIALS AND METHODS: A total of 103 patients with chronic urinary retention (45) or severely difficult urination (58) received urethral injection of botulinum A toxin. The dose was 50 units in 48 patients and 100 units in 55. Clinical effects and urodynamic parameters were compared at baseline and after treatment. RESULTS: The 48 men and 55 women (age range 14 to 86 years) had various types of lower urinary tract dysfunction including detrusor sphincter dyssynergia in 29, dysfunctional voiding in 20, nonrelaxing urethral sphincter in 19, cauda equina lesion in 8, peripheral neuropathy in 14 and idiopathic detrusor underactivity in 13. A total of 40 (39%) patients had an excellent result and 47 (46%) had significant improvement as assessed by the patients. The total success rate was 84.5%. Among these patients mean maximum voiding pressure decreased significantly (62 +/- 40 vs 43 +/- 31 cm H2O, p = 0.000), as did maximal urethral closure pressure (65 +/- 36 vs 48 +/- 31 cm H2O, p = 0.000) and post-void residual (226 +/- 165 vs 89 +/- 112 ml, p = 0.000) at 2 to 4 weeks after treatment. Among 45 patients with urinary retention the indwelling catheters were removed or clean intermittent catheterization was discontinued in 39 (87%). CONCLUSIONS: Botulinum A toxin urethral injections at doses of 50 or 100 units were effective in decreasing urethral sphincter resistance in patients with various types of lower urinary tract dysfunction.     

Botulinum toxin as a new therapy option for voiding disorders: current state of the art

Botulinum toxin is a presynaptic neuromuscular blocking agent inducing selective and reversible muscle weakness up to several months when injected intramuscularly in minute quantities. Different medical disciplines have discovered the toxin to treat mainly muscular hypercontraction. In urology, indications for botulinum-A toxin have been neurogenic detrusor overactivity, detrusor-sphincter dyssynergia, motor and sensory urge and, more recently, chronic prostatic pain. The available literature was reviewed using Medline Services. The keywords "botulinum-A toxin", "detrusor-sphincter dyssynergia", "neurogenic bladder", "spinal cord injury", "denervation", "chronic prostatic pain", "chronic urinary retention" were used to obtain references. A toxin injection is effective to treat detrusor-sphincter dyssynergia when injected either transurethrally or transperineally. After treatment, external urethral sphincter pressure, voiding pressure and post-void residual volume decreased. The effect lasts between 2 to 9 months depending on the number of injections. Best indications seem to be multiple sclerosis and incomplete spinal cord injury patients suffering from neurogenic detrusor overactivity and detrusor-sphincter dyssynergia. According to the previous results, the use of botulinum-A toxin injections into the external urethral sphincter has been extended to a variety of bladder obstructions and to decrease outlet resistance in patients with acontractile detrusor. In cases of successful treatment, spontaneous voiding re-occurs and catheterization can be resumed. Injections of the toxin into the external urethral sphincter also seem to have a beneficial effect on chronic prostatic pain, presumably by reducing hypertonicity and hyperactivity of the external urethral sphincter. Injections of botulinum-A toxin into the detrusor muscle has first been tested to treat neurogenic detrusor activity in spinal cord injured patients and in myelomeningocele children. Long lasting (mean 9 months) detrusor relaxation occurs after injection of usually 300 units of Botox). Continence is restored in about 95% of the patients and anticholinergic drugs can be markedly reduced or even stopped. Excellent results of botulinum-A toxin injections into the detrusor in neurogenic detrusor overactivity have lead to an expansion of this treatment to incontinence due to idiopathic detrusor overactivity. Although preliminary results are promising, adequate dosage of the toxin required for this indication is not yet known. In conclusion, it appears that botulinum toxin injection into either the external urethral sphincter or the detrusor offers new promising treatment options for many different urological dysfunctions. However, large controlled trials are absolutely required to establish the role of botulinum-A toxin injections in the fields of urology and neurourology on evidence based medicine.     

Influences of external urethral sphincter relaxation induced by alpha-bungarotoxin, a neuromuscular junction blocking agent, on voiding dysfunction in the rat with spinal cord injury

OBJECTIVES: To determine whether external urethral sphincter (EUS) relaxation induced by alpha-bungarotoxin, a highly selective neuromuscular junction blocking agent, could ameliorate voiding dysfunction after spinal cord injury (SCI) in rats. METHODS: The effects of intravenous alpha-bungarotoxin (333 microg/kg) were evaluated during cystometry in decerebrate, unanesthetized female Sprague-Dawley rats (250 to 300 g) with spinal cords chronically transected at T7-9 (n = 7) or with normal spinal cords (NSC) (n = 7). Parameters measured included voided volume (VV), residual volume (RV), volume threshold for inducing micturition (VT), voiding efficiency (VE), micturition pressure (MP), pressure threshold for inducing micturition (PT), bladder contraction duration (BCD), and compliance (CP). RESULTS: In SCI rats, treatment with alpha-bungarotoxin improved voiding. The toxin increased VE (31%) and reduced RV (42%), MP (52%), BCD (14%), and VT (31%). VV, PT, and CP were not altered. In NSC rats, alpha-bungarotoxin decreased VE (23%), increased RV (63%), and decreased MP (36%), VV (38%), and VT (20%) but did not change BCD and CP. CONCLUSIONS: The results of our study demonstrated that alpha-bungarotoxin improved voiding in SCI rats by reducing urethral outlet resistance. However, in NSC rats, the toxin reduced voiding, probably by suppressing high-frequency phasic sphincter activity, necessary for efficient urine elimination in normal animals. The present results provide further support for the view that drugs that depress striated muscle activity can be useful in the treatment of voiding dysfunction after SCI.     

The urethral syndrome

The term urethral syndrome reflects irritation in the external urethral (striated) sphincter. The cause of this condition may be as much poor voiding habits as it is infection or trauma. Treatment principles therefore involve retraining the voiding mechanism, as well as the judicious use of antibiotics, skeletal muscle relaxants, and an alpha-blocker. Neurostimulation has been used successfully to relieve symptoms in occasional refractory cases.     

Botulinumtoxin-A-Injektion bei therapierefraktärer Giggle-Inkontinenz

A 20-year-old woman reported about giggle incontinence despite antimuscarinic therapy. Therefore we injected botulinum toxin A into the detrusor muscle. The effect of botulinum toxin A appeared about 1 week after injection and no more leakage was observed even during vigorous laughter. A control uroflowmetry showed a good voiding rate without any residual volume. Botulinum toxin A might be an alternative for patients with giggle incontinence after unsuccessful antimuscarinic treatment.     

Electromyographic study of the striated urethral sphincter by using the bulbocavernosus reflex: study of the normal voluntary voiding and the involuntary sphincter relaxation

PURPOSE: The aim of this study was to investigate the sacral reflex activity at the striated urethral sphincter relaxation by evoking the potential of the bulbocavernosus reflex (BCR). METHODS: 17 normal male subjects were investigated. BCR was elicited by electrical stimulation of dorsal nerve of the penis, and the evoked potential of the BCR (BCR-EP) was recorded by a concentric needle electrode at the periurethral striated muscle. In normal subjects BCR was performed at rest and during voluntary voiding. In 8 of the normal subjects electrical stimulation was increased gradually during voluntary voiding, and changes of BCR-EP were studied. 3 male patients with neurogenic bladder suffering from urinary incontinence caused by involuntary sphincter relaxation (IVSR) were also investigated. In these patients with neurogenic bladder, BCR was performed at rest and during voluntary voiding as well as during involuntary voiding. RESULTS: In the normal subjects stable BCR-EP was elicited at rest and disappeared during voluntary voiding. But a gradually increased larger stimulation clearly demonstrated BCR-EP during voluntary voiding. In 3 patients with neurogenic bladder, stable ECR-EP was elicited at rest. During involuntary voiding caused by IVSR obvious BCR-EP was also elicited, but its amplitude was slightly less than the amplitude of BCR-EP at rest. During voluntary voiding in 2 of the 3 patients BCR-EP was recognized but the amplitude was much less, and in the third patient BCR-EP could not be recognized. CONCLUSION: BCR-EP was suppressed during voluntary voiding in normal subjects, but insufficiently suppressed in the patients with neurogenic bladder. In these patients BCR-EP during voluntary voiding was suppressed more distinctly than BCR-EP during involuntary voiding due to IVSR. In urodynamic study, the detrusor contraction and the sphincter relaxation were common phenomenon in both voluntary voiding and involuntary voiding, but the difference in the degree of the BCR suppression depended on whether micturition was voluntary or involuntary. It was suggested that the measurement of BCR-EP could distinguish involuntary voiding caused by pathological urethral sphincter relaxation from voluntary voiding.     

Female urethral syndrome: Clinical and urodynamic perspectives

Eighteen women with the urethral syndrome were studied urodynamically with synchronous video-pressure flow studies and electromyography of the external urethral sphincter (EUS). When compared with an age and sex matched control group, the most striking finding was a significantly higher than normal maximum urethral closure pressure. Abnormal and low urinary flow rates, instability of the intraurethral pressure at rest, incomplete funnelling of the bladder neck, and distal urethral narrowing during voiding constitute other typical urodynamic findings in the female urethral syndrome. Detrusor-striated sphincter dyssynergia or primary striated sphincter spasm was not observed. Even though striated E US spasticity cannot be excluded as a cause of this syndrome in some patients, an autonomically mediated spasm of the smooth muscle sphincter seems plausible to explain both our urodynamic findings and a favorable response of 4 patients treated with alpha-blocking agents.     

A prospective study of botulinum toxin for internal anal sphincter hypertonicity in children with Hirschsprung's disease

BACKGROUND: Internal anal sphincter hypertonicity with nonrelaxation can cause persistent constipation and obstructive symptoms in children after surgery for Hirschsprung's disease. Intractable symptoms traditionally have been treated with anal myectomy, which may be ineffective or complicated by long-term incontinence. The authors evaluated prospectively the use of intrasphincteric botulinum toxin for these patients. METHODS: Eighteen children were studied (age 1 to 13; median, 4 years). Botulinum toxin was injected (total dose 15 to 60 U) into 4 quadrants of the sphincter. Resting sphincter pressure was measured in 14 patients before and after injection. Ten have had 1 to 5 additional injections (total dose, 30 to 60 U per injection). RESULTS: Four patients had no improvement in bowel function, 2 had improvement for less than 1 month, 7 had improvement for 1 to 6 months, and 5 had improvement more than 6 months. Nine of those with symptomatic improvement longer than 1 month had pressures measured, with a documented decrease in 8. Five with no significant clinical improvement had pressure measurements, with a decrease in 3. There were no adverse effects associated with botulinum toxin injection. Four children had new encopresis postinjection, which was mild and resolved in each case. CONCLUSIONS: Intrasphincteric botulinum toxin is a safe and less-invasive alternative to myectomy for symptomatic internal sphincter hypertonicity. Persistent symptoms, despite a fall in sphincter pressure, suggest a nonsphincteric etiology. Repeat injections often are necessary for recurrent symptoms.     

Long‐term outcome of the use of botulinum toxin injection for functional anal pain

Aim Anal pain may occur in the absence of demonstrable anal pathology. Spasm of the sphincter muscles has been suggested as a cause in some patients. We aimed to assess the effectiveness of injection of botulinum toxin in treating this condition. Method Patients who had injection of botulinum toxin over a 3‐year period were identified retrospectively. Patients were excluded if anal fissure or other organic pathology was found to account for their symptoms on examination under anaesthetic. Long‐term outcome was assessed at a minimum 3‐year post‐procedure telephone follow up. Results Fourteen (eight male) patients were identified, of median age 50 years. Botulinum toxin (20–200 u) was injected into the internal sphincter. Seven of the 14 patients reported significant improvement in symptoms at 3 months. Seven were available for a structured telephone review at a median of 59 (42–68) months. The four patients who had benefited from the injection had remained asymptomatic. Conclusion Injection of botulinum toxin into the internal anal sphincter has a role in alleviating symptoms in a small proportion of patients with functional anal pain.     

A study of the continence mechanism of the external urethral sphincter with identification of the voluntary urinary inhibition reflex

PURPOSE: The role of the external urethral sphincter in the opposition and interruption of the act of voiding was investigated. MATERIALS AND METHODS: The study included 7 men and 5 women with a mean age plus or minus standard deviation of 38.6 +/- 11.2 years. The bladder was filled with saline up to the urge sensation. Detrusor and posterior urethral pressures were recorded before and upon resisting the reflex detrusor contraction, and upon interrupting voiding by voluntary external urethral sphincter contraction. The test was repeated by interrupting the urinary stream with external urethral sphincter electrostimulation. The electromyography response of the internal urethral sphincter to the suppression and interruption of voiding was documented before and after internal urethral sphincter anesthetization. RESULTS: Suppression of the reflex detrusor contraction as well as of urinary stream interruption by external urethral sphincter contraction voluntarily or by electrostimulation resulted in a significant detrusor pressure decrease (p <0.01) and urethral pressure increase (p <0.001). Internal urethral sphincter electromyography activity, which normally disappears during voiding, was still present. After internalurethral sphincter anesthetization subjects suppressed the reflex detrusor contraction by voluntary external urethral sphincter contraction for a mean of 62.6 +/- 9.6 seconds, after which involuntary voiding occurred. The internal urethral sphincter showed no electromyography activity. CONCLUSIONS: The external urethral sphincter induces continence by preventing internal urethral sphincter relaxation at the detrusor contraction, which is suggested to be reflex in nature and is called the voluntary urinary inhibition reflex, and by mechanically compressing the urethra. Contraction of the external urethral sphincter, which is a striated muscle, mechanically occludes the urethra for a few seconds, by which time the detrusor has relaxed as an effect of the voluntary inhibition reflex.