Urinary retention in women: its causes and management

Transcription

1 Original Article URINARY RETENTION IN WOMEN KAVIA et al. Urinary retention in women is a diagnostic and therapeutic challenge to urologists and to all involved in the treatment of the condition. The patients referred to a single institution with this condition over a 4-year period were audited and the data are presented. The importance of Fowler s syndrome is described, as is the value of sacral nerve stimulation in this condition. In another paper, authors from France present evidence of occult dysautonomia in Fowler s syndrome. Urinary retention in women: its causes and management RAJESH B.C. KAVIA, SOUMENDRA N. DATTA, RANAN DASGUPTA, SOHIER ELNEIL and CLARE J. FOWLER Department of Uro-Neurology, National Hospital for Neurology and Neurosurgery, London, UK Accepted for publication 25 August 2005 OBJECTIVE To report the experience of the last 4 years from a centre to which women with voiding difficulties and urinary retention were referred nationally, describing what investigations were helpful in making a diagnosis and the management strategies used the patients with known other causes of voiding dysfunction (66.2 cmh 2 O) was 35.3 cmh 2 O (P < 0.05). In patients with complete retention there was a significant difference in sphincter volume between those who were EMG-positive (2.14 ml) or EMGnegative (1.64 ml) (P < 0.05). CONCLUSION PATIENTS AND METHODS Women with voiding difficulties and urinary retention remain a diagnostic and management challenge, and those with no anatomical or neurological basis for their symptoms may be dismissed, assuming that their retention has a psychogenic basis. The finding of an electromyographic (EMG) abnormality of the striated urethral sphincter explaining their disorder (Fowler s syndrome) has led to the referral of women for consideration of that diagnosis. Thus we audited the referrals to the centre over a 4-year period of such women. RESULTS In all, 247 women (mean age 35 years) with complete (42%) or partial retention (58%) were referred; 175 (71%) had urethral pressure profilometry, 141 (57%) had a transvaginal ultrasonographic measurement of the sphincter volume, and 95 (39%) had sphincter EMG. The mean maximum urethral closure pressure difference between patients with an EMG abnormality (101.5 cmh 2 O) and These investigations helped to classify the cause of retention in two-thirds of cases. The commonest diagnosis was Fowler s syndrome, in which sacral nerve stimulation is the only intervention that restores voiding. KEYWORDS urinary retention, women, Fowler s syndrome, sacral nerve stimulation INTRODUCTION Urinary retention in women is not a common complaint, but those cases that do occur may present considerable management problems to the urologist. Otherwise fit young women with a complete inability to void and an intolerance of intermittent selfcatheterization reasonably demand an alternative to a long-term indwelling suprapubic catheter. Urological reviews list various pathologies as causes of retention, some anatomical and some functional. Mechanical obstruction can be caused by tumours, urethral diverticula, bladder neck 2006 BJU INTERNATIONAL 97, doi: /j x x 281

2 KAVIA ET AL. stenosis, bladder calculi, and rarely urethral strictures or pelvic organ prolapse. Antiincontinence procedures are also known to cause some cases of urinary retention [1,2]. Non-structural or functional causes of voiding difficulty are most commonly caused by neurological disorders, although those neurological lesions involving the spinal cord usually result in a combination of detrusor overactivity (DO) and detrusor-sphincter dyssynergia (DSD). In that situation, DO usually dominates the clinical picture but sometimes obstructed voiding, incomplete emptying and retention can be major problems. However, a key clinical feature of spinal cord diseases which may cause DO and DSD is that other neurological features are usually present, so that retention is seen in the context of a spastic paraparesis. Likewise, if the bladder dysfunction is due to sacral root damage, other clinical features of a cauda equina deficit will be apparent [3]. Until the latter part of the last century it was taught that those women who had neither an anatomical abnormality nor a diagnosed neurological condition had a psychogenic basis for their retention. However, in 1985 an electromyographic (EMG) abnormality of the striated urethral sphincter was described, which it was hypothesized, impairs urethral relaxation [4,5], and a series of patients was described with a primary disorder of sphincter relaxation, presenting either with obstructed voiding and incomplete retention or complete retention. Many of the young women also had a history or clinical features of polycystic ovaries [6]. Over the last 20 years this condition has since become known as Fowler s syndrome, the term usually being applied in UK clinical practice to a young woman with otherwise unexplained complete urinary retention. The association with polycystic ovaries is by no means invariable but the exclusion of underlying urological or neurological pathology is essential to the diagnosis. A retrospective questionnaire survey showed that the syndrome is characterized by painless urinary retention with a bladder capacity in excess of 1 L, and often difficulty in removing the catheter used for self-catheterization [7]. We report the experience of the last 4 years from a centre to which women with voiding difficulties and urinary retention were referred nationally, describing what Questions What worried you most about your condition? What management was started at local hospital? Was a diagnosis made at local hospital? Was a diagnosis made at NHNN? What treatment options were discussed at NHNN? Was an explanation of your diagnosis given? Did you find this helpful? Were you satisfied with the consultation? If no treatment was available did you feel that the opportunity to discuss your medical complaint worth the journey to the hospital? How many doctors/specialists had you seen prior to visit to Professor Fowler s Clinic? How long did it take you to travel up to the hospital? How far did you travel to attend the clinic? How much did it cost? Were you satisfied with your experience at the NHNN? investigations were helpful in making a diagnosis and the management strategies used. PATIENTS AND METHODS We retrospectively reviewed the clinical features of all women referred to the Department of Uro-Neurology, National Hospital for Neurology and Neurosurgery (NHNN) during the period January 2001 to December 2004 inclusive, with either obstructed voiding and intermittent/partial retention or complete retention. Any women known to have neurological symptoms or signs (particularly in the lower limbs) or suspected of having a structural lesion was excluded for this review. The source of referral, including the speciality of the referring practitioner and the area of country where the patient resided was recorded. An survey was sent to consultant BAUS members asking about the number of women in retention they had seen in a year. A questionnaire was also sent to 50 consecutive patients referred in 2003 asking them to evaluate their opinions before and after referral to our department, about the consultations and diagnostic/prognostic outcomes (Table 1). The laboratory investigations comprised the following: Urethral pressure profilometry (UPP): based on a previous study from this department [8], TABLE 1 Questions from the patientexperience questionnaire the maximum urethral closure pressure (MUCP) measured using a perfusion-catheter technique, was found to be abnormally high in women with a primary abnormality of sphincter relaxation due to abnormal sphincter EMG activity. Although there is no consensus as to control values for the MUCP, our control range is based on work by Edwards and Malvern [9] using the same perfusion-catheter technique, who showed that the MUCP is reproducible when age is considered, and proposed the formula MUCP = (92 patient age in years) cmh 2 O. Sphincter volume (SV) by ultrasonography (US); the same study [8] also showed that when measured with two-dimensional US, the urethral SV (three-dimensional volume calculated using formula for the volume of a cylinder) was significantly larger in women with the EMG abnormality. However, the interobserver variability of this measurement is high, as some subjectivity is involved in defining the proximal and distal boundaries of the sphincter. Sphincter EMG; the concentric needle electrode EMG findings diagnostic of Fowler s syndrome are complex repetitive discharges and decelerating bursts, which when transduced to the audible spectrum, sound like the noises of helicopters and underwater whales, respectively. However, the test is uncomfortable and technically difficult, requiring some EMG expertise, so that in general it was only used in patients with a history suggestive of Fowler s syndrome, a high MUCP and with or with no high SV, and BJU INTERNATIONAL

3 URINARY RETENTION IN WOMEN FIG. 1. The age range of the referred women. 100 Age at Referral FIG. 2. The sources of referrals of the 247 women. 27 (11%) 12 (5%) 9 (4%) Age, years (16%) Urologist Neurologist Gynaecologist Other specialities Unknown 159 (64%) Year of Referral FIG. 3. The map of referrals from the UK, in whom neuromodulation was being strongly considered, or in those who had an equivocal history and high MUCP. Peripheral nerve evaluation (PNE): the traditional approach had been to perform a test procedure for sacral nerve stimulation under local anaesthesia using a temporary stimulating electrode placed in the S3 foramen, and positioned to produce optimal sensory (vaginal/rectal tingling or a sensation of drawing in ) or motor (anal contraction or hallux flexion) responses. The lead is left in place for 4 7 days and the effect on voiding assessed by a diary kept by the patient of measured voids, etc. If there is a positive response (normalization of bladder function or >50% improvement in baseline diary data) the patient is then considered for a permanent lead and implantable pulse generator (IPG, InterStim Therapy, Medtronic Inc, Minneapolis, USA). Sacral nerve stimulation (SNS): Before 2004, the technique for SNS involved a single-stage operation for implanting the stimulating lead, necessitating a deep sacral dissection and insertion of the IPG into the anterior abdominal wall or buttock. The reoperation rate with this method has been high, up to 50%, with complications including loss of efficacy, pain, lead migration and infections [10]. Furthermore, there was a high discontinuation rate after a successful PNE, up to 40% of patients show no clinical benefit with the IPG [11]. In 2000, a new minimally invasive two-stage procedure was devised, using a permanent self-securing tined electrode placed under local anaesthesia, and using fluoroscopic guidance and the patient s sensory response [12,13]. This lead is left in situ for 2 4 weeks and connected to an external stimulator. If the patient improves significantly, the stimulator can then be internalized. We started to use this in 2004, so that the most recent data reflects that practice. The findings of all the laboratory investigations were analysed; and the results of the PNE and the number of patients who progressed to treatment with SNS were reviewed. RESULTS Belfast Of the 247 women seen over the 4 years, 103 (42%) presented with complete retention and 144 (58%) with a combination of obstructed voiding and intermittent/partial retention. In addition to the primary voiding problem, Cardiff Edinburgh Manchester Birmingham Key and Number of referrals Referrals Referrals Referrals Referrals London London (within M25) Referrals Referrals Referrals Referrals Guernsey other complaints included recurrent UTIs, symptoms of an overactive bladder, including frequency, urgency, or urgency incontinence (mostly those with obstructed voiding and intermittent/partial retention) and bowel symptoms of constipation. The mean (range) age of the referred women in retention was 35.0 (12 81) years ((Fig. 1). Most patients were referred by urologists (64%), with neurologists (16%) and gynaecologist (11%) accounting for most of the other referrals (Fig. 2). The patients had seen an average of three specialists previously. Patients travelled from all parts of mainland UK (Fig. 3), some in excess of 400 miles (640 km) BJU INTERNATIONAL 283

4 KAVIA ET AL. In all, 58 consultant BAUS members replied to the survey and from this it was estimated that a mean of one patient/year was seen per consultant, resulting in 630 women/year presenting with unexplained urinary retention. The anonymous patient satisfaction questionnaire (23 respondents) showed that >80% of the women were satisfied with their consultation at NHNN and importantly 60% of the women who were offered no treatment felt that the opportunity to discuss their problem was of great benefit. There were no negative responses received, although 40% of the women did not respond to the question. Cause of retention N (%) Associated with: CIPO* 7 (2.8) with high-dose opiates* 5 (2.0) Detrusor failure 4 (1.6) Pain/structural 4 (1.6) Iatrogenic 3 (1.2) Neurological 3 (1.2) Idiopathic DO 2 (0.8) Diagnosis unknown 79 (32.0) Primary disorder of sphincter relaxation 142 (57.5) *two patients had both CIPO and high-dose opiates; associated with tight colposuspension or tight transvaginal tape; associated with transverse myelitis, multisystem atrophy, or neurological diagnosis under investigation. TABLE 2 Causes of voiding dysfunction Most of the women had been investigated at their local hospital with flow rates and postvoid residual volume, cystometry or cystoscopy. At the NHNN, 175 (71%) had UPP, 141 (57%) had a transvaginal US measurement of the SV and 95 (39%) had sphincter EMG. Only six patients had a sphincter EMG with no MUCP or SV measurement. The EMG findings of the 95 women who had the test showed positive findings of complex repetitive discharges and decelerating bursts in 81; no abnormality was found in 14. The mean (SD) MUCP for patients with voiding dysfunction and the EMG abnormality was high, at (2.9) cmh 2 O, the expected mean for this group based on their mean age being 57 cmh 2 O (P < 0.05). To investigate whether the MUCP is a useful diagnostic test for the primary disorder of sphincter relaxation, we compared the mean MUCP in patients with EMG abnormality and that in patients with known other causes of voiding dysfunction, at 66.2 (5.8) cmh 2 O; the difference was 35.3 cmh2o (P < 0.05). There was no significant difference in MUCP between women with a normal sphincter EMG and positive EMG, which may be explained as only women with a high MUCP tended to have the investigation. The mean SV was 2.05 ml, with no difference between the groups who were EMG-positive, negative or not assessed. However, among those with complete retention, there was a significant difference between those EMG-positive, at 2.14 ml, and EMG-negative, at 1.64 ml (P < 0.05). There was also a significant difference between the EMG-positive group and the group with other diagnoses, at 2.12 (0.07) and 1.88 (0.16) ml, respectively (P < 0.05). FIG. 4. The results of patients entering into the SNS programme., successful PNE;, unsuccessful PNE; W/L, waiting list. PNE (n = 44) N = 24 N = 20 Based on investigations carried out in our department the causes of retention are listed in Table 2. An abnormal EMG in 81 confirmed a diagnosis of the primary disorder of sphincter relaxation and the same diagnosis was also made in 61 women based on a detailed history, MUCP and SV measurement. In women in whom MUCP, SV or EMG were normal the history of association with severe constipation (possibly secondary to chronic idiopathic pseudo-obstruction, CIPO) or and/or high opiate use (pethidine, morphine or tramadol), suggested detrusor dysfunction. An unrecognized neurological diagnosis (one patient in whom a history of transverse myelitis had been overlooked, one who subsequently developed multisystem atrophy and one who developed leg weakness and is still under investigation) was rare. In almost a third of the patients a definitive diagnosis for Single-stage implant (N = 3) 2-staged implant (N = 13) W/L for 2 staged implant (N = 8) 2 staged implant (N = 4) W/L for 2 staged implant (N = 2) N = 3 N = 12 N = 1 N = 3 N = 1 Withdrawn from stimulator program (N = 14) their voiding problems could not be reached, as some had resolution or improvement of symptoms, while others decided that they did not want further investigations. The management of patients is currently limited to clean intermittent selfcatheterization or SNS. Although SNS can restore voiding in women with Fowler s syndrome, it is a resource-intensive procedure requiring several hospital visits and it is unsuitable for those who found the journey to central London difficult, or for noncompliant patients who found keeping diaries difficult. At the NHNN before August 2004 all implants were placed at one operation, subsequently the staged operation was used. Of the 247 women referred over the 4 years, 44 had a PNE (Fig. 4; the test procedure for SNS) and two patients await the procedure. Of the 44 patients, voiding was restored in 24 (55%). Of BJU INTERNATIONAL

5 URINARY RETENTION IN WOMEN the failures, eight (18%) were for technical reasons, including an inability to cannulate the sacral foramen under local anaesthesia; two of the women who had a sensory response to the PNE but did not void, went on to void with the staged SNS procedure. Ten patients are on the waiting list for the staged SNS procedure, and 18 have had permanent SNS implants in the past 4 years (three singlestage procedures and 15 staged operations). DISCUSSION Voiding dysfunction in women remains a difficult condition to manage. Many patients had treatment with α-blockers or urethral dilatation, with little success, and faced the prospect of indefinite, often uncomfortable intermittent catheterization or a permanent drainage procedure (either an indwelling catheter or a surgical procedure). For many of the patients, referral to the NHNN was their last resort for explanation, diagnosis or treatment for their urinary problem. This was often an expensive visit, with costs that included travel, accommodation, child-care, absence from work, etc., plus the cost to those who accompanied the patient, unfamiliar to travel in London. For all these reasons every attempt was made to reach a diagnosis on the day of the outpatient consultation. Sometimes this was possible based on the history alone, but frequently laboratory investigations were required. Table 2 lists our conclusions about the various causes of urinary retention in the 247 women seen over the 4 years. In almost a third no diagnosis could be made for the reasons already given, but in the remainder allocation to a diagnostic category was made, as shown. CIPO is a rare syndrome characterized by chronic intestinal obstruction with no anatomical or mechanical lesion. Although urological problems have been described [14], few reports have focused on this association. Bladder dysfunction has been reported in up to 10 69% of patients with CIPO [15 17]. The exact mechanism of voiding dysfunction is unknown, but urodynamic investigations reveal a hypocontractile detrusor, increased capacity, increased residual volume and decreased bladder sensation [16], and it is presumed that this is due to the same visceral myopathy or neuropathy that affects the bowel. Many can void with the Valsalva manoeuvre and perineal relaxation, but for those unable to do so, options are limited to catheterization or urinary diversion. In many patients the condition is characterized by abdominal pain for which patients may take opiates. Both CIPO and opiate overuse result in severe constipation and a link has been reported between fecal impaction and urinary retention [18]. Five women were on high doses of opiates for the treatment of chronic back pain. A link has been shown with the use of opiates and voiding dysfunction and retention [19]. There is urodynamic evidence that opiates result in decreased bladder sensation and increased residual volume, as well as decreased detrusor contractions [20]. The effect may be doserelated, as shown by the greater risk of postoperative retention with patientcontrolled analgesia than with i.m. opiates [21,22]. Animal studies suggest that the activation of µ-opioid receptors in the periaqueductal grey inhibit detrusor contractions [23]. The voiding dysfunction tends to be reversible with withdrawal of the opiate, but it is often difficult to reduce consumption in those dependent on these drugs. The commonest cause of urinary retention in these young women was a primary disorder of sphincter relaxation (Fowler s syndrome). The full aetiology of this condition remain to be elucidated but it has been hypothesized that the disorder is due to a hormonally sensitive channelopathy [24], which results in a sustained involuntary contraction of the striated urethral sphincter. This in turn has an inhibitory effect on detrusor contractions as well as inhibiting sensations of the desire to void. The rapidity of the effect of neuromodulation, which starts to restore voiding function within 24 h, suggests that this intervention works by reversing the inhibitory effect of the sphincter contraction. The abnormalities of sphincter function, i.e. abnormal EMG activity and high MUCP, are not reversed by neuromodulation [25]. The management of bladder dysfunction, both incontinence and retention, with SNS has classically been with an initial test procedure, followed by permanent implantation. Success rates with this method were reported as 40 68% [26 28] for the PNE and 60% of women voided to completion with a formal implant, and another 14% reported a significant improvement at 18 months. The present results show that two-thirds of patients continue to void without catheterization at a mean follow-up of 5 years [10]. The relatively low success rate of the PNE and single-stage implant led to the development of the staged implant, whereby the permanent tined lead is inserted and a prolonged external stimulation period is assessed [12]; if successful, then the permanent IPG is implanted. Early reported results with this technique show 80% success rates [12,29]. A pilot prospective randomized controlled trial showed a higher success rate for the two-stage method than for the onestage method [30]. Early results from our department concur with these reports (15 successful procedures from 17 first-stage procedures). The two patients who did not respond had failed the PNE test twice each. However, of the 15 responders, there were two who had had previous unsuccessful PNE tests. Based on our experiences and results, we propose an algorithm for managing women with voiding dysfunction or urinary retention. SNS is only considered in those patients in whom a diagnosis of Fowler s syndrome is made. It is assumed that these patients have had structural or neurological diagnosis excluded (Fig. 5). In conclusion, urinary retention and obstructed voiding can occur in women with no neurological or structural problem. Uncommon in urological practice, it is difficult to diagnose with routine investigations and even with specialist investigation at a national centre of referral a diagnosis is still not always possible. However, women felt that being seen and having an opportunity to discuss their issues at a specialist unit was beneficial, even if a clear diagnosis was not always possible. The only treatment shown to improve voiding is SNS, but this is suitable for only a small proportion of patients. ACKNOWLEDGEMENTS The authors thank Lizzie Boal in help for preparing the manuscript. Funding: Wellcome Trust Grant. CONFLICT OF INTEREST R. Kavia is sponsored by Medtronic and is funded by the Wellcome Trust; R. Dasgupta 2006 BJU INTERNATIONAL 285

6 KAVIA ET AL. FIG. 5. The NHNN management algorithm for women with voiding dysfunction or urinary retention.? Fowler s syndrome/unexplained voiding dysfunction uninary retention Detailed History Non-painful retention Large residual? >1 l Absence of sensations of bladder filling UPP sv Cystometry MUCP > 100 cmh 2 O SV > 1.8 cm 3 Good History for Fowler s Syndrome Large capacity bladder, no sensation of filling Equivocal Normal MUCP normal (92 age) cmh 2 O SV 1.8 cm 3 PNE Unsuccessful Positive Sphincter EMG Normal Consider for staged SNS implantion Consider other diagnosis Undiagnosed condition provided funding for Medtronic; C. J. Fowler has been a paid consultant and study investigator funded by Medtronic. REFERENCES 1 Sokol AI, Jelovsek JE, Walters MD, Paraiso MF, Barber MD. Incidence and predictors of prolonged urinary retention after TVT with and without concurrent prolapse surgery. Am J Obstet Gynecol 2005; 192: Long CY, Hsu SC, Chang Y, Chen YC, Su JH, Tsai EM. The clinical and urodynamic effects of the tension free bladder neck sling procedure. Int Urogynecol J Pelvic Floor Dysfunct 2004; 15: Fowler CJ. Neurological disorders of micturition and their treatment. Brain 1999; 122: Fowler CJ, Kirby RS, Harrison MJ. Decelerating burst and complex repetitive discharges in the striated muscle of the urethral sphincter, associated with urinary retention in women. J Neurol Neurosurg Psychiatry 1985; 48: Fowler CJ, Kirby RS. Abnormal electromyographic activity (decelerating burst and complex repetitive discharges) in the striated muscle of the urethral sphincter in 5 women with persisting urinary retention. Br J Urol 1985; 57: Fowler CJ, Christmas TJ, Chapple CR, Parkhouse HF, Kirby RS, Jacobs HS. Abnormal electromyographic activity of the urethral sphincter, voiding dysfunction, and polycystic ovaries: a new syndrome? BMJ 1988; 297: Swinn MJ, Wiseman OJ, Lowe E, Fowler CJ. The cause and natural history of isolated urinary retention in young women. J Urol 2002; 167: Wiseman OJ, Swinn MJ, Brady CM, Fowler CJ. Maximum urethral closure pressure and sphincter volume in women with urinary retention. J Urol 2002; 167: Edwards L, Malvern J. The urethral pressure profile: theoretical considerations and clinical application. Br J Urol 1974; 46: Kavia RB, Mishra V, DasGupta R, Elneil S, Fowler CJ. Sacral neuromodulation for women with urinary retention. Long term results for the first 30 patients. BJU Int 2005; 95 (Suppl 5): Bosch JL, Groen J. Sacral nerve neuromodulation in the treatment of patients with refractory motor urge incontinence: long-term results of a prospective longitudinal study. J Urol 2000; 163: Spinelli M, Giardiello G, Gerber M, Arduini A, van den Hombergh U, Malaguti S. New sacral neuromodulation lead for percutaneous implantation using local anesthesia: description and first experience. J Urol 2003; 170: Spinelli M, Giardiello G, Arduini A, van den Hombergh U. New percutaneous technique of sacral nerve stimulation has high initial success rate: preliminary results. Eur Urol 2003; 43: Lemieux MC, Kamm MA, Fowler CJ. Bowel dysfunction in young women with urinary retention. Gut 1993; 34: Mousa H, Hyman PE, Cocjin J, Flores AF, Di Lorenzo C. Long-term outcome of congenital intestinal pseudoobstruction. Dig Dis Sci 2002; 47: Lapointe SP, Rivet C, Goulet O, Fekete CN, Lortat-Jacob S. Urological manifestations associated with chronic intestinal pseudo-obstructions in children. J Urol 2002; 168: Vargas JH, Sachs P, Ament ME. Chronic intestinal pseudo-obstruction syndrome in pediatrics. Results of a national survey by members of the North American Society of Pediatric Gastroenterology and Nutrition. J Pediatr Gastroenterol Nutr 1988; 7: Starer P, Likourezos A, Dumapit G. The association of fecal impaction and urinary retention in elderly nursing home patients. Arch Gerontol Geriatr 2000; 30: Meyboom RH, Brodie-Meijer CC, Diemont WL, van Puijenbroek EP. Bladder dysfunction during the use of tramadol. Pharmacoepidemiol Drug Saf 1999; 8 (Suppl. 1): S Malinovsky JM, Le Normand L, Lepage JY et al. The urodynamic effects of intravenous opioids and ketoprofen in humans. Anesth Analg 1998; 87: Petros JG, Alameddine F, Testa E, Rimm EB, Robillard RJ. Patient-controlled analgesia and postoperative urinary retention after hysterectomy for benign disease. J Am Coll Surg 1994; 179: Petros JG, Mallen JK, Howe K, Rimm EB, Robillard RJ. Patient-controlled analgesia and postoperative urinary retention after open appendectomy. Surg Gynecol Obstet 1993; 177: Matsumoto S, Levendusky MC, Longhurst PA, Levin RM, Millington WR. Activation of mu opioid receptors in BJU INTERNATIONAL

7 URINARY RETENTION IN WOMEN the ventrolateral periaqueductal gray inhibits reflex micturition in anesthetized rats. Neurosci Lett 2004; 363: Fowler CJ. Urinary retention in women. BJU Int 2003; 91: DasGupta R, Fowler CJ. Urodynamic study of women in urinary retention treated with sacral neuromodulation. J Urol 2004; 171: Jonas U, Fowler CJ, Chancellor MB et al. Efficacy of sacral nerve stimulation for urinary retention: results 18 months after implantation. J Urol 2001; 165: Scheepens WA, Van Koeveringe GA, De Bie RA, Weil EH, Van Kerrebroeck PE. Long-term efficacy and safety results of the two-stage implantation technique in sacral neuromodulation. BJU Int 2002; 90: Swinn MJ, Kitchen ND, Goodwin RJ, Fowler CJ. Sacral neuromodulation for women with Fowler s syndrome. Eur Urol 2000; 38: Kessler TM, Madersbacher H, Kiss G. Prolonged sacral neuromodulation testing using permanent leads: a more reliable patient selection method? Eur Urol 2005; 47: Everaert K, Kerckhaert W, Caluwaerts H et al. A prospective randomized trial comparing the 1-stage with the 2-stage implantation of a pulse generator in patients with pelvic floor dysfunction selected for sacral nerve stimulation. Eur Urol 2004; 45: Correspondence: Clare J. Fowler, Department of Uro-Neurology, Box 71, National Hospital for Neurology and Neurosurgery, Queen Square, London, WC1N 3BG, UK. c.fowler@ion.ucl.ac.uk Abbreviations: EMG, electromyographic; DO, detrusor overactivity; DSD, detrusorsphincter dyssynergia; MUCP, maximum urethral closure pressure; SV, sphincter volume; PNE, percutaneous nerve evaluation; SNS, sacral nerve stimulation; UPP, urethral pressure profilometry; NHNN, National Hospital for Neurology and Neurosurgery; US, ultrasonography; IPG, implantable pulse generator; CIPO, chronic idiopathic pseudoobstruction BJU INTERNATIONAL 287