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Overactive bladder (OAB) describes the symptoms of urinary urgency, frequency, nocturia and urge incontinence that affect approximately 16% of women in the USA . Many women with OAB do not have incontinence, with an estimated prevalence of 7.6% for continent/dry OAB , but incontinence occurs in ≈ 50% of patients presenting clinically with OAB symptoms . Urinary urgency and frequency are the most common symptoms associated with OAB. While these symptoms of urgency, frequency and incontinence have been shown to significantly impact health-related quality of life, urinary urgency was found to be more bothersome than incontinence itself . Unfortunately, the exact pathophysiology of dry OAB symptoms remains unclear.
Clinical observation suggests that women with dry OAB often have increased pelvic floor muscle activity and dyskinesia interfering with muscle relaxation. In the 2005 report of the ICS Clinical Assessment Group, the descriptor ‘ Overactive Pelvic Floor Muscles ’ was accepted as standard terminology for pelvic floor muscles that do not relax fully or contract when full relaxation is necessary . There are several possible mechanisms by which overactive pelvic muscles may contribute to OAB symptoms. The pelvic floor muscles have a close anatomical relationship to the urethra and bladder neck. Changes in muscle function may lead to a change in the resting angle of the urethrovesical junction, which could cause irritation of the urethra or bladder neck. Alternatively, underlying neurological abnormalities may lead to pelvic floor muscle changes as well as LUTS. These changes could occur at the level of the peripheral nerves or the sacral nerve reflexes, particularly the guarding reflex. Numerous studies have linked overactive pelvic floor muscles on clinical examination and surface electromyography (sEMG) measurements to various pain syndromes including interstitial cystitis, back pain and vulvar vestibulitis [4–8]. Evidence suggests pelvic floor muscle sEMG measurements differ in women with these pain syndromes compared with asymptomatic women . Furthermore, normalizing the muscle performance with sEMG biofeedback improved symptoms [9–12]. Research has also shown differences in pelvic floor muscle sEMG measurements in women with stress urinary incontinence compared with age-matched normal women ; however, no study to date has described pelvic muscle sEMG measurements in women with dry OAB symptoms compared with asymptomatic women to determine whether there are differences.
The primary aim of the present study was to determine if pelvic floor muscle sEMG measurements differed in women with dry OAB symptoms compared with asymptomatic controls. We hypothesized that women with dry OAB would be less able to relax their pelvic floor muscles and would exhibit higher resting muscle activity and decreased ability to relax between contractions.. The secondary aim of the study was to determine whether pelvic floor muscle performance was associated with anxiety scores, quality of life and life stress measures. As an exploratory analysis, we also investigated whether there were differences in anxiety scores, quality of life, and life stress measures among those women with dry OAB compared with controls.
Women aged 18–55 years of age were recruited for this study. The study protocol was approved by the Institutional Review Board at the University of California, San Francisco, and all patients gave informed consent. We recruited symptomatic women reporting ≥ 10 voids per day and asymptomatic women reporting ≤ 7 voids per day. Participants were recruited from flyers posted at the UCSF Medical Center, the San Francisco State University campus, a San Francisco YMCA, and from advertisements posted in the community from November 2007 to August 2008. A designated study recruiter determined eligibility during a telephone interview and enrolled participants who met all eligibility requirements.
Women who reported urinary incontinence, use of skeletal muscle relaxant medications within the past 3 months, current diuretic use, bladder infection, prior hysterectomy, 24-h fluid intake > 2.5 L, congestive heart failure or any diagnosis known to potentially affect pelvic floor muscle function including vulvar vestibulitis, multiple sclerosis, type I diabetes, chronic pelvic pain, spinal stenosis and prior anti-incontinence surgery were excluded from this study. Postmenopausal women without a period for at least 6 months and pregnant women were excluded due to possible confounding of effects attributable to hormonal influences on the pelvic floor muscles. Those with psychiatric disease or those who were HIV positive were excluded.
Participants were enrolled concurrently into either the ‘ case ’ or ‘ control ’ group. In order to enroll participants of similar age in each group, once 14 case and 14 control participants were enrolled, the recruiter enrolled the next 14 case and control participants, age-matching participants within a 5-year age range. We screened an additional 124 women for the study who either did not meet inclusion criteria (n = 85), were unable to attend the two required visits (n = 25), reported accidental leakage (n = 12), or were not interested in participating (n = 2).
We performed a prospective case-control study to determine whether there were differences in pelvic floor muscle sEMG measurements in women with dry OAB symptoms compared with asymptomatic women. We also investigated whether pelvic floor muscle sEMG measurements were associated with anxiety scores, quality of life, and life stress measures.
At the first visit, eligible participants completed a dipstick urine analysis to exclude a UTI, and were given a 2-day bladder diary to complete and return in a stamped envelope. Once the bladder diary was returned, study personnel reviewed the diary to confirm appropriate inclusion criteria and enrolled eligible participants in the study case or control group.
Once enrolled, participants were scheduled for the second visit. At this visit, the participants underwent pelvic floor muscle testing using Pathway MR20 Dual Channel EMG System (Prometheus, Dover, NH, USA) with a vaginal sensor (Pathway vaginal sensor #6330; Prometheus) while positioned supine on the examination table with head and knees each supported by a pillow. Participants placed the sensor themselves, as instructed by the researcher. Water was used as a lubricant. Participants were initially instructed to contract and relax the pelvic floor muscles while observing the monitor but were not allowed to observe the monitor during the testing. The sEMG testing included a verbally cued 30-s baseline rest, followed by 10 repetitions of 2-s contraction and a 4-s rest, 10 repetitions of 10-s contractions and a 10-s rest, and a 30-s relaxation at completion (Time 1). After the initial sEMG testing, participants removed the sensor and completed the following questionnaires: demographics, Beck Anxiety Inventory, Pelvic Floor Distress Inventory, Pelvic Floor Impact Questionnaire and Recent Life Changes Questionnaire. Pelvic floor muscles were then re-tested with sEMG using the same testing protocol (Time 2). Participants were instructed not to discuss their bladder symptoms during the testing. The status of the recruited participants and controls was blinded to the examiner.
The primary outcome measures were recorded in mean microvolts (mv) of muscle activity, and included pretest and post-test resting baseline, sd of the pretest and post-test resting baseline, phasic contractions (3-s), and tonic contractions (10-s). Between-trial reliability has been previously reported with vaginal sEMG and varies (Intraclass correlation = 0.58 – 0.98 to 0.0.58 – 0.98) depending upon the sensor. (Auchincloss, 2009) We used the Time 1 sEMG measurements in the analysis.
For aim 1, a sample size of 28 in each group had 80% power and two-tailed significance level ofP= 0.05 to detect a difference of 1.3 microvolt (mv) . This estimate is based on sd values of 2.043 mv and 1.067 mv for resting baseline among symptomatic and asymptomatic women with dysesthetic vulvodynia .
We tested case and control differences in demographic variables, sEMG measurements and anxiety, quality of life and life stress questionnaires using an unpairedt-test. We used factorial anova to test for differences in sEMG measurements while controlling for group, time and interaction between group and time effects. The Pearson correlation coefficient (r) was used to determine whether sEMG measurements were associated with anxiety, quality of life and life stress measures. All analyses were implemented in SAS Version 9.2 (SAS Institute, Cary, NC).
A total of 56 participants were enrolled and all 56 women completed the study (Table 1). There was a significant difference in number of voids per day among women with dry OAB and controls,P < 0.001. Among women with dry OAB, we observed an 325 cc lower fluid intake, a smaller proportion of participants reporting excellent health, and greater numbers of current smokers compared with controls, although these differences were not signficant.
Women with dry OAB had higher Beck Anxiety Inventory scores than controls, (P = 0.032). They also scored significantly higher on the Pelvic Floor Distress Inventory and Pelvic Floor Impact Questionnaire (Table 2). No difference was noted in life stress scores between women with dry OAB and controls.
There were no significant differences found in sEMG measurements of pelvic floor muscle performance between the two groups (Table 3). Post-test resting baseline measurements were lower among controls than in with women with dry OAB, but were not significantly different. There was a significant effect of time in the Time 1 and Time 2 repeat measurements of resting baseline, SD of resting baseline and resting between contractions, however, there was no case effect (P = 0.32) and interaction between case and time was not significant (P = 0.82). We used Time 1 measurements for all sEMG comparisons after finding no difference in the outcomes using Time 2 measurements.
There was a positive correlation between sEMG pretest resting baseline and Beck Anxiety Inventory,r= 0.29, however, it did not reach statistical significance. There was no significant correlation observed between sEMG pretest resting baseline measurements and the Pelvic Floor Distress Inventory, Pelvic Floor Impact Questionnaire, life stress scores among symptomatic women (P > 0.05)
Anxiety scores were significantly higher in women with dry OAB. The present study supports a relationship between dry OAB symptoms and anxiety that could represent an underlying response to stress as a mediator for OAB symptoms. Limet al.  previously described higher anxiety scores in patients with mixed urinary incontinence than in those with pure stress incontinence. Additionally, it has been reported that individuals who have changes in day-to-day activities related to urinary incontinence are more likely to meet criteria for an anxiety disorder . While it is not clear if anxiety is a causal factor for OAB symptoms or results from having these bladder symptoms, the relationship between anxiety and OAB warrants further exploration.
We did not find significant differences in any sEMG measurements of the pelvic muscle. Dry OAB symptoms are probably caused by several different etiologies and physiological abnormalities, therefore, it is possible that there is a subset of patients who do have abnormal muscle performance as a cause of these symptoms, but this could not be identified in a heterogeneous group of participants. The physical examination was limited to the sEMG testing; we did not include pelvic floor muscle palpation to assess the ability to relax. While we hypothesized that women with dry OAB were unable to relax their pelvic floor muscles, it is possible the muscles in women with dry OAB are chronically short and tight yet not excessively contracted and therefore the resting sEMG baselines were not elevated as hypothesized.
Although no differences were noted in the life stress scores between women with dry OAB and controls, it is important to note that only the 6 months before enrollment were assessed. Several participants commented that if the time interval had been extended to a year or longer, the number of positive answers would have been much higher. Since many of the participants had long-standing OAB symptoms, it is also possible that life stress scores measured for a longer time period or at the onset of symptoms may yield different results.
As expected, women with dry OAB had significantly higher scores on the Pelvic Floor Distress Inventory and Pelvic Floor Impact Questionnaire because these texts are designed to assess severity of urinary symptoms.
We recognize that the present study has several limitations. First, we used sEMG measurements rather than wire electrodes, transperineal ultrasound or manual palpation to detect differences in muscle performance. Visualizing the lift and descent of the pelvic floor muscle with ultrasound or palpation might have provided additional information about the ability to relax the pelvic floor muscle. Second, there is between-trial variability in pelvic floor muscle performance with sEMG that could have decreased the accuracy of the testing, although the differences we observed between trials did not vary by group. Third, it is possible that there was cross-talk from other muscles using the sEMG but this would probably not affect the ability to relax the pelvic floor muscles. Fourth, we did not assess postvoid residuals and therefore did not rule out urinary retention, although this is a relatively uncommon finding in patients with dry OAB. Additionally, because examinations and urodynamic studies were not performed on participants, the symptomatic group probably represents a heterogeneous group with regard to etiology of OAB symptoms, which could include sensory urgency, motor detrusor overactivity and pelvic muscle dysfunction. We also recognize that there is some overlap in patients with dry OAB and painful bladder syndrome/interstitial cystitis. It is possible that some patients with these diagnoses were included, although we attempted to limit this possibility by excluding all patients who reported pelvic or vulvar pain. Fifth, participants and controls were recruited from the community and may have had an interest in urinary issues that could introduce unrecognized bias. However, this would probably apply to both women with dry OAB and controls and would have a non-differential effect on the outcome. Lastly, it is important to note that since this is a pilot study, an inadequate statistical power in this sample may limit us from detecting potential underlying effects or drawing conclusive results.
In conclusion, we found that anxiety scores were significantly higher in women with dry OAB than in asymptomatic controls. This study showed no significant differences in pelvic floor muscle sEMG measurements in women with dry OAB compared with controls. Further investigation of the association between anxiety and dry OAB in a longitudinal study may provide insights into the temporal relationship between anxiety and dry OAB.
Abnormal pelvic floor muscle function has been associated with chronic pelvic pain syndromes.
This study adds evidence about pelvic muscle performance in women with dry overactive bladders.
We acknowledge the Pfizer Global Investigator Initiated Research grant.
CONFLICT OF INTEREST
Wendy B. Katzman is a Study Investigator funded by the Sponsor.