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We now know more about incidence, the fascial sling versus Burch colposuspension, complication rates of mid-urethral slings, and Botox for detrusor overactivity

December 2007 · Vol. 19, No. 12


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The author reports no financial relationships relevant to this article.

The past year has seen the publication of much useful evidence regarding urinary incontinence, from both epidemiologic studies and clinical trials. Research into the pathophysiology of incontinence continues to move forward, slowly but surely, measured not in breakthroughs but in gradually increasing knowledge of how the urethra and bladder function in the continent person and how that function can break down, leading to incontinence and other urinary symptoms.

Highlighted here are four notable studies from 2007, as well as progress notes on a trial mentioned early this year in Examining the Evidence (January issue).

New data clarify incidence and uncloak the effect of weight gain

Townsend MK, Danforth KN, Liffort KL, et al. Incidence and remission of urinary incontinence in middle-aged women. Am J Obstet Gynecol. 2007;197:167.e1–167.e5.

Townsend MK, Danforth KN, Liffort KL, et al. Body mass index, weight gain, and incident urinary incontinence in middle-aged women. Obstet Gynecol. 2007;110:346–353.

Studies of urinary incontinence in numerous populations have reported its prevalence—i.e., the percentage of people who have the condition at any point in time—but few have attempted to define its incidence—i.e., the rate at which it develops during a defined period.

Incidence is a true rate, described with a unit of time in the denominator. Prevalence is not a rate (although it is commonly referred to as such) and is described as a percentage only, without time in the denominator. With that distinction in mind, it is easy to see why prevalence data greatly outnumber incidence data: Prevalence can be obtained by means of cross-sectional study, with one-time collection of data. In contrast, incidence data require a population that is free of the condition of interest at baseline; that population is then followed to determine how many people who were initially free of the condition go on to develop it.

Lack of a standard definition makes it hard to measure incontinence

Reported prevalence can range from less than 10% to more than 90%, depending on how incontinence is defined:

  • Very low prevalence is found when the definition is limited to persons with the greatest severity or frequency of symptoms
  • at the other end of the spectrum, very high prevalence—even approaching 100%—can be found using a definition that includes people who have “ever” leaked urine.

The same issues complicate estimates of incidence. Because there is no consensus over what constitutes a clinically significant threshold for incontinence, investigators are forced to develop their own definitions.

In a pair of studies, Townsend and colleagues neatly circumvent this problem. Using data from the Nurses’ Health Study II, they used a series of definitions of incontinence, ranging from less severe to more severe, to describe their findings in ways that are easily transferred to clinical practice. They focused their attention on women aged 36 to 55 years to estimate the incidence of incontinence over a 2-year period. At baseline, women were considered at risk of incident incontinence if they reported never leaking or leaking only a few drops less than once a month. Three categories of incontinence were then defined, based on symptoms 2 years later:

  • incident incontinence: any urine loss, defined as leaking 1–3 times a month
  • frequent incontinence: urine loss at least once a week
  • severe incontinence: urine loss at least once a week of sufficient volume to at least wet underwear.

Incidence rose with BMI, weight gain

In almost 34,000 continent women from 2001 to follow-up in 2003, the overall (average) incidence of urinary incontinence was 6.9 women for every 100 woman-years. Frequent incontinence developed in, on average, 1.8 women for every 100 woman-years; severe incontinence, in 0.6 women for every 100 woman-years.

Using multivariable logistic regression models, the authors analyzed the likelihood of incident incontinence by body mass index (BMI) and estimated weight gain from the age of 18 until 2001. For either variable, odds ratios (OR) showed a highly significant trend (P<.001) for an increased risk of incident incontinence.

For example, at a BMI greater than 35 kg/m2, the likelihood of:

  • any incontinence increased by a factor of about 2 (OR, 2.11; 95% confidence interval [CI], 1.84–2.42)
  • frequent incontinence increased by a factor of almost 4 (OR, 3.85; 95% CI, 3.05–4.85)
  • severe incontinence increased by a factor of more than 5 (OR, 5.52; 95% CI, 3.72–8.18).

The trend for weight gain was similar, with a gain of more than 30 kg showing odds ratios and 95% confidence intervals of similar magnitude to those seen with a BMI greater than 35.

But one third of incontinent women improved after 2 years

Although urinary incontinence is usually understood as a chronic condition, albeit under the influence of other factors, such as weight gain, data on remission are even scarcer than data on incidence. Using the same dataset, the authors determined that almost 31,000 women were incontinent at baseline in 2001, with incontinence occurring at least monthly. Complete remission, defined as no leaking in 2003, occurred in almost 14% of women. One third reported improvement, defined as either complete remission or a decrease in leaking frequency from 2001 to 2003.

It’s interesting that complete remission was more common in younger women. It also was more common in women who experienced frequent incontinence than in those who reported occasional incontinence. The remaining percentage of women—almost 60%—reported a similar or increased frequency of incontinence over the 2 years of follow-up.

The authors did not collect data on treatment. Estimates of persistence, improvement, and remission could be affected, therefore, if women received effective treatment between 2001 and 2003. However, only about one third of women reported mentioning their symptoms to a physician, and only 13% reported receiving treatment for incontinence. The magnitude of the effect of treatment on remission or improvement of urinary incontinence symptoms therefore seems limited.

Women remain reticent about incontinence

Several points underline the clinical importance of these data, including the relatively high incidence of incontinence symptoms and the strong influence of BMI and weight gain on that incidence. Also notable, and described in previous studies, is the vast underreporting and undertreatment of incontinence in women—an observation that should motivate all clinicians to include screening for urinary incontinence as part of regular well-woman care. Clinicians should also be prepared to refer women with incontinence or to initiate evaluation and management.

Some reports have suggested that the stigma of urinary incontinence has diminished slightly in light of widespread direct-to-consumer advertising for products related to the care (e.g., pads) or treatment (e.g., pharmaceuticals) of incontinence. The data from Townsend and colleagues are relatively recent, yet the majority of women failed to report their symptoms, and an even higher percentage received no treatment. The authors recommend that health-care providers initiate a discussion of urinary symptoms even in middle-aged women, who may be targeted for screening less frequently than older women.

In fascial sling vs Burch, sling prevails but is linked to more adverse effects

Albo ME, Richter HE, Brubaker L, et al, for the Urinary Incontinence Treatment Network. Burch colposuspension versus fascial sling to reduce urinary stress incontinence. N Engl J Med. 2007;356:2143–2155; comment: 2198–2200.

Eagerly anticipated results of the Urinary Incontinence Treatment Network’s first surgical trial, which compared the fascial sling procedure with Burch colposuspension for stress incontinence, were published in May in the New England Journal of Medicine. The Urinary Incontinence Treatment Network is a multicenter clinical trials group that was established in 2000 and is sponsored by the National Institutes of Health (specifically, by the National Institute of Diabetes and Digestive and Kidney Diseases and the National Institute of Child Health and Human Development).

Women were eligible for the trial if they experienced symptoms of stress incontinence; symptoms of mixed incontinence were allowed as long as stress symptoms predominated. Of 655 women in the trial, 326 were randomly assigned to undergo placement of an autologous rectus fascia pubovaginal sling, and 329 were randomized to Burch colposuspension.

Overall success was defined as:

  • negative pad test
  • no urinary incontinence reported in a 3-day diary
  • negative stress test to cough and Valsalva maneuver
  • no self-reported symptoms of stress incontinence
  • no retreatment for stress incontinence.

“Stress success,” or stress continence, was defined using the last three criteria.

At 2 years after the index surgery, 520 women (79%) were available for follow-up. Overall success and stress success were slightly higher in women who underwent sling placement than in those treated by Burch: overall success, 47% versus 38%, and stress success, 66% versus 49%, respectively. However, women who had slings experienced more adverse outcomes, including urinary tract infection, difficulty voiding, and postoperative urge incontinence.

Success rates were much lower than previously reported

These findings are particularly striking because the success rates are lower than in previous reports—and lower than the figures commonly used by surgeons to counsel women about likely results. “Success” for either procedure has been commonly quoted in the 80% to 90% range, not the 30% to 40% range found here. The authors are to be commended for the stringent definition of “success,” which included elements that invariably result in a lower success rate. It is these numbers that women are most interested in when they are considering this type of surgery.

The difference between sling and Burch procedures was particularly remarkable in regard to stress success (17 percentage points). The smaller difference seen for overall success (9 percentage points) can be attributed to the increase in postoperative urge incontinence among women undergoing the sling procedure.

If the other adverse events associated with the sling procedure (i.e., urinary tract infection and voiding difficulty) had been included in the composite measure of success, it seems possible, if not likely, that a smaller difference—or no difference at all—would have been seen between the sling and Burch groups.

Additional data still to come

Follow-up of women in this trial has been extended for up to 5 years and should provide much-needed information on longer-term results after these surgeries.

Transobturator mid-urethral sling linked to fewer complications

Sung VW, Schleinitz MD, Rardin CR, Ward RM, Myers DL. Comparison of retropubic versus transobturator approach to mid-urethral slings: a systematic review and meta-analysis. Am J Obstet Gynecol. 2007;197:3–11.

In this Update 1 year ago, I remarked on the need for more comparative information about the various mid-urethral slings currently on the market, particularly in regard to complications—information necessary to make recommendations and guide clinical decision-making.

Originally, the procedure for mid-urethral sling placement was modified from the retropubic approach to the obturator approach with the aim of reducing the risk of major bladder and urethral injury and vascular complications (FIGURE 1). Recent data suggest that that goal has been achieved. In a systematic review and meta-analysis of 17 studies that compared retropubic and transobturator approaches, Sung and colleagues found the transobturator route to be associated with fewer complications.

FIGURE 1 Transobturator approach lives up to promise

The retropubic approach (A) was modified to create the transobturator approach (B), with the aim of protecting the bladder, urethra, and vascular structures. A recent meta-analysis indicates that this goal was achieved.

Subjective and objective outcomes were similar for the two approaches

Overall, 492 women in six trials were randomly assigned to receive either a retropubic or transobturator mid-urethral sling for treatment of stress incontinence. Although some trials specified exactly which device was used, others did not. Follow-up ranged from 1 to 15 months.

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