Association and mechanism

Obesity is considered a strong independent risk factor for both pre-existent and new-onset urinary incontinence in some research studies . The odds ratio attributable to obesity in urinary incontinence varies between 4 and 5. Each five-unit increase in BMI increases the risk of urinary incontinence by 20–70% as reported in a systematic review by Subak et al. The mechanism of stress incontinence is more quickly precipitated by obesity due to the increased intra-abdominal pressure associated with the condition. The increased intra-abdominal pressure leads to an increase in vesical pressure and urethral mobility. The prolonged weakness of the pelvic musculature, nerve supply and supporting structures due to the strain may cause pelvic floor weakness and ineffective function. Overactive bladder symptoms are also reported to be higher in patients with obesity, particularly in the premenopausal age group . The aetiology and pathophysiology of idiopathic overactive bladder is poorly understood even in the general population; hence, no clear mechanism of the association between an overactive bladder and obesity is available.

Obesity and urinary stress incontinence

Stress incontinence has been established to be more common in women with obesity indisputably in many different studies. The dependency of the distressing nature and severity of stress incontinence on increasing BMI is of particular interest . It is then to be expected that weight loss will have a favourable response on the continence mechanism in obese individuals. The effect of non-surgical weight loss has been reported in a health economic analysis . A 5% decrease in weight loss led to a 50% reduction in urinary incontinence episodes. A cost-effectiveness analysis of weight loss and urinary incontinence found a reduction of cost by 21% for a reduction of weight loss by 5% .

Weight loss, by both surgical and non-surgical means, alleviates stress incontinence to a great extent, and it should be considered before any other form of treatment in obese patients reporting distressing urinary stress incontinence. A 40–50% reduction in stress incontinence episodes has been reported after non-surgical weight loss using diet, exercise and medication in some studies . Conservative treatment of stress incontinence comprises pelvic floor exercises, supervised pelvic floor physiotherapy, electrical stimulation of pelvic floor muscles and use of duloxetine. Duloxetine was reported to be a useful alternative in obese patients with a good response in initial studies . More recently, Duloxetine has been described to have anti-obesity and anti-binge eating properties along with its known antidepressant effect in animal studies. The dual effect of this drug may have a favourable impact on stress urinary incontinence in these patients by a variety of mechanisms including facilitation of weight loss .

Stress incontinence is surgically treated by insertion of a tension-free vaginal tape, transobturator tape (TOT), colposuspension, urethral bulking or more recently the single-incision sling insertion without an exit incision. The use of colposuspension has been decreasing since the introduction of the transvaginal tape and TOT. Surgery for stress incontinence is as successful in the obese group of patients as in the general population. A systematic review explored the effectiveness of stress incontinence surgery in obese patients and found it to be equally successful in obese patients as well as patients with normal BMI . Greer et al. obtained similar results in their meta-analysis where an 81% cure rate was quoted in the obese population compared to 85% in the non-obese group . However, specific product studies have observed that obesity is more common in patients with failures after tension-free vaginal tape but not in those with a TOT . A more recent study reported both subjective and objective outcomes after insertion of TOT after a median of 21 months. The results were categorized by BMI. Both subjective and objective results were found to be similar across the various BMI groups . A 1-year follow-up study on 206 patients after insertion of single-incision sling reported its outcomes by BMI groups. A subjective improvement was noted among all the BMI groups, but a lesser objective efficacy was noted with an increasing BMI .

It has also been observed in a case–control study that, compared with the non-obese population, the operating time was more prolonged with a slightly higher estimated blood loss in obese patients undergoing tape procedures for urinary incontinence . It is useful to counsel the patients prior to the procedure with the available evidence and local data on outcomes after incontinence surgery before making an informed decision about surgical treatment among the other options available.

Weight loss and overactive bladder

Whitcomb et al. reported a 73% reduction in overactive bladder symptoms in patients after surgically induced weight loss compared to their baseline symptoms . A similar reduction in distressing overactive bladder symptoms has been described in studies with non-surgical weight loss .