It is estimated that more than 20% of women over the age of 40 years, experience overactive bladder (OAB) symptoms,1 with a significant negative impact on their mental and physical health and sexual function.2 If conservative management is unsuccessful, women may be offered treatment with intravesical Botulinum Toxin A (BoNT/A) to manage refractory OAB symptoms.
The association between obesity and urinary incontinence is well-recognised,3 however the influence of obesity on treatment efficacy is poorly understood. We hypothesised that high Body Mass Index (BMI) has a negative impact on treatment outcomes following intradetrusor BoNT/A injection for OAB.

This is a retrospective cohort study of women who received at least one BoNT/A injection for the treatment of refractory OAB between August 2013 and January 2023, in a tertiary Urogynaecology centre in the United Kingdom. Patients were identified from the British Society of Urogynaecology (BSUG) database. Demographic data collected included age, BMI, and dose of BoNT/A administered. All patients completed the International Consultation on Incontinence Questionnaire – Overactive Bladder (ICIQ-OAB) questionnaire before and six months after treatment. This is a validated, objective tool for the assessment of symptom severity and impact on quality of life. Information on pre- and post-treatment ICIQ-OAB scores and the subjective measure of treatment satisfaction was collected. Data on the length of time following administration of BoNT/A and return of symptoms was also recorded.
The primary outcome was the impact of BMI on pre- and post-treatment ICIQ questionnaire scores and treatment satisfaction.
Secondary outcome was the impact of BMI on duration of treatment efficacy.

An initial selection of 522 patients were identified, and after removal of duplicates and those with inaccurate or missing data, a cohort of 370 cases with at least one recorded outcome measure, remained. Patients were grouped according to BMI, with the categories as follows: BMI ≤25, BMI 26-30, BMI 31-35, BMI 36-40, BMI ≥ 40.

Of the 288 cases where satisfaction was recorded at 6-month follow up, 78.6% (44/56) in those with a BMI ≤ 25, 78.8% (69/87) in those with BMI 26-30, 67.2% (43/64) in the BMI 31-35 group, 88.5% (47/53) in the BMI 36-40 group, and 77.8% (22/28) in those with BMI ≥ 40, were satisfied with the treatment (Table 1). There was no significant difference in satisfaction rates between the different BMI groups (p= 0.105).

132 cases had pre-and post-treatment ICIQ-OAB scores recorded (Table 2). The mean change in ICIQ-scores in each BMI category, BMI ≤25, BMI 26-30, BMI 31-35, BMI 36-40, BMI ≥ 40, were 0.34±3.64, 0.39±2.93, 0.08±3.71, −0.36±3.78, −0.58±2.02, respectively. Again, there was no statistically significant difference in change in ICIQ-OAB score when different BMI categories were compared (p=0.843)

To determine whether BMI affected the duration of efficacy treatment, the number of days between BoNT/A administration and return of symptoms was calculated. 335 cases were included in this analysis, with an average treatment efficacy duration of 202 days (range 0-2425 days). When divided into BMI categories, average duration of treatment efficacy did not show any statistically significant difference between groups (p=0.187). (Table 3)

These results show that there is no statistically significant difference in either objective or subjective outcome measures, or duration of efficacy of intravesical BoNT/A for the treatment of refractory OAB symptoms based on BMI. Limitations of the study include the small numbers of patients in each BMI category. Other outcomes, such as the incidence of post-treatment complications according to BMI could also be considered.

BMI does not affect the efficacy of intravesical BoNT/A injection for the management of refractory OAB symptoms. Intravesical BoNT/A should not be excluded/rationalised as a treatment option on the basis of BMI alone.

Coyne, K. S. et al. The prevalence of lower urinary tract symptoms (LUTS) in the USA, the UK and Sweden: results from the Epidemiology of LUTS (EpiLUTS) study. BJU Int 104, 352–360 (2009).
Abrams P, Kelleher CJ, Kerr LA, Rogers RG. Overactive bladder significantly affects quality of life. Am J Manag Care. 2000 Jul;6(11 Suppl):S580-90
Hunskaar S. A systematic review of overweight and obesity as risk factors and targets for clinical intervention for urinary incontinence in women. Neurourol Urodyn. 2008;27(8):749-57.