Sacral Neuromodulation therapy (SNM) is a surgical treatment for overactive bladder and voiding dysfunction. The treatment usually consists of two stages: a trial phase and a permanent implantation (or removal).  At present, there are few factors which can reliably predict treatment success. In recent times, some have suggested that Body Mass Index (BMI) and age may influence success and complications. We hypothesise that BMI and age do not have a statistically significant impact on trial success, nor do they increase the likelihood of complications.

74 consecutive cases (68 female, 4 male) of patients who underwent first stage SNM procedures between 2016 and 2020 were analysed retrospectively. All patients had been diagnosed as having voiding dysfunction, overactive bladder or both. BMI (mean 33.19 kg/m2, SD = 7.96) and age (mean = 45.73 years, SD = 15.93) were recorded at the time of their surgery. Success was considered to be at least 50% reduction in bothersome symptom and thus implantation of permanent neurostimulator. Complications were defined as loss of efficacy, infection or stimulation pain requiring the need for revision of tined lead occurring within a five-year follow-up period. 

Binary logistic regression was performed to evaluate the association of age and BMI with treatment success and separately with complications. Odds Ratios (OR) with 95% Confidence Intervals (CI) were calculated, and statistical significance was defined as p < 0.05.

All 74 cases were included in the analysis. BMI was not significantly associated with success (p = 0.343, OR = 0.965). Lower age was associated with a modest, but statistically significant, higher likelihood of success (p = 0.042, OR = 0.956). BMI was not significantly associated with complications (p = 0.250, OR = 1.038). Age was not significantly associated with complications (p = 0.066, OR = 0.968).

BMI does not appear to be a predictor of trial success, nor complications. Lower age appears to somewhat predict treatment success with each additional year decreasing the odds of success by 4.4%. Age does not appear to be correlated with increased levels of complications.

Preliminary results suggest that BMI does not predict treatment success, but lower age seems to increase chances of success to some degree. Complications are not influenced by either factor. It is possible that those with higher BMI and increased age fair as well as others.  

The study is limited by the sample size. It would also be useful to understand whether these factors affect other metrics, such as stimulation parameters, neurostimulator battery life and direct symptom resolution. Further work will aim to address these limitations.