Rectal sensory tests are not routinely performed on patients undergoing sacral nerve stimulation (SNS). The aim of this study is to determine the rectal sensory function in patients responding to SNS treatment for faecal incontinence (FI) and constipation.Method
Patients complaining of either FI (group I) or constipation (group II) who underwent rectal sensory testing and SNS treatment between 2003–2013 were selected. Group I (F:M≥113:15, age ≥20–74 years) underwent rectal mucosal stimulation using Gaeltec rectal electrosensitivity (RES) bi-polar catheter. Group II (F:M≥39:2; age ≥24–50 years) underwent rectal sensitivity to distension using Stericom Ashley2 reflex balloon catheter.Method
The RES electrodes were placed in contact with the rectal mucosa and stimulus was passed with the current increasing by 0.1 mA/s until patient reported rectal sensation (tingling, buzzing or throbbing) (normal RES thresholds to elicit sensation has been reported ). RES testing was repeated 3 times per patient and the lowest current intensity to induce sensation was recorded. RES thresholds were compared between SNS treatment outcomes using t-test. Receiver operating curve (ROC) was used to find the optimal RES threshold for successful SNS outcome. Odd ratio (OR) and positive predictive value (PPV) were calculated at the optimal RES threshold.Method
The balloon catheter was inserted into the rectum, inflated at 1–3 ml/s and patient’s sensory perceptions to threshold volume (TV), urge volume (UV) and maximum tolerated volume (MTV) were recorded.1 These sensory markers were used to ascertain normal and hypo rectal sensitivities in patients with successful SNS outcome. t-test was used to compare TV, UV, and MTV sensory markers in the SNS outcomes.Results
All patients in group I respond within normal RES thresholds. RES thresholds in the successful SNS group were statistically significantly higher (p≥0.029) suggesting patients responding to lower RES thresholds have increased sensitivity and do not find SNS treatment beneficial. The optimal RES response condition for successful SNS outcome was when>18 mA which has significantly higher success rate (OR ≥3.1, PPV ≥72% and p≥0.015).Results
68.3% of patients in group II respond to SNS. Surprisingly, the sensory 3 markers were either all normal or abnormally elevated (hyposensitive) in each patient without crossover. Normal rectal sensory markers are generally found in patients with successful SNS outcome (TV, p≥0.0458; UV, p≥0.0150; MTV, p≥0.003). 83% of patients with normal rectal sensory responded to SNS and 62% of patients with rectal hyposensitivity did not respond to SNS (p≥0.0036).Conclusion
This study shows normal rectal sensory function plays a role in successfully treating patients with SNS.