Sacral nerve stimulation changes rectal sensitivity and biomechanical properties in patients with irritable bowel syndrome

BackgroundSacral nerve stimulation (SNS) has been demonstrated to alleviate symptoms and improve quality of life in selected patients with irritable bowel syndrome (IBS). The mechanisms of action, however, remain unknown. The aim of the study was to evaluate the effects of SNS on rectal sensitivity and biomechanical properties in patients with IBS. MethodsTwenty patients with diarrhea-predominant (n=11) or mixed (n=9) IBS were treated with SNS in a controlled, randomized crossover trial. They were randomized to either 1month of SNS (ON) or placebo (OFF) with the opposite setting for the next month. Sensory and biomechanical parameters were assessed by multimodal rectal stimulation at the end of each period. IBS-specific symptoms were evaluated at baseline and at the end of each treatment period. Key ResultsCold stimuli were better tolerated in the ON period (19.9 degrees C[0.6]) compared to the OFF period (21.8 degrees C[+/- 0.6]; p=0.03). Significantly lower cross-sectional areas were needed to elicit sensory responses in the ON period (1545mm(2)[+/- 95]) compared to the OFF period (1869mm(2)[+/- 92]; p=0.015). The association between reduced sensory threshold and improvement of constipation was of borderline significance (p=0.05). Wall stiffness was significantly lower in the ON period (192mmHg[+/- 10]) compared to the OFF period (234mmHg[+/- 10]; p=0.004). Reduced wall stiffness was significantly associated with improved overall GSRS-IBS symptom score (p=0.01). Reduced sensory threshold to stretch (p=0.02) and reduced wall stiffness (p<0.001) were predictors of the GSRS-IBS symptom score. Conclusions & InferencesSNS for diarrhea-predominant and mixed IBS relaxes the rectal wall, while making it more sensitive to stretch and less sensitive to cold. Reduced wall stiffness and increased sensitivity to stretch are associated with improved GSRS-IBS symptom score.