From Gut Feeling to Gray Matter: Mapping Defecation Urgency in Irritable Bowel Syndrome.

Abstract

Defecation urgency is a common and highly distressing symptom in patients with irritable bowel syndrome (IBS), but its definition remains insufficiently clear. We aimed to compare different measures of urgency, real-life and rectal sensation thresholds, their clinical and neural correlates. A total of 150 patients with moderate-severe IBS were enrolled in this cross-sectional study conducted at a specialized gastroenterology clinic. Defecation urgency was evaluated using gastrointestinal symptom diaries, questionnaires, and rectal sensation thresholds. Structural magnetic resonance imaging (MRI) was performed to explore associations between regional gray matter volume (GMV) and urgency-related measures. Statistical analyses were conducted using non-parametric tests and partial correlation analyses, adjusted for relevant covariates. A p-value of < 0.05 was considered statistically significant. Urgency measures derived from diaries and questionnaires were strongly intercorrelated but showed no significant association with barostat-derived urgency thresholds. All urgency measures were significantly associated with abdominal symptoms, yet only urgency sensation thresholds were specifically correlated with gastrointestinal-specific anxiety. Structural MRI analyses revealed that symptom-based urgency was associated with reduced GMV in the right (p=0.001) and left (p=0.015) pregenual anterior cingulate cortex and increased GMV in the right amygdala (p<0.050). In contrast, lower barostat urgency was associated with larger GMV in the posterior insula (p=0.012), right (p=0.007) and left (p=0.006) amygdala, and right hippocampus (p=0.014). Urgency in IBS reflects a multidimensional phenomenon involving sensory and emotional aspects of gastrointestinal burden. Structural brain differences suggest divergent neural substrates underscoring the importance of distinguishing between experimentally induced and real-life urgency.