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Defecation urgency in irritable bowel syndrome (IBS), a common and devastating symptom, involves sensory as well as emotional components, suggesting that the brain plays as much of a role in urgency as the gut.

A team of Swedish researchers studied adult patients with moderate-to-severe IBS, evaluating their defecation urgency via symptom diaries, questionnaires, and rectal sensation thresholds obtained through rectal balloon distension with a barostat. Structural MRI was conducted to explore potential associations between regional gray matter volume (GMV) and these urgency-related measures.

MRIs revealed that symptom-based urgency differed from barostat-measured urgency in association with GMV in several key regions of the brain.

“Urgency in IBS reflects a multidimensional phenomenon,” Nawroz Barazanji, MD, of the Department of Health, Medicine, and Caring Sciences, Linköping University, Linköping, Sweden, and colleagues wrote.

“Structural brain differences suggest divergent neural substrates, underscoring the importance of distinguishing between experimentally induced and real-life urgency.”

The study was published online in Gastroenterology.

Lived Experience

Defecation urgency, “a sudden and intense need to empty the bowel, often requiring immediate toilet access to avoid or manage the fear of fecal leakage,” is common in patients with IBS and substantially compromises quality of life, according to the authors. Currently, there is no universally accepted definition of “urgency,” which is a lived experience influenced by multiple factors, including stool consistency, rectal fullness, visceral hypersensitivity, increased attention to gut sensations, and central sensitization.

Urgency is a “prominent physiological signal” that captures attention, elicits autonomic and emotional responses, and influences behavior. “The intense and often distressing nature of this symptom therefore suggests engagement of several neural networks responsible for symptom perception. However, little is known about the brain regions involved in the experience of urgency,” the authors stated.

Studies of visceral pain in IBS induced by rectal balloon distention demonstrate altered neural activities in brain regions involved in sensory processing, salience detection, emotional regulation, and autonomic control, especially the anterior cingulate cortex (ACC), insular cortex, and prefrontal regions.

Moreover, neuroimaging studies of bladder-related urgency have pointed to the involvement of various brain networks responsible for the perception, evaluation, and regulation of urinary urgency. Defecation urgency may engage similarly complex neural circuits, the authors suggested.

They therefore set out to enhance the clinical understanding of urgency and its brain structural correlates to IBS. To do so, they distinguished between rectal urgency thresholds — a measure of visceral sensitivity, assessed using rectal balloon distention with a barostat under experimental conditions — vs “real-life urgency,” as experienced in day-to-day life.

They hypothesized that in experimental settings, patients don’t experience the risk for fecal leakage because the rectum is emptied before the procedure and potential fecal passage is blocked by the balloon. The typical anxiety-producing concern is thus removed. Urgency-related sensations must therefore “reflect primary sensory input.” By contrast, real-life urgency “involves a complex interplay of factors” including anxiety about locating a bathroom and the perceived threat of fecal incontinence.

Use Multimodal Approaches

The study included 150 patients (118 women; median age, 34 years; median symptom duration, 12 years) with moderate-to-severe IBS, based on the IBS Severity Scoring System (IBS-SSS). Of these, 32 were subtyped as mixed-type IBS, 55 as constipation-predominant (IBS-C), 57 as diarrhea-predominant (IBS-D), and six as un-subtyped IBS. Of the participants, 137 underwent MRIs.

Participants completed a battery of questionnaires, including the IBS-SSS, the Gastrointestinal Symptoms diary, the Bowel Function Questionnaire (BFQ), the Gastrointestinal Symptom Rating Scale IBS (GSRS-IBS), the Patient Health Questionnaire assessment of somatic symptom burden, the Brief Pain Inventory, the Hospital Anxiety and Depression Scale, and the Visceral Sensitivity Index.

These questionnaires were designed to measure real-life urgency as well as experimentally induced urgency thresholds. Diary and barostat urgency (proportion of bowel movements with urgency and threshold pressure for urgency during barostat testing, respectively) were analyzed as continuous variables and were used in all primary correlation analyses.

BFQ urgency referred to the ability to retain a bowel movement for only 5 minutes or not at all in the absence of an available bathroom, whereas GSRS urgency referred to moderate or greater discomfort.

Diary urgency was higher in the IBS-D vs the IBS-C subgroups (median, 47 (27-70) vs 21 (11-43); P < .001), while no significant difference was found in barostat urgency between subgroups (IBS-D, 25 [20-30] vs IBS-C, 20 [20-25]; P = .2).

Although urgency measures derived from diaries and questionnaires were “strongly intercorrelated,” they showed no significant association with barostat-derived urgency thresholds. Moreover, although all urgency measures were significantly associated with abdominal symptoms, only urgency sensation thresholds were specifically correlated with gastrointestinal-specific anxiety.

Notable differences were found on structural MRI analyses between the two types of urgency.

Symptom-based urgency was associated with reduced GMV in the right and left pregenual ACC (P = .001 and P = .015, respectively) as well as increased GMV in the right amygdala (P < .050). On the other hand, lower barostat urgency was associated with larger GMV in the posterior insula (P = .012), right and left amygdala (P = .007 and P = .006, respectively) and the right hippocampus (P = .014).

Real-life urgency was strongly associated with stool consistency, “reinforcing the notion that loose stools contribute to the sudden need to defecate.” It was also significantly correlated with IBS symptoms severity and somatic symptom burden, including pain.

Heightened visceral interoception and interoceptive hypervigilance “may contribute to the co-occurrence these symptoms by amplifying sensitivity to internal bodily signals,” they suggested. It is possible that repeated fear of fecal incontinence “may contribute to increased central sensitization and symptoms amplification,” suggesting the presence of a “symptom-stress-hyperalgesia loop as part of the gut-brain axis.”

The findings “provide relevant transdisciplinary clinical implications as fecal urgency is a highly distressing symptom not only in IBS but is also commonly observed in other gastrointestinal conditions,” the authors stated.

They recommend “careful clinical assessment and individualized treatment with multimodal approaches, including bowel regulation with medication, neuromodulators, and psychological intervention.”

Study limitations include the absence of a healthy control group and a cross-sectional design, (no causality or temporal relationships could be established).

Beyond the Gut

Commenting for Medscape Medical News, Alan Desmond, MBBCh, consultant in gastroenterology and general internal medicine, Torbay Hospital, UK National Health Service, called the paper “fascinating because it shows that the urgent need to defecate in IBS is not just a bowel symptom but a brain-gut phenomenon.”

Desmond, who wasn’t involved with the study, added, “The findings highlight how urgency is shaped not only by rectal sensitivity but also by emotional and cognitive brain networks, reinforcing the multidimensional nature of IBS symptoms, as well the importance of the brain-gut connection.”

Also commenting for Medscape Medical News, Tedra D. Gray, MSN, APRN, ACNP-BC, adjunct and Rush University and University of Illinois at Chicago and lead management advance practice provider, gastroenterology, Sinai Chicago, described it as a “unique approach to trying to understand the relationship between urgency and gray matter pathway, with a good population size.”

Gray, a spokesperson with the American Gastroenterological Association who was not involved in the study, had one caveat regarding the “discrepancy between imaging and outcomes, and what the researchers were going to do with that information” and how applicable it is in clinical practice. She hopes that this will be elucidated in future studies.

The study was funded by the County Council of Östergötland and the Kamprad Family Foundation. The authors and Desmond disclosed having no relevant financial relationships. Gray reported consulting for Salix Pharmaceuticals.

Batya Swift Yasgur, MA, LSW, is a freelance writer with a counseling practice in Teaneck, New Jersey. She is a regular contributor to numerous medical publications, including Medscape and WebMD.