Introduction

Functional bowel disorders are characterized by the presence of altered bowel habits with or without abdominal pain.¹ Irritable bowel syndrome (IBS) is diagnosed based on recurrent abdominal pain; however, distinctions in the clinical phenotypes of IBS subtypes and other functional bowel disorders (FBDs), such as functional diarrhea (FD) and functional constipation (FC), remain underexplored.^2,3

Aims & Methods

Aims: This study aimed to characterize the clinical presentation of IBS with predominant constipation (IBS-D) and IBS with predominant diarrhea (IBS-C), differentiating them from FD and FC, while recognizing the overlapping symptoms and the continuum between these conditions. Additionally, we examined the prevalence of psychological disorders and extra-intestinal comorbidities and identified potential mediators linking IBS to anxiety and depression.
Methods: Using data from the Rome Foundation Global Epidemiology Study, we analyzed 54,127 participants across 26 countries, including 2,195 patients with IBS. Clinical, dietary and psychological characteristics were assessed using validated questionnaires. Subgroup analyses compared IBS subtypes with FBDs, while mediation analyses (using the PROCESS macro and Baron and Kenny's method⁴) identified mediators of IBS-psychological distress relationship.

Results

As compared to patients with IBS-D, patients with IBS-C reported more severe pain characteristics, including prolonged pain episodes (50.7% vs. 47.0% of the time with pain lasting >30 minutes, p=0.030) and pain episodes that escalated to a sustained severe intensity (44.2% vs. 38.1%, p=0.026), frequently accompanied by back pain (36.7% vs. 30.9%, p<0.001). Regular use of prescribed pain medications was also more frequent in IBS-C (39.3%) than IBS-D (31.8%, p=0.004). In contrast, as compared to IBS-C, patients with IBS-D showed a stronger association of pain with changes in stool consistency (70% vs. 60% of time with pain, p<0.001) and frequency (mean 61.3% vs. 57.8% of time with pain, p=0.008). These associations remained significant in multiple regression models, which confirmed that IBS-C is more strongly linked to prolonged and escalating pain episodes, while IBS-D is more closely linked to pain associated with changes in stool frequency and consistency. As compared to FD, IBS-D patients reported greater dissatisfaction with bowel function (57.3±28.4 vs. 44.2±29.8, p<0.001), and more frequent loose stools (without constipation treatments) (60.0% vs. 50.0% of bowel movements, p<0.001), particularly after meals (60.0% vs. 40.0% of loose stools, p<0.001). IBS-C shows more severe constipation-related symptoms compared to FC (p<0.001). Mediation analyses revealed that concerns about bowel function, embarrassment discussing it, and work-related impairments partially mediated the relationship between IBS and psychological distress.

Conclusion

IBS-C is associated with more severe pain episodes, including prolonged and escalating pain, while in IBS-D pain is more strongly linked to bowel habit changes. These findings highlight the distinct clinical profiles of IBS subtypes and emphasize the need for personalized, multimodal management strategies. Identifying mediators of psychological distress in IBS can guide targeted interventions, improving patient outcomes.

References

1. Lacy, B. E. et al. Bowel Disorders. Gastroenterology (2016) doi:10.1053/j.gastro.2016.02.031.
2. Savarino, E. et al. Functional bowel disorders with diarrhoea: Clinical guidelines of the United European Gastroenterology and European Society for Neurogastroenterology and Motility. United European Gastroenterol J 10, 556–584 (2022).
3. Mearin, F. et al. Clinical Practice Guideline: Irritable bowel syndrome with constipation and functional constipation in the adult. Revista espanola de enfermedades digestivas 108, 332–63 (2016).
4. Baron, R. M. & Kenny, D. A. The moderator-mediator variable distinction in social psychological research: conceptual, strategic, and statistical considerations. J Pers Soc Psychol 51, 1173–82 (1986).