The evolution of irritable bowel syndrome as a group of organic diseases: a narrative review

Historically, irritable bowel syndrome (IBS) has been classified as a functional disorder, diagnosed through symptom-based criteria and managed by a uniform algorithm. However, current research suggests IBS may represent a group of disorders, each with an organic basis, such as post-infectious changes to the intestinal tract, inflammation, and immune activation, gut-brain axis dysfunction, bile acid dysregulation, or gut microbiome irregularities.

This literature review examines the historical classification of IBS, the revisions/changes in diagnostic criteria over time, and innovative research into potential causes of the disease. Key advances including bile acid profiling, stool microbiome analysis, mast cell markers, and breath testing are explored. Additionally, emerging treatments targeting these mechanisms are reviewed. These include microbiome-directed therapies, including antibiotics, probiotics, anti-inflammatory agents, and bile acid modulators. The literature search included peer-reviewed studies, clinical trials, and meta-analyses from major medical databases.

Although existing symptom-based diagnostic criteria for IBS have been useful, they have contributed to a situation whereby current treatments address symptoms, not the underlying causes. Approaching IBS as a constellation of diseases with individual organic bases will allow the development of more precisely targeted and effective treatments.