Small intestinal permeability is frequently abnormal in diarrhea-predominant IBS. Those without a history of infectious onset appear to have a more severe defect.

SUMMARY BackgroundAnxiety, depression and nongastrointestinal symptoms are often prominent in irritable bowel syndrome (IBS), but their relative value in patient management has not been quantitatively assessed. We modified the Patient Health Questionnaire 15 (PHQ-15) by excluding three gastrointestinal items to create the PHQ-12 Somatic Symptom (PHQ-12 SS) scale.

IBS-D and PI-IBS patients are associated with TNFSF15 and TNFα genetic polymorphisms which also predispose to Crohn's disease suggesting possible common underlying pathogenesis.

The study of post-infectious irritable bowel syndrome has revealed the importance of low-grade inflammation in causing irritable bowel syndrome symptoms. It has suggested novel approaches to irritable bowel syndrome including studies of serotonin and histamine metabolism which may be relevant to other subtypes of the disease.