Objective Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are chronic gastrointestinal (GI) syndromes in which both GI and psychological symptoms have been shown to negatively impact health-related quality of life (HRQOL). The objective of this study was to use structural equation modeling (SEM) to characterize the interrelationships among HRQOL, GI, and psychological symptoms to improve our understanding of the illness processes in both conditions. Methods Study participants included 564 Rome positive IBS patients and 126 IBD patients diagnosed via endoscopic and / or tissue confirmation. All patients completed questionnaires to assess bowel symptoms, psychological symptoms (SCL-90R), and HRQOL (SF-36). SEM with its two components of confirmatory analyses and structural modeling were applied to determine the relationships between GI and psychological symptoms and HRQOL within the IBS and IBD groups. Results For both IBD and IBS, psychological distress was found to have a stronger direct effect on HRQOL(−0.51 and −0.48 for IBS and IBD, respectively) than GI symptoms (−0.25 and −0.28). The impact of GI symptoms on psychological distress was stronger in IBD compared with IBS (0.43 vs. 0.22; P <0.05). The indirect effect of GI symptoms on HRQOL operating through psychological distress was significantly higher in IBD than IBS (−0.21 vs. −0.11; P <0.05). Conclusions Psychological distress is less dependent on GI symptom severity in IBS compared with IBD even though the degree that psychological distress impacts HRQOL is similar. The findings emphasize the importance of addressing psychological symptoms in both syndromes.

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