Gastrointestinal and psychological mediators of health-related quality of life in IBS and IBD: a structural equation modeling analysis

Abstract

Objectives: 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.

Figure 1

Health-related quality of life (HRQOL) for inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). A single construct of HRQOL was composed of four subscales of the SF-36: physical functioning, role functioning, social functioning, and role emotional. Numeric values of these four subscales are shown as 0.60, 0.83, 0.55, and 0.74, all statistically significant factor loadings. el-e4 denote error variances that were moderately correlated, suggesting the presence of some shared method variance. Df, degrees of freedom; NFI, normed fit index.

Figure 2

Final model of structural relationship of gastrointestinal (GI) symptoms, psychological distress, and health-related quality of life (HRQOL) in irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) denoted by ovals. Specific GI symptoms, individual psychological distress symptoms, and four subscales of the SF-36 are represented in boxes. The values on the paths are regression coefficients representing the impact of one variable on another. Each of the coefficients are significant to the P<0.0001 level and have been standardized to facilitate relative interpretations. Numeric values in parenthesis refer to the IBD sample, whereas others are for IBS. Negative coefficients between the symptom and HRQOL variables reflect the reversed scaling of HRQOL (greater values represent greater well-being). Df, degrees of freedom; NFI, normed-fit index.