Symptom Severity in Functional Bowel Disorders is Determined by Psychological Profile, Traumatic Events and Stress Reactivity

Background: IBS is a common, painful, potentially disabling GI disorder associated with significant mental and medical (physical) comorbidity.The rate of mental-physical comorbidity is particularly high in more severe IBS patients seen in tertiary care settings.The individual and joint effects of coexisting mental and physical conditions on IBS is unknown but important because of their influence on health outcomes in general.Aim.This study investigated the explanatory value of 2 approaches for modeling mental-physical comorbidity associated with IBS.The additive model conceptualizes comorbidity as the co-occurrence of the number (#) of coexisting mental and physical health conditions (A + B).The interaction model suggests that the # of mental comorbidities interacts synergistically with physical ones (A x B) to affect IBS outcomes.Design: 133 Rome III-diagnosed IBS pts (M age = 39 yrs, 77% F, 91% C) completed baseline assessment of an NIH-funded RCT.Mental comorbidity was assessed using the MINI Neuropsychiatric Diagnostic Interview, a structured assessment of Axis I DSM-IV psychiatric disorders.Physical comorbidity was assessed with the Medical Comorbidity Questionnaire, a self administered measure requiring pts to identify whether they have received a formal medical diagnosis of 100 defined medical conditions and, if so, to rate the current (past 3 months)severity of each disease on a 5-point scale (1= absent, 5=very severe).Dependent variables included the IBS Symptom Severity Scale (IBS-SSS), IBS Quality of Life (IBSQOL), Brief Symptom Inventory-18 (BSI-18; emotional distress), and McGill Pain Inventory (MPI).Results.Additive and interaction multiple regression models were compared for each outcome variable.The additive model accounted for 5% of the variance in the IBS-SSS; 10% of the variance in the MPI; 14% of the variance in the IBSQOL; and 53% of the variance in the BSI-18.The number of mental, but not physical, comorbidities was a significant predictor of the IBS-SSS and MPI (p < .05).The total number of mental and physical comorbidities were significant predictors of the IBSQOL and BSI-18.The interaction model (# of mental X # of physical comorbidities) accounted for 6% of the variance in the IBS-SSS; 11% of the variance in the MPI; 21% of the variance in the IBSQOL; and 55% of the variance in the BSI-18.The only outcome variable for which the interaction of mental and physical comorbidities accounted for a significant amount of unique variance was the IBSQOL.Conclusion.For 3 out of the 4 outcome variables presented, the additive model appears sufficient.An interaction model added a significant amount of unique variance for the IBSQOL.The number of mental comorbidities appears more strongly related to IBS outcomes than the number of physical comorbidities.