Testing the sequential model of pain processing in irritable bowel syndrome: a structural equation modeling analysis

Pain, the cardinal feature of irritable bowel syndrome (IBS), is a multidimensional phenomenon with sensory and affective dimensions. Price's [Psychological Mechanisms of Pain and Analgesia, 1999] pain processing model was used to delineate four a priori sequentially related stages (pain sensation intensity, immediate pain unpleasantness, long-term suffering, and pain-related behavior). Although prior research with both healthy individuals and somatic pain patients supports the model in general, its applicability to IBS is unclear. Our goal was to extend the scope of the sequential model and test its fundamental tenets using structural equation modeling (SEM) with data obtained from 168 Rome II diagnosed IBS patients (19% male, 81% female). A secondary goal was to assess the relationship between a set of contextual factors associated with IBS (age, gender, trait anxiety) and the four pain stages. Results were consistent with a successive order of pain processing such that the pain sensation directly impacts pain unpleasantness, which, in turn, leads to suffering and illness behaviors. However, contrary to a model with strictly successive stages, pain sensation had independent effects on illness behaviors over and above pain affect. The effect of anxiety on illness behavior was mediated by suffering, while psychopathology directly influenced pain sensation and pain unpleasantness but not later stages. Age was related to pain sensation and illness behaviors but not pain affect. Gender tended to be more strongly associated with more distal pain stages (e.g., pain affect) vis-à-vis its effects on pain sensation. These data are generally supportive of a four-stage pain processing model.