Patient-Reported Outcomes for Irritable Bowel Syndrome Are Associated With Patients' Severity Ratings of Gastrointestinal Symptoms and Psychological Factors

BACKGROUND & AIMS: Patient-reported outcomes (PROs) are used to gauge the benefit of treatments for functional gastrointestinal disorders, including irritable bowel syndrome (IBS). Commonly used end points derived from scales of symptom severity differ in their structure, format, and the extent to which they are based on established psychometric fundamentals. We evaluated the overlap between 2 measures of IBS symptom severity, documented their association with different symptoms (pain, bloating, altered defecation), and identified psychological factors that might bias PRO ratings, by affecting how patients interpret IBS symptom severity. METHODS: Ninety-eight patients diagnosed with IBS, based on Rome III criteria, completed the multicomponent IBS Symptom Severity Scale and the single-item, UCLA Symptom Severity Scale. Data were collected on pain, bloating, and bowel habits, as well as somatization, sensitivity to arousal symptoms (anxiety sensitivity), and a negative thinking style called pain catastrophizing. RESULTS: The 2 global scales were correlated with one another (r = 0.56); each scale was associated most strongly with variation in abdominal pain. Data were consistent with a model in which pain catastrophizing and somatization influenced 1 or more of patients' judgments of pain, bloating, and/or bowel habits, which then affected the PROs. CONCLUSIONS: Depending on their structure and format, PROs can have different levels of sensitivity to core IBS symptoms and be influenced by psychological and somatic complaints that are beyond the aim of therapy and labeling claim. PROs that rely on patients' perspectives to index symptom severity can be improved by consideration of psychometric principles that influence self-report.