Objectives: The objectives of this study were to determine how variable stool consistency is in patients with irritable bowel syndrome (IBS) and to assess the relationship between stool consistency and gastrointestinal symptoms.
Methods: Individuals with a physician diagnosis of IBS were recruited by advertisement. Enrollment questionnaires included the Rome III Diagnostic Questionnaire and IBS Symptom Severity Scale. Then, 185 patients meeting the Rome criteria for IBS rated the consistency (using the Bristol Stool Scale) of each bowel movement (BM) for 90 days and whether the BM was accompanied by pain, urgency, or soiling. Each night, they transferred BM ratings from a paper diary to an internet form and also reported the average daily intensity of abdominal pain, bloating, bowel habit dissatisfaction, and life interference of bowel symptoms. Only the longest sequence of consecutive days of diary data was used in the analysis (average of 73 days).
Results: Patients were 89% females with average age 36.6 years. Among the patients, 78% had both loose/watery and hard/lumpy stools; the average was three fluctuations between these extremes per month. The proportion of loose/watery stools correlated r=0.78 between the first and second months and the proportion of hard/lumpy stools correlated r=0.85 between months. Loose/watery stools were associated with more BM-related pain, urgency, and soiling than hard/lumpy or normal stools; however, IBS-C patients had significantly more BM-unrelated abdominal pain, bloating, dissatisfaction with bowel habits, and life interference than IBS-D patients. Questionnaires overestimated the frequency of abnormal stool consistency and gastrointestinal symptoms compared with diaries.
Conclusions: Stool consistency varies greatly within individuals. However, stool patterns are stable within an individual from month to month. The paradoxical findings of greater symptom severity after individual loose/watery BMs vs. greater overall symptom severity in IBS-C implies different physiological mechanisms for symptoms in constipation compared with diarrhea. Daily symptom monitoring is more sensitive and reliable than a questionnaire.