Factor Analysis Demonstrates a Symptom Cluster Related to Methane and Non-methane Production in Irritable Bowel Syndrome

Introduction: Irritable bowel syndrome (IBS) is a chronic disorder often subdivided into constipation-predominant and diarrhea-predominant forms. Earlier studies have shown that IBS patients with methane detected on lactulose breath test (LBT) are more likely to have constipation. The goal of this study was to conduct a factor analysis to determine whether there is a cluster of symptoms associated with methane production. Methods: Patients with IBS referred for a LBT completed a questionnaire assessing 31 symptoms. The degree of each symptom was graded on a visual analog scale of 0 to 5. Exploratory factor analysis was carried out separately in methane and nonmethane patients. A score was determined for each symptom cluster by summing across the related variables. The cluster scores were compared between the 2 groups by the Wilcoxon rank-sum test. Results: A total of 459 IBS patients (72 with methane, 387 with nonmethane) were evaluated. On the basis of factor analysis results, 3 symptom clusters (bloating weighted, pain weighted, and constipation weighted) were created in methane-producing patients. Two symptom clusters (bloating weighted and diarrhea weighted) were created in the nonmethane group. The groups did not differ significantly on the methane-derived bloating score (P = 0.24) or the pain score (P = 0.15). However, the methanederived constipation score was significantly higher in the methane group, 15.3 +/- 4.9 versus 13.4 +/- 4.9, P = 0.002. The constipationweighted cluster included the following symptoms: constipation, lack of milk intolerance, lack of weight loss, small bowel movements, and straining. The diarrhea cluster score was significantly higher in the nonmethane group, 14.2 +/- 8.0 versus 11.3 +/- 6.5, P = 0.005. The diarrhea cluster included the following symptoms: diarrhea, pain with bowel movements, pain after bowel movements, foul-smelling bowel movements, and large bowel movements. The groups did not differ significantly on the nonmethane-derived bloating cluster, P = 0.11. Conclusions: Methane-producing IBS patients have a unique cluster of symptoms related to constipation.