Characterization of symptoms in irritable bowel syndrome with mixed bowel habit pattern

Background: Irritable bowel syndrome (IBS) with mixed bowel habits (IBS-M) is a heterogeneous subtype with varying symptoms of constipation and diarrhea, and has not been well characterized. We aimed to characterize gastrointestinal (GI) and non-GI symptoms in IBS-M patients from a US patient population, and to compare them with IBS with constipation (IBS-C) and diarrhea (IBS-D). Methods: Subjects answering community advertisements and meeting Rome III criteria for IBS completed symptom questionnaires. Key Results: Of the initial 289 IBS patients identified, one third (n = 51, 32.5%) who met Rome III criteria for IBS-M endorsed having either loose stools or hard stools due to medication. These patients had more severe symptoms and longer duration of flares compared to the rest of the IBS-M group (p = 0.014, p = 0.005). Excluding IBS-M patients with medication-related extremes in stool form who could not be reclassified by medical history, 247 IBS patients were assessed. IBS-M was the most common (44.1%), followed by IBS-C (27.9%), IBS-D (26.3%), and IBS-U (unsubtyped, 1.6%). While IBS-M shared symptoms with both IBS-C and IBS-D, there were significant differences in the prevalence of bowel habit symptoms (p-value range: <0.001-0.002). IBS-M patients reported most bothersome symptoms that were more similar to IBS-D, with the most common being irregular bowel habits (27.5%), bloating (26.6%), and abdominal pain (20.2%). There were no differences in non-GI symptoms between subtypes. Conclusions & Inferences: IBS-M is a heterogeneous symptom group and thus requires that subclassification criteria be better defined. Use of laxative/antidiarrheal medications adds to the diagnostic complexity in a potentially more severe subset of IBS-M and should be assessed for accurate subclassification.