Objectives: The Rome III classification system treats functional constipation (FC) and irritable bowel syndrome with constipation (IBS-C) as distinct disorders, but this distinction appears artificial, and the same drugs are used to treat both. This study's hypothesis is that FC and IBS-C defined by Rome III are not distinct entities.
Methods: In all, 1,100 adults with a primary care visit for constipation and 1,700 age- and gender-matched controls from a health maintenance organization completed surveys 12 months apart; 66.2% returned the first questionnaire. Rome III criteria identified 231 with FC and 201 with IBS-C. The second survey was completed by 195 of the FC and 141 of the IBS-C cohorts. Both surveys assessed the severity of constipation and IBS, quality of life (QOL), and psychological distress.
Results: (i) Overlap: if the Rome III requirement that patients meeting criteria for IBS cannot be diagnosed with FC is suspended, 89.5% of IBS-C cases meet criteria for FC and 43.8% of FC patients fulfill criteria for IBS-C. (ii) No qualitative differences between FC and IBS-C: 44.8% of FC patients report abdominal pain, and paradoxically IBS-C patients have more constipation symptoms than FC. (iii) Switching between diagnoses: by 12 months, 1/3 of FC transition to IBS-C and 1/3 of IBS-C change to FC.
Conclusions: Patients identified by Rome III criteria for FC and IBS-C are not distinct groups. Revisions to the Rome III criteria, possibly including incorporation of physiological tests of transit and pelvic floor function, are needed.