Patient-Reported Outcomes in Assessing IBS Severity

Orlando—Characterizing the therapeutic benefit of novel agents for irritable bowel syndrome relies heavily on patient-reported outcomes (PROs) assessing multiple gastrointestinal symptoms. Common approaches that sum or average responses across various components of the illness must be unidimensional and have small unique as opposed to common variance to avoid aggregation bias and misrepresentation of clinical data.

During a poster session at DDW 2013, researchers reported results of a study designed to evaluate the unidimensionality of the IBS Symptom Severity Scale (IBS-SSS), identify meaningful patterns of multiple symptoms, and determine the relationships between these symptom patterns and psychosocial factors possibly influencing treatment response to novel agents. The poster was titled IBS Symptom Severity Subtypes and Their Relationship with Psychosocial Factors: Improving the Sensitivity and Meaning of Patient-Reported Outcomes.

The researchers analyzed data generated by 239 Rome-diagnosed IBS patients who completed the 5-item IBS-SSS as well as various psychological tests. Factor analyses showed that the IBS-SSS was not unidimensional; latent profile analysis revealed 4 common symptom profiles for items comprising the IBS-SSS.

Cluster 1 (45%) had relatively low scores on all dimensions with the exception of bowel dissatisfaction and life interference associated with IBS symptoms; cluster 2 (25%) had elevated life dissatisfaction and life interference; cluster 3 (19%) had high frequency of pain and life interference; and cluster 4 (10%) had high frequency, but low severity, of pain and moderate life interference.

In summary, the authors said, “The IBS-SSS is not unidimensional. PRO development relying on multicomponent assessments of symptom severity should consider the multidimensional structure of symptoms to avoid aggregation bias and to optimize the sensitivity of detecting treatment effects. IBS patients can be grouped into 4 symptom clusters on the basis of their responses to individual items on the IBS-SSS.”