Objectives: To evaluate the responsiveness of composite scales to change over time in a clinical trial of patients with interstitial cystitis (IC). The measurement of symptoms in IC includes the O'Leary-Sant Symptom and Problem Indexes and the University of Wisconsin Interstitial Cystitis Inventory and scales that measure the individual symptom domains of pain/discomfort, urgency, and voiding frequency.
Methods: The data were derived from a randomized clinical trial conducted by the Interstitial Cystitis Clinical Trials Group. Participants met the National Institutes of Health-National Institute for Diabetes, and Digestive and Kidney Diseases criteria for IC and reported at least moderate pain and frequency. The primary endpoint was a patient-reported global response assessment (GRA) at 24 weeks. Secondary endpoints included the three composite indexes, pain/discomfort and urgency, and 24-hour frequency. Responsiveness was assessed by comparing symptom score changes against response categories defined by the GRA.
Results: Of the 121 subjects in the original trial, 94 with complete data were included. All three composite indexes were sensitive to subject improvement over time as measured by the GRA. A 1.2-point change in the O'Leary-Sant indexes and a 3.1-point change in the Wisconsin IC inventory corresponded to a one-category change in the GRA. Individual symptoms were also responsive. The correlation was high among the changes in the six outcome measures.
Conclusions: The three composite symptom scales are responsive to change over time in patients with IC. These indexes provide important insight into symptom changes and are recommended as secondary endpoints in future clinical trials of IC. Additional endpoints addressing individual symptom domains should also be considered to aid in the evaluation of effect mechanisms.