Objectives: Many fecal incontinence (FI) studies define primary efficacy outcome as a decrease from baseline of ≥ 50% in the number of FI episodes; this threshold has never been validated. We aimed to establish the validity and responsiveness of ≥ 50% reduction in FI episodes (responder50) as the threshold indicative of clinically meaningful response. Methods: Adults with a Cleveland Clinic Florida fecal incontinence score ≥ 10 were randomized to receive nonanimal stabilized hyaluronic acid/dextranomer (NASHA/Dx) injection or sham treatment in a 6-month trial. Validity and responsiveness of the primary end point were evaluated post hoc. The data were compared using different thresholds for defining a responder for a number of end points. Results: Data from 206 patients (NASHA/Dx, n=136; sham, n=70) were evaluated. Incremental patient response threshold increases showed that although the percentage of patients who achieved response decreased with increasing threshold, the difference between treatments remained significant up to an 80% response threshold (NASHA/Dx, 23%; sham, 10%; P=0.02). Response thresholds between 40% and 80% demonstrated evidence for convergent validity, with the strongest correlation with the number of FI episodes, the number of FI episodes when the patient was awake, and the number of FI-free days observed at ≥ 40% and ≥ 50% thresholds. Further examination of the responder50 threshold indicated that, regardless of treatment (NASHA/Dx or sham), responders performed significantly better than nonresponders on nearly all secondary efficacy end points. Conclusion: This study demonstrates the responsiveness, validity, and clinical applicability of the ≥ 50% response threshold in clinical studies of patients with FI receiving treatment with NASHA/Dx.
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