Minimal clinically important differences in Incontinence Quality-of-Life scores in stress urinary incontinence

To determine the clinically relevant reference points for the Incontinence Quality of Life (I-QOL) questionnaire scores in women with stress urinary incontinence and compare them with the treatment effects observed with duloxetine and placebo. Using data from 1133 women with predominant stress urinary incontinence in two randomized, placebo-controlled duloxetine studies, the within-treatment and between-treatment minimal clinically important differences (MCIDs) were obtained by anchoring the I-QOL scores to the validated Patient Global Impression of Improvement scale (PGI-I). The within-treatment MCID (mean I-QOL for women rating their condition “a little better” with treatment) and between-treatment MCID (difference in scores between the group ratings of “no change” and “a little better”) were derived. The treatment effects were compared with these MCIDs. Real-time urinary diaries were completed, along with the I-QOL and PGI-I. The within-treatment and between-treatment MCID for the I-QOL total score was 6.3 and 2.5, respectively. The total and subscale scores had almost identical MCIDs. Duloxetine 80 mg significantly improved the I-QOL total and subscale scores. Treatment differences in the I-QOL scores exceeded the between-treatment MCID and the duloxetine I-QOL treatment effect exceeded the within-treatment MCID. The number of patients needed to treat to gain an additional I-QOL responder was 6.8. Improvements in I-QOL scores should be greater than the within-treatment MCID, and differences between two treatments should be greater than the between-treatment MCIDs, for statistically significant differences to be considered clinically meaningful. We propose 2.5 points as a reasonable guide for the I-QOL between-treatment MCID and 6.3 points for the within-treatment MCID.