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

Abstract

Objectives: 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.

Methods: 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.

Results: 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.

Conclusions: 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.