Pelvic floor distress inventory 20 and Wexner constipation scoring system responsiveness and minimal clinical importance difference in Persian women with functional constipation

Functional constipation disproportionately affects women and impairs quality of life. Patient-reported outcome measures (PROMs) like the Wexner Constipation Scoring System (WCSS) and Pelvic Floor Distress Inventory-20 (PFDI-20) are widely recommended in clinical and research settings. However, responsiveness and minimal clinically important difference (MCID) after physiotherapy have not been validated in Persian speakers. This study aimed to evaluate these properties. In this longitudinal study, 66 women with diagnosed functional constipation underwent 10 standardized physiotherapy sessions (including electrotherapy, biofeedback, and therapeutic exercises) over 4–6 weeks. Internal responsiveness was assessed using Cohen’s d and Standardized Response Mean (SRM), while external responsiveness was evaluated using Spearman’s correlation (against the Global Rating of Change Scale [GRCS]) and covariate-adjusted receiver operating curve (ROC) regression analysis. Covariate-adjusted MCID thresholds were calculated using anchor-based methods. The WCSS questionnaire demonstrated excellent internal responsiveness (Cohen’s d = -2.05 and SRM = -2.71), excellent external responsiveness (Spearman correlation coefficient = -0.715), and outstanding discriminative ability (area under the ROC curve = 0.94) in patients with functional constipation following 4–6 weeks of routine physiotherapy. The MCID for this questionnaire was 4 points, with a sensitivity and specificity of 0.88. Additionally, the PFDI-20 questionnaire showed excellent internal responsiveness (Cohen’s d = -1.19 and SRM = -1.42), poor external responsiveness (Spearman correlation coefficient = -0.485), and excellent discriminative ability (area under the ROC curve = 0.83) following 4–6 weeks of routine physiotherapy for functional constipation. Its MCID was 27.09 points, with a sensitivity of 0.82 and specificity of 0.70. Among the three subscales of PFDI-20, the Colorectal Anal Distress Inventory (CRADI) exhibited better responsiveness compare to others, with Cohen’s d = -1.45 and SRM = -0.77, Spearman correlation coefficient = -0.594 and area under the ROC curve = 0.87. WCSS demonstrated greater responsiveness and sensitivity than PFDI-20 for assessing improvement after physiotherapy in patients with functional constipation. The PFDI-20 remains valuable for comprehensive pelvic floor evaluation, and its CRADI subscale can serve as a complementary tool for tracking colorectal symptoms.