Minimal important change in the pelvic floor distress inventory-20 among women opting for conservative prolapse treatment

Abstract

The Pelvic Floor Distress Inventory-20 is used to evaluate symptoms and treatment effects in women with pelvic floor disorders. To interpret changes in the scores of this inventory, information is needed about what patients and clinicians perceive as the minimal important (meaningful) change. Although this change in the inventory score has been investigated previously in women who have undergone pelvic floor surgery, the results could not be generalized to women with milder symptoms (ie, lower scores) who often require only conservative treatment. We aimed to estimate the minimal important change in the Pelvic Floor Distress Inventory-20 that was needed to demonstrate clinical improvement in women who qualify for conservative pelvic floor treatment. The data of 214 women aged ≥55 years were used. All participants were from 2 randomized controlled trials that compared conservative prolapse treatments in primary care in The Netherlands. The degree of prolapse was assessed with the use of the Pelvic Organ Prolapse Quantification system; participants completed the Pelvic Floor Distress Inventory-20 at baseline and at 12 months, with a global perception of improvement question at 12 months. To assess both the patient perspective and the clinical perspective, 2 anchors were assessed: (1) the global perception of improvement was considered the anchor for the patients' perspective, and (2) the difference in the degree of prolapse was considered the anchor for the clinical perspective. Provided that the anchors were correlated by at least 0.3 to the Pelvic Floor Distress Inventory-20 change scores, we estimated the following minimal important changes: (1) the optimal cutoff-point of the receiver operating characteristics curve that discriminates between women with and without improvement in the global perception of improvement scale and (2) the mean Pelvic Floor Distress Inventory-20 change score of participants who improved 1 assessment stage. We then calculated the smallest detectable change to check whether the minimal important change was larger than the measurement error of the questionnaire. Using the global perception of improvement as the anchor, we found a minimal important change for improvement of 13.5 points (95% confidence interval, 6.2-20.9). The Pelvic Organ Prolapse Quantification change scores correlated poorly to the Pelvic Floor Distress Inventory-20 change scores and therefore could not be used as an anchor. The smallest detectable change at the group level was 5.5 points. Thus, the minimal important change was larger than the smallest detectable change at the group level. In women with relatively mild pelvic floor symptoms, an improvement of 13.5 points (or a 23% reduction) in the Pelvic Floor Distress Inventory-20 score can be considered clinically relevant. This minimal important change can be used for clinical trial planning and evaluation of treatment effects in women whose condition is considered suitable for conservative treatment.