Defining a minimal clinically important difference for endometriosis-associated pelvic pain measured on a visual analog
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RESEARCH
Open Access
Defining a minimal clinically important difference for endometriosis-associated pelvic pain measured on a visual analog scale: analyses of two placebo-controlled, randomized trials Christoph Gerlinger1*, Ulrike Schumacher2, Thomas Faustmann3, Antje Colligs4, Heinz Schmitz5, Christian Seitz5
Abstract Background: When comparing active treatments, a non-inferiority (or one-sided equivalence) study design is often used. This design requires the definition of a non-inferiority margin, the threshold value of clinical relevance. In recent studies, a non-inferiority margin of 15 mm has been used for the change in endometriosis-associated pelvic pain (EAPP) on a visual analog scale (VAS). However, this value was derived from other chronic painful conditions and its validation in EAPP was lacking. Methods: Data were analyzed from two placebo-controlled studies of active treatments in endometriosis, including 281 patients with laparoscopically-confirmed endometriosis and moderate-to-severe EAPP. Patients recorded EAPP on a VAS at baseline and the end of treatment. Patients also assessed their satisfaction with treatment on a modified Clinical Global Impression scale. Changes in VAS score were compared with patients’ selfassessments to derive an empirically validated non-inferiority margin. This anchor-based value was compared to a non-inferiority margin derived using the conventional half standard deviation rule for minimal clinically important difference (MCID) in patient-reported outcomes. Results: Anchor-based and distribution-based MCIDs were-7.8 mm and-8.6 mm, respectively. Conclusions: An empirically validated non-inferiority margin of 10 mm for EAPP measured on a VAS is appropriate to compare treatments in endometriosis.
Introduction Endometriosis is a common condition in women of reproductive age that is characterized by the presence of functional endometrium-like tissue outside the uterus (e.g., the ovaries and other pelvic structures). Changes in the number and size of such endometriotic lesions were often used to assess the efficacy of treatment options for endometriosis [1-4]. However, there is no direct correlation between the extent of these lesions and the severity of the symptoms experienced by the patient [5-7]. Potential explanations for this lack of correlation are that the level of pain induced by endometriosis might be determined by the depth of tissue * Correspondence: [email protected] 1 Global Clinical Statistics, Bayer Schering Pharma AG, 13342 Berlin, Germany Full list of author information is available at the end of the article
intrusion of a specific lesion, or that there may be a direct interaction of endometriotic lesions and nerve fibers [8,9]. Neither of these potential explanations can be assessed by visual inspection during surgery and are therefore not reflected in the respective scoring systems for endometriosis severity [10,11]. Typical symptoms of endometriosis include dysmenorrhea, dyspareunia, and chronic pelvic pain [12-14]. Pain is commonly consid
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