Clinically important improvement in the WOMAC and predictor factors for response to non-specific non-steroidal anti-inflammatory drugs in osteoarthritic patients: A prospective study

Background: The aims of the present study were first to detect MCID for WOMAC in a Moroccan population, and second, to identify the best pre-treatment predictors on the change of health after treatment by non-specific, non-steroidal anti-inflammatory drugs (NSAIDs), and to evaluate whether the predictors were dependent on the choice of the response criterion. Methods. The study involved 173 patients with osteoarthritis in whom primary care physicians decided to start treatment with non-selective NSAIDs. Assessments at admission and after 6 weeks were conducted. In order to determine the threshold levels associated with a definition of clinically important improvement, the receiver operating characteristic method was used. Three different measures of response to a 6-week NSAIDs treatment were used: one indirect measure (MCID in the total WOMAC score), one direct measure (transition question) and a combination of both criteria. Results: Eighty patients (46.3%) reported "a slightly better" general health status compared to that of 6 weeks before NSAIDs treatment. The MCID proportion is a 16.0% reduction in WOMAC. The most stable pre-treatment predictors on the improvement of health after treatment by NSAIDs were the absence of previous knee injury and a high level of education. Conclusions: In our data, a 16.0% reduction of the total WOMAC score from baseline was associated with the highest degree of improvement on the transition scale category. This cut-off point had good accuracy, and should be appropriate for use in the interpretation of clinical studies results, as well as in clinical care. © 2012 Hmamouchi et al; licensee BioMed Central Ltd.