Minimally Important Difference for Patient-reported Outcomes in Psoriatic Arthritis: Health Assessment Questionnaire and Pain, Fatigue, and Global Visual Analog Scales

Objective. To determine the minimally important difference (MID) for the Health Assessment Questionnaire-Disability Index (HAQ-DI), pain, fatigue, sleep, and global visual analog scale (VAS; 0-100 mm) in patients with psoriatic arthritis (PsA) using a patient-reported overall health status anchor. Patient-reported outcomes are often used to gauge the effect of PsA in clinical trials. There is currently no knowledge about the MID for patient-reported outcomes in PsA. Methods. Patients with a diagnosis of PsA who had answered questions about outcomes at 2 consecutive visits and an overall health status question (How would you describe your overall status since your last visit: much better, better, the same, worse, much worse?) were included. MID was calculated as the mean change between visits for those who rated their disease as better or worse. Results. Two hundred patients met inclusion criteria, of whom 17.5% rated their status as better and 25.0% rated their status as worse than the previous visit. MID estimates for improvement/worsening (SD) respectively were -0.131 (0.411)/0.131 (0.309) for HAQ-DI, -9.37 (24.37)/13.96 (22.05) for pain VAS, -8.15 (23.52)/3.63 (27.62) for fatigue VAS, -10.97 (29.74)/13.81 (27.32) for sleep VAS, and -8.41 (21.17)/11.53 (21.03) for global VAS. Spearman's p correlation coefficients between the anchor and mean change were 0.374 (HAQ-DI), 0.448 (pain VAS), 0.239 (fatigue VAS), 0.326 (sleep VAS), 0.490 (global VAS); p<0.01. Conclusion. This is the first study investigating MID of patient-reported outcomes in PsA. MID for HAQ-DI, pain, and global VAS were shown to be the best predictors for a patient's perception of overall changes in disease status. (First Release March 15 2010; J Rheumatol 2010:37:1024-8: doi:10.3899/jrheum.090832)