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 r 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.