The minimally important difference for patient reported outcomes in systemic lupus erythematosus including the HAQ-DI, pain, fatigue, and SF-36

Abstract

Objective: We studied patients with systemic lupus erythematosus (SLE) in 1 clinical practice, and patients enrolled in the 1000 Canadian Faces of Lupus database, to determine the minimally important difference (MID) for pain, fatigue, sleep, Health Assessment Questionnaire-Disability Index (HAQ-DI), and Medical Outcomes Study Short Form-36 (SF-36) Physical Component Score (PCS) and SF-36 Mental Component Score (MCS) using a patient-reported overall health status anchor.

Methods: Patients with SLE who had 2 consecutive clinic visits and completed a HAQ-DI and a pain, fatigue, and sleep visual analog scale (VAS) (0-100), and an overall health status question: "How would you describe your overall status since your last visit?": much better, better, the same, worse, or much worse were included. Those who self-rated as better or worse were considered the "minimally changed" subgroups. Patients with 2 consecutive annual visits in the 1000 Canadian Faces of Lupus database who completed the SF-36 and health transition question were eligible.

Results: There were 202 patients in London, Ontario (94% women, mean age 50 yrs, mean disease duration 10 yrs). MID for better and worse on a VAS (0-100) were: pain (-15.8, 8.5), fatigue (-13.9, 9.1), and sleep problems (-8.6, 7.6). The MID for HAQ-DI (scale 0 to 3) was -0.08 (better) and 0.14 (worse). The MID for SF-36 was 2.1 (better) and -2.2 (worse) for the PCS and 2.4 (better) and -1.2 (worse) in the MCS.

Conclusion: The MID in patients with SLE may be different bidirectionally depending on the measured outcome. The mean change observed for those reporting better than worse outcome in pain and fatigue was greater for better versus worst, in contrast to the HAQ, where the mean change was greater for worsening.