The Minimally Important Difference for Patient-reported Outcomes in Spondyloarthropathies including Pain, Fatigue, Sleep, and Health Assessment Questionnaire

Abstract

To study minimal important differences (MID) in spondyloarthropathies (SpA). MID are important in determining clinically relevant changes and for interpretation of trials and treating patients. MID have been widely studied in rheumatoid arthritis, but less so in SpA. Patients with SpA had to be seen for 2 consecutive visits and have completed the Health Assessment Questionnaire (HAQ) and 100 mm visual analog scale on both visits for fatigue, pain, sleep, and global assessment. At the second visit they had to answer a question regarding any change in their overall health (from last visit), responding with much better, better, same, worse, or much worse. The MID were the mean changes for those who were either better or worse. Our study involved 140 eligible patients with a SpA: 69% were men, the mean age was 45 years, and the mean disease duration was 14.5 years. Almost half the patients rated themselves as unchanged from the previous visit but the remainder were either better or worse, with a minority rating themselves as much better or much worse. The MID for better and worse outcomes were HAQ (-0.136; 0.220), pain (-6.93; 18.97), fatigue (-1.43; 14.42), and sleep (-2.23; 10.76). No gender differences were observed. Our results demonstrate that the MID vary depending on better versus worse (bidirectionally different). MID may be smaller in clinical practice than what is observed in trials.