Assessment of the minimal clinically important difference for the Health Assessment Questionnaire Disability Index in patients with arthralgia at risk for progression to rheumatoid arthritis.

Introduction: Patients with arthralgia at-risk for rheumatoid arthritis (RA) experience considerable functional disability, though generally less than at RA diagnosis. Secondary prevention trials have shown that treatment can improve disability in patients with arthralgia. However, interpreting the clinical relevancy of the improvements in Health Assessment Questionnaire Disability Index (HAQ-DI) is hampered by the lack of a defined minimal clinically important difference (MCID) in this disease stage. Results from other disciplines than rheumatology suggested that the MCID depends on absolute severity values. Therefore, we hypothesised that the MCID for HAQ-DI in RA depends on absolute values. We aimed to investigate this and, if so, to determine the MCID for disability in the risk setting.

Methods: We studied the literature and determined the correlation of baseline HAQ-DI and MCID estimates in RA. To determine the MCID in arthralgia, we studied 97 patients treated with methotrexate in the TREAT EARLIER trial with HAQ-DI data at baseline and 12 months. At 12 months, a short-form 36 questionnaire anchor question compared patients' general health to that of 1 year before. The MCID was determined using the mean change in HAQ-DI score of patients reporting 'somewhat better' and 'somewhat worse'.

Results: In RA, the MCID estimates ranged from -0.06 to -0.38, and higher absolute HAQ values correlated with a higher MCID. In the at-risk patients studied, the MCID for improvement was -0.07±0.28. Likewise, for deterioration, the MCID was +0.05±0.6.

Conclusion: In arthralgia at-risk for RA, the MCID for improvement in HAQ-DI is -0.07. This is lower than generally reported in RA. This implies that in arthralgia, compared with RA, smaller improvements in HAQ-DI are clinically relevant.