Background/Purpose:   Rheumatoid arthritis (RA) functional impairment is composed of reversible and irreversible components. The aim of this analysis was to assess the reversible and irreversible components of RA physical function as measured by the Health Assessment Questionnaire (HAQ) in Canadian routine clinical practice.

Methods:   BioTRAC is an ongoing, prospective registry of patients initiating treatment with IFX or GLM for RA, ankylosing spondylitis, or psoriatic arthritis. Eligible participants for this analysis included RA patients treated with IFX enrolled since 2002 or with GLM enrolled since 2010, who had a HAQ >0 at baseline and at least one follow-up assessment with known HAQ score at remission or achievement of low disease activity (LDA). Remission was defined as SDAI ≤3.3, CDAI≤2.8, DAS28 <2.6, or achievement of the following four criteria: SJC ≤1, TJC ≤3, CRP level ≤0.8 mg/dL and MdGA ≤15mm. Low disease activity was defined as SDAI ≤11.0, CDAI ≤10.0 or DAS28 ≤3.2. HAQ scores at the time of RA remission or achievement of LDA represented the irreversible component of the disease functional limitation, namely the residual HAQ score, while the difference in HAQ scores from baseline to remission or LDA corresponded to the reversible component. In addition, the reversibility of HAQ score was determined as the relative improvement in baseline HAQ score at the time of remission or achievement of LDA and, the fraction of HAQ irreversibility was calculated as the residual HAQ score divided by the maximum possible HAQ score. Descriptive statistics were produced for HAQ reversible and irreversible parameters.  The correlation of disease duration with the HAQ irreversible component was described with the Pearson’s correlation coefficient. Multivariate linear regressions adjusted for age, gender, anti-TNF, baseline disease duration and HAQ score at baseline were performed to assess the impact of the type of coverage (private and public) on reversible and irreversible components of the disease. Level of statistical significance was set to 0.05.

Results:   There were 753 patients included in this analysis (499 patients were on IFX and 254 on GLM) with a mean (SD) age of 56.4 (13.4) years, disease duration since diagnosis of 8.7 (9.3) years and HAQ score of 1.5 (0.7) at treatment initiation. The majority of patients were females (74.8%). At treatment initiation, 356 (47.8%) and 289 (38.8%) patients were on public and private drug coverage, respectively. The HAQ reversible and irreversible components in RA are presented in Table 1. Variation in the reversibility of HAQ score was observed among RA patients depending on the target outcome used for the calculation, with 44.8% reversibility reported based on DAS28 remission to 57.6% with SDAI remission and, from 33.1% based on CDAI-LDA to 36.4% with SDAI-LDA. Weak correlations between disease duration and HAQ irreversible component were observed for all the target outcomes with Pearson’s coefficients varying from 0.105 based on derived definition of remission to 0.270 with CDAI remission and, from 0.119 based on SDAI-LDA to 0.202 with DAS28-LDA. Upon adjustment for age, gender, anti-TNF agent, baseline disease duration, and HAQ score at baseline, patients on private insurance were found to have significantly greater HAQ reversibility when assessed with SDAI remission (β= -27.39; P=0.029) and derived definition of remission (β= -17.94; P=0.036) than patients on public coverage. Coverage type was not found to have an impact the fraction of HAQ irreversibility and the irreversible component. Table 1:HAQ Reversible and Irreversible Components in Rheumatoid Arthritis.  

Conclusion:   The results of this Canadian longitudinal observational study show variability in the proportions of reversibility and suggest that patients on private insurance at treatment initiation have a greater reversibility of RA functional impairment than patients on provincial coverage. However, the type of coverage did not have an impact on irreversible components of the disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-haq-reversible-and-irreversible-components-measuring-function-in-rheumatoid-arthritis/