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Abstract
Background The Health Assessment Questionnaire (HAQ) is the most widely used measure of function in studies of inflammatory polyarthritis (IP) and its subset rheumatoid arthritis (RA). Previous research has suggested the mean HAQ over time is j-shaped with an initial improvement followed by an insidious decline. Few studies have attempted to identify distinct subgroups with common HAQ trajectories in IP and RA samples, or considered their validity across cohorts.
Objectives To identify common trajectories of HAQ progression in two large prospective observational studies.
Methods Data of two large inception cohorts, the Early Rheumatoid Arthritis Study (ERAS) and the Norfolk Arthritis Register (NOAR), were used. ERAS recruited patients with RA from 9 hospital clinics in England between 1986 and 1997: N=1460, mean age 55yrs, 66% female, mean symptom duration 8mths. NOAR is a primary care based inception cohort of early IP in Norwich, England. Patients recruited between 1990 and 1994 were included: N=1027, mean age 53yrs, 66% female, mean symptom duration 9mths. In both cohorts, disease activity and HAQ-scores are measured at baseline and at subsequent follow-up visits. To determine trajectories of HAQ progression over time, latent class growth models (LCGM) were applied to the datasets separately. Age, sex, baseline DAS, symptom duration, rheumatoid factor, and fulfillment of ACR criteria were included as predictors of class membership.
Results In both cohorts a 4 class LCGM was selected as providing the best fit. The classes identified were similar in terms of the shape of the trajectories and distribution of patients between classes (see figure). Three classes exhibited a j-shaped trajectory. A fourth class experienced persistently high HAQ that increased early in the course of the disease. In both cohorts older age, female sex, longer symptom duration, fulfillment of ACR criteria and higher DAS were associated with increased likelihood of membership of classes with worse HAQ progression.
Conclusions Four subgroups with common HAQ trajectories were derived from the ERAS and NOAR cohorts. That the subgroups identified were nearly identical supports their validity. Identifying distinct groups of patients at risk of poor functional outcome may help to target therapy to those most likely to benefit.
Disclosure of Interest None Declared