To examine predictors of progression of disability in rheumatoid arthritis (RA), as measured by the Health Assessment Questionnaire disability index (HAQ), and to determine rates of progression during biologic treatment.
We followed 18,485 RA patients for up to 11 years (mean 3.7 years) in a longitudinal study of RA outcomes. Patients were characterized as having moderate or severe RA versus less severe RA at study entry. Annualized progression rates were determined in multivariable analyses using generalized estimating equations.
Although all of the demographic and severity characteristics were associated with baseline differences in HAQ score, progression was only associated with age, comorbidity, initial severity, and treatment. HAQ score increased fastest in patients ages >65 years (0.031; 95% confidence interval [95% CI] 0.028, 0.034). HAQ progression was independently associated with the presence of baseline cardiovascular disease, hypertension, diabetes mellitus, and the number of comorbid conditions. Annualized progression rates were greater in patients with mild to inactive RA (0.021; 95% CI 0.019, 0.023) than in moderate to severe RA (0.003; 95% CI 0.001, 0.006). The overall progression rate during biologic treatment was 0.008 (95% CI 0.005, 0.011); for patients with moderate to severe RA, the rate was 0.001 (95% CI -0.005, 0.003).
Age and comorbidity are important predictors of the rate of loss of functional status, and have a stronger effect on HAQ progression than does biologic treatment. There is little difference in progression rates among biologics. Patients with more severe RA progress less than those with less severe RA, a possible function of regression to the mean.