Interrelationship of outcome measures and process variables in early rheumatoid arthritis. A comparison of radiologic damage, physical disability, joint counts, and acute phase reactants.

OBJECTIVE: To investigate the relationship between different outcome and process measures in early rheumatoid arthritis (RA).
METHODS: A 3-year prospective study of 149 patients with early RA (symptoms < 1 year at entry). Results of serial measurements of process variables were transformed into time integrated values for comparison with the outcome measures.
RESULTS: A highly significant correlation was found between the acute phase response, swollen joints, and radiological progression whereas none of these measures correlated with joint tenderness. Physical disability as estimated by the Health Assessment Questionnaire (HAQ) however, appeared to be determined by joint tenderness rather than by joint swelling.
CONCLUSION: In early RA, joint swelling and acute phase reactants appear to be the most appropriate process variables for the prediction of radiological outcome, whereas joint tenderness is a strong determinant of physical disability (HAQ).