Misclassification of disease activity when assessing individual patients with early rheumatoid arthritis using disease activity indices that do not include joints of feet.

Objective: To study whether assessment of rheumatoid arthritis (RA) disease activity in individual patients using the disease activity score in 28 joints (DAS28) or other instruments excluding joints of feet may lead to misclassification of disease activity.

Methods: A cohort of RA patients was classified into three 'regional radiographic damage progression' groups: predominantly progression in feet, similar progression in hands and feet and predominantly progression in hands; both in early (0-2 years) and later (2-5 years) disease. Baseline and mean DAS28, individual DAS28 variables and tender joint counts (TJC) and swollen joint counts (SJC) of the feet were compared between groups.