What factors influence functional ability in patients with rheumatoid arthritis. Do they alter over time?

To describe the changes in functional ability (FA) taking place over 5 yr in patients with rheumatoid arthritis (RA) starting disease-modifying anti-rheumatic drug (DMARD) therapy, to investigate the factors having most influence upon FA and to compare these factors at baseline and after 5 yr of treatment.

Three hundred and sixty-six patients with active RA were studied as part of a 5-yr randomized controlled study of DMARD therapy. FA was assessed by Health Assessment Questionnaire (HAQ) score every 6 months. Multiple linear regression was used to identify factors affecting FA at baseline and at 5 yr. The independent variables used were age, sex, visual analogue scale (VAS) pain, Ritchie articular index, C-reactive protein (CRP), Larsen score and log-transformed morning stiffness (EMS).

Mean HAQ score was 1.64 at baseline, improved by 21% at 1 yr and gradually returned towards baseline levels by 5 yr. At baseline only 34% of variance in HAQ score could be explained; the most significant explanatory variables were the Ritchie articular index and CRP. At 5 yr the variance explained was 60%. The Ritchie articular index remained the strongest factor followed by VAS pain, log(10) EMS and Larsen score.

Improvement in function did occur after commencement of the first DMARD therapy but was not maintained to 5 yr. The most consistent factor affecting function was joint tenderness. Global pain and duration of EMS were of lesser importance. Disease activity measures such as the CRP exerted an influence in the earlier, more active stages of disease: radiographic damage assumed greater importance as the arthritis progressed.