Development of functional impairment and disability in rheumatoid arthritis patients followed for 20 years - relation to disease activity, joint damage and comorbidity.

Objectives. To study the course of impairment measured by signals of functional impairment (SOFI) and disability measured by health assessment questionnaire (HAQ) over 20 years in rheumatoid arthritis (RA) patients followed from diagnosis. To explore the contribution of disease activity, joint damage and comorbidity to variation of SOFI and HAQ over time. Methods. RA patients diagnosed 1985-1989 were prospectively monitored. There were 183 patients, 63 % were women, mean (SD) age was 52 (12) years. Disease activity was measured by 44-joint DAS, joint damage by Larsen score and comorbidity by Charlson Comorbidity Index. Contribution of comorbidity, DAS and joint damage on development of SOFI and HAQ was studied at 0,5,10, 15 and 20 years follow up (hierarchical regression model) and over the total study period using (longitudinal regression model). Results. SOFI progressed over 20 years while progression of HAQ levelled off after 10 years. For SOFI, DAS and joint damage contributed the most (2-28 % and 3-31%, respectively). Over 20 years, SOFI was explained by DAS (20%), joint damage (20%), age (7%) and comorbidity (4%). For HAQ, DAS contributed the most (4-24%). Over 20 years, HAQ was explained by DAS (20%), joint damage (2%), gender (7%), comorbidity (6%) and age (4%). Conclusion. Over 20 years, 51% of the variation of SOFI and 39% of the variation of HAQ could be explained by age, gender and variations in comorbidity, disease activity and joint damage. Over time, disease activity contributed significantly to both SOFI and HAQ. Joint damage contributed predominantly to SOFI. © 2014 American College of Rheumatology.