Background Impairment of functional capacity is a common problem for patients with rheumatoid arthritis (RA) with high costs for the patient and society in general. Therefore, it is important to explore its determinants.
Objectives To find variables that can explain the functional capacity of patients with RA.
Methods A cross-sectional study was conducted in 82 established RA patients under biological therapy from a university hospital of Portugal. The analyzed variables were: age, sex, age at disease onset, education level, disease duration, time under biological therapy, serology status, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), tender and swollen joint count, DAS28, radiographs scored by the van der Heijde modified Sharp method (sSharp score), HAQ (functional capacity), EQ-5D, physical and mental health summary measure of SF36 (SF36-PSM and SF36-MSM) and pain and patient global assessment of disease activity by visual analog scale (P-VAS and PGA-VAS). Descriptive statistics were calculated for several demographic and clinical characteristics. Pearson or Spearman correlations were used for the assessment of the correlations between the different variables and the HAQ. Subsequently, multiple linear regression analysis (backward selection) was carried out using the HAQ as the dependent variable. As independent variables, were included variables that had a significant association with HAQ in the univariate analysis.
Results Most of patients (87.8%) were women; mean (SD) age was 55 (±11) years. Mean age at diagnosis was 34 (±11) years with a disease duration of 21 (±9) years. Most of the patients (n=72, 86.7%) were positive for rheumatoid factor and/or anti–citrullinated protein antibodies. Mean time under biological therapy was 7 (±3) years. Mean of HAQ was 1.19 (±0.66), DAS28 3.29 (±1.13), total sSharp score 191 (±77), EQ5D median (min,max) was 0.69 (-0.35,1.00), PSM 34.93 (14.21,65.50) and MSM 52.18 (23.07,66.23). HAQ correlation coefficients (r) above 40% were observed with, in descending order, EQ5D, PSM, PGA-VAS, P-VAS, age, total sSharp, hands and total erosion scores; p<0.001 for all analysis. DAS28 score and age at disease onset had a weak correlation (r=0.30 and 0.34, respectively, p<0.05). Time under biological therapy, serology status, disease duration, joint count, ESR and CRP showed weak or no significant correlations. Multiple regression analysis identified age, sex, total sSharp score, EQ5D and PSM as determinants of physical function (r=0.73, r2=0.71; p<0.001). Absence of collinearity among the variables included in the regression model was observed.
Conclusions This study, showed that older age, female gender, quality of life and joint damage are the main determinants of functional capacity. Furthermore, our results suggest that in established disease, HAQ score measures mainly the degree of joint damage and not the disease activity.
Disclosure of Interest None declared