Factors associated with normal physical function in patients with rheumatoid arthritis of different ages

Background To investigate factors associated with normal physical function of middle-aged (55-64), old (65-74) or very old (75-84) patients with rheumatoid arthritis (RA). Methods Data from RA patients in the National Database of Rheumatic Diseases in Japan (NinJa) were extracted from April 2017 to March 2018. Factors associated with impaired physical function (Health Assessment Questionnaire Disability Index [HAQ-DI] >0.5) were analyzed by multivariable logistic regression. Association of glucocorticoids (GCs) and age with impaired physical function were presented as adjusted odds ratio (OR) for the 5 groups relative to middle-aged patients without GCs as the reference group. Results Low disease activity (3.3< simplified disease activity index [SDAI] ≤11) or remission (SDAI ≤3.3) was achieved in 3,466 (31.4%) or 3,021(27.4%) of 11,036 patients aged 55-84, respectively. To reduce the influence of joint destruction on HAQ-DI, we assessed the 3,708 patients in both SDAI ≤11 and Steinbrocker stage I/II. About half of the very old patients were receiving methotrexate, which was the lowest proportion amongst the three age groups. GCs were continued in 32.6% of very old patients, and the proportion was higher than in old and middle-aged patients. On the other hand, 16.2% of the very old patients received biological disease-modifying anti-rheumatic drugs (bDMARDs), and the proportions were similar among the three groups. SDAI was higher in patients with HAQ-DI >0.5 at all ages, and GCs was used more frequently in the old and very old patients with HAQ-DI >0.5, compared to those with HAQ-DI ≤0.5. To minimize the influence of disease activity on HAQ-DI, we selected the 2078 patients in both remission and stage I/II. Multivariable analysis revealed the use of GCs further increased the adjusted OR from 4.01 (95% confidence interval [CI] 2.30-6.99) to 6.81 (95%CI 3.65-12.7) in the very old patients, while the adjusted OR was 2.03 (95%CI 1.17-1.13) in the old patients without GCs, 2.22 (95%CI 1.13-4.36) in the old patients with GCs, and 0.73 (95%CI 0.21-2.56) in the middle-aged patients with GCs. Conclusions The negative impact of GCs was likely to most strongly influence physical function of very old patients than middle-aged or old patients.