Background Polyarthritis caused by rheumatoid arthritis has wide variety in size and number of affected joints. In diagnosis and evaluation, swollen joint count and systemic inflammation markers (e.g. serum C-reacive protein (CRP) and erythrocyte sedimentation rate (ESR)) are considered independently. However, when systemic inflammation markers are supposed to reflect the total inflammation in the whole body, the level of the markers should vary according to the size and the number of the swollen, that is, inflamed joints.
Objectives To investigate the correlation between the size of swollen joints with systemic inflammation markers using a large-scale patient database.
Methods NinJa is the largest database of rheumatoid arthritis in Japan in which more than 10,000 patients are registered. Data registered to the NinJa database in 2012 were used. Sixty-six joints were classified into 3 size categories, namely, the digital joints (distal interphalangeal joints, proximal interphalangeal joints, interphalangeal joints, metacarpophalangeal joints and metatarsophalangeal joints) and acromioclavicular joints as small joints (joint surface area1 <10 cm2), the knees as large joints (joint surface area1 >100 cm2), and the others as medium-sized joints (joint surface area1 between 10 cm2 and 100 cm2). Patients with swollen joints limited to one joint-size category were grouped by swollen joint count and compared with patients with no swollen joint. 8574 cases were analyzed. Patients receiving anti-interleukin-6 or Janus-kinase-inhibiting therapies were excluded.
Results Patients with larger numbers of swollen joints tended to show higher levels of both serum CRP and ESR in each joint-size category (Figure 1). In the medium-sized, or knee joint group, these levels were significantly higher than in the no-swelling group and small joint group with the same swollen joint count. Linear regression analysis revealed increments of CRP (mg/L) (ESR (mm/1hr) [95% confidence interval]) per swollen joint as 4.6 [3.7-5.5] (8.9 [6.5-11]) in the knee, 2.3 [2.0-2.7] (4.9 [4.0-5.9]) in medium-sized joints, and 0.56 [0.35-0.77] (0.89 [0.39-1.38]) in the small joints.
Conclusions The strength of swelling in the joints affecting systemic inflammation markers increased with the involvement of larger and/or more numerous joints.
Am J Med Sci. 1956;232:150-5
Disclosure of Interest None declared