Influence of seasonal changes on disease activity and distribution of affected joints in rheumatoid arthritis

Abstract

Background: Previous studies suggest that RA activity is sensitive to seasonal changes. This study explored the influence of season on RA activity, particularly the distribution of affected joints, using a nationwide database in Japan.

Methods: We investigated 12,839 patients whose RA activity was recorded in spring (n = 3250), summer (n = 916), fall (n = 1021), and winter (n = 7652). Disease activity score (DAS) 28-CRP, simplified disease activity index (SDAI), and clinical disease activity index (CDAI) were used as indices of disease activity. Disease activity was also assessed according to DAS28-CRP scores (remission, low, moderate, or high). The affected joint distribution was investigated using novel joint indices (x, y, z), where x and y are indices for the upper and lower joints, respectively, and z is the index for large joint predominance.

Results: Mean DAS28-CRP and median SDAI and CDAI scores were highest in spring and lowest in fall. There was a significant difference in the DAS28-CRP for fall versus spring and winter. Fall was associated with a higher remission rate, and spring and winter with high and moderate RA activity, respectively. Significant differences in x, y, SDAI, and CDAI scores were found for spring versus summer, fall, and winter, in addition to fall versus winter (except in y). There was no seasonal difference in the z index.

Conclusions: RA activity in the upper and lower extremities may be highest in spring, followed by winter. Seasonal changes should be considered in patients with RA to better understand their symptoms.

Keywords: Disease activity; Epidemiology; Rheumatoid arthritis; Seasonality.

Fig. 1

Seasonal breakdown of rheumatoid arthritis (RA) disease activity according to DAS28-CRP score in 12,839 patients with RA (a) and in a subgroup of 5255 younger patients (< 65 years) (b) in Ninja2016. The proportions of patients categorized as having remission (DAS28-CRP < 2.3), low disease activity (LDA, 2.3 ≤ DAS28-CRP < 2.7), moderate disease activity (MDA, 2.7 < DAS28-CRP ≤4.1), and high disease activity (HAD, DAS28-CRP ≥4.1) in each season are shown in a stacked bar graph. *p < 0.01, **p < 0.05

Fig. 2

Average values for joint index x (upper joint), y (lower joint), and z (large joint index) plotted by season in NinJa2016. Average x, y, and z values for the four seasons are plotted in a three-dimensional format, where x and y are plotted horizontally and z is plotted vertically. The average ± standard deviation values for x, y, and z in each season are as follows: spring, 0.20 ± 0.31, 0.12 ± 0.26, and 0.39 ± 0.43; summer, 0.16 ± 0.28, 0.08 ± 0.23, and 0.34 ± 0.44; fall, 0.15 ± 0.26, 0.08 ± 0.23, and 0.35 ± 0.44; and winter, 0.18 ± 0.29, 0.11 ± 0.26, and 0.38 ± 0.44. Each bar is connected by dotted arrows in the order of the four seasons for clarity