Background Mechanical stress would play an important role on inflammation of rheumatoid arthritis (RA). Some studies reported that the dominant hand joints were more affected than the non-dominant ones, but many of them led to the conclusion by evaluating only the right-handed subjects.^1–3Therefore, it is still inconclusive whether right or dominant hand gets more damaged in RA.

Objectives To clarify the relationship of handedness with clinical and radiological joint involvement in RA.

Methods We enrolled a total of 334 patients from the KURAMA (Kyoto University Rheumatoid Arthritis Management Alliance) cohort.⁴ Clinical and radiological joint involvement were compared between the right and left sides, using the tender joint count (TJC) and swollen joint count (SJC) of the 28 joints evaluated for the Disease Activity Score-28, and erosion and joint space narrowing (JSN) of X-rays scored by the modified Total Sharp Score (mTSS). The right-handed and the left-handed groups were separately evaluated.

Results The right-handed were 96% (n=322) and the left-handed were 4% (n=12). Clinical and radiological involvement of upper extremities tended to be worse in dominant hands than in non-dominant ones. (The mean of the score difference (the right-side score minus the left-side score); mTSS 2.33 (p=0.00030), erosion 1.67 (p=0.0081), JSN 0.66 (p=0.14), SJC 0.32 (p=0.00080) and TJC 0.26 (p=0.00010) in the right-handed. mTSS -2.25 (p=0.14), erosion -2.75 (p=0.23), JSN 0.5 (p=0.15), SJC -0.05 (p=0.95) and TJC -0.03 (p=0.72) in the left-handed). There was a statistical significance in the number of affected joints between the right and left upper extremities in the right-handed group. Although this tendency was also seen in the left-handed group, it was not statistically significant likely due to the smaller sample size.

On the contrary, non-dominant foot showed more damage than dominant foot in the right-handed subjects (The mean of the score difference (the right-side score minus the left-side score); mTSS-1.11 (p=0.57), erosion -0.89 (p=0.37), JSN -0.22 (p=0.63)

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Conclusions Handedness influences the laterality of clinical and radiological joint involvement in RA. Laterality of damage in foot may be different from that in hand. This might be because the right-handed usually pivot with the left foot.⁵

1. Mody, G. M. et al. Handedness and deformities,radiographics changes, and function of the hand in rheumatoid arthritis. Ann Rheum Dis 1989;48, 104–107.

2. Koh, H. J. et al. Radiographic structural damage is worse in the dominant than the non-dominant hand in individuals with early rheumatoid arthritis. PLoS One 2015;10:e0135409.

3. Owsianik, D. J. W. et al. Radiological articular involvement in the dominant hand in rheumatoid arthritis. Ann Rheum Dis 1980, 39, 508–510.

4. Terao, C. et al. Three groups in the 28 joints for rheumatoid arthritis synovitis–analysis using more than 17,000 assessments in the KURAMA database. PLoS One 2013;8:e59341.

5. Hatta, T. et al. Lower-limb asymmetries in early and late middle age. Laterality 2005;10:267–77.

Disclosure of Interest None declared