Fig. 1

Histological evaluation of right atrium specimens by light microscopy. a A large inflammatory cell infiltrate (ICI) in the epicardium of a patient with rheumatoid arthritis (RA) (hematoxylin and eosin stain, original magnification × 100). b A large ICI in the epicardium of a patient with ankylosing spondylitis (hematoxylin and eosin stain, original magnification × 400). c A smaller ICI in the myocardium of a patient with systemic lupus erythematosus (hematoxylin and eosin stain, original magnification × 400). d and e Perivascular ICIs in the epicardium of patients with RA (hematoxylin and eosin stain, original magnification × 400). f A smaller ICI located adjacent to adipose cells in the epicardium of a patient with non-inflammatory rheumatic disease (non-IRD) (hematoxylin and eosin stain, original magnification × 400). g Multifocal, moderately increased collagen in the epicardium of a patient with RA (Lendrum-Martius yellow, scarlet, and blue [MSB] stain, original magnification × 100). h Focally pronounced amounts of collagen in the epicardium of a non-IRD patient (Lendrum-MSB stain, original magnification × 100). i Pronounced amounts of adipose tissue in the epicardium of a non-IRD patient (Lendrum-MSB stain, original magnification × 100). j Normal amounts of collagen in the myocardium of a patient with RA (Lendrum-MSB stain, original magnification × 100). k and l Diffusely pronounced amount of collagen in the myocardium of a patient with polymyalgia rheumatica (k Lendrum-MSB stain, original magnification × 100; l Lendrum-MSB stain, original magnification × 400)