Fig. 4

The histopathological appearance of the pericardium. a A hematoxylin and eosin-stained section of the pericardium showed lymphoplasmacytic inflammation with scattered plasma cells among a fibrous stroma (original magnification, ×200). b The elastica Masson–Goldner-stained section showed marked fibrous thickening of the pericardium extending into the fatty tissue (original magnification, ×40). c and d Formalin-fixed, paraffin-embedded tissue with immunostaining directed against immunoglobulin G (c) and immunoglobulin G4 (d); immunoglobulin G and immunoglobulin G4 staining, original magnifications, ×200. The ratio of immunoglobulin G4-positive plasma cells/immunoglobulin G-positive plasma cells was 42%