case_images: PMC7493364_01
case_images: Clinical course and histopathologic features. a Time course of serum CK levels. b-g Histopathological findings of biopsy of the biceps muscle. b Gomori trichrome staining showing rimmed vacuoles. c, d Serial sections of immunohistochemistry for CD8 and MHC class I. c Endomysial CD8-positive cells surrounding and invading non-necrotic fibers (arrow). d Diffuse expression of MHC class I antigen in non-necrotic fibers. e Immunohistochemistry for p62 showing p62-positive cytoplasmic inclusions. f, g Serial sections of immunohistochemistry for PD-1 and PD-L1. f Endomysial PD-1-positive cells surrounding and invading non-necrotic fibers (arrows). g PD-L1-positive cells and PD-L1 overexpression in the non-necrotic fibers surrounded by PD-1-positive cells. Bars = 50 mum
case_images: 41927_2020_144_Fig1_HTML.jpg
case_images: PMC7493364_01_41927_2020_144_Fig1_HTML.jpg
case_images: Fig1
case_images: After the first infusion of pembrolizumab, his CK levels increased to 1054 IU/L at day 44 (Fig. 1a). Muscle biopsy at day 59 demonstrated prominent variation in muscle fiber size, rimmed vacuoles (Fig. 1b), endomysial CD8-positive cell infiltration with invasion of non-necrotic fibers (Fig. 1c), overexpression of major histocompatibility complex (MHC) class I antigen in non-necrotic fibers (Fig. 1d), and p62-positive inclusions (Fig. 1e). Abundant endomysial PD-1-positive cell infiltration fiber (Fig. 1f), programmed death ligand-1 (PD-L1) overexpression in the invaded fibers, and PD-L1-positive cells (Fig. 1g) were also observed.