The composition of cellular infiltrates in anti-HMG-CoA reductase-associated myopathy.

INTRODUCTION: To characterize cellular infiltrates in muscle biopsies from patients with anti-3-hydroxy-3-methyl-gulatryl-CoA reductase (HMGCR)-associated myopathy. METHODS: Biopsies from 18 anti-HMGCR myopathy and 7 control dermatomyositis patients were analyzed. RESULTS: CD4+ and CD8+ T-cells were scattered within the endomysium in 50% of anti-HMGCR biopsies. All anti-HMGCR biopsies included increased endomysial and/or perivascular CD163+ M2 macrophages; CD11c+ M1 macrophages were present in 18.8%. CD123+ plasmacytoid dendritic (PD) cells were observed within the endomysium and perivascular spaces in 62.5% of anti-HMGCR biopsies. Membrane attack complex was deposited on endothelial cells in 50% and on the sarcolemma of nonnecrotic muscle fibers in 85.7% of anti-HMGCR cases. Major histocompatibility complex class I antigen was up-regulated in 87.5% of the anti-HMGCR cases. CONCLUSIONS: In addition to necrosis, scattered CD4+, CD8+, and PD cells are characteristic of anti-HMGCR myopathy. Predominant M2 polarization suggests infiltrating macrophages are more likely to be involved with tissue repair than destruction.