Which histologic findings are characteristic of polymyositis?

Updated: Jan 05, 2021
  • Author: Mythili Seetharaman, MD; Chief Editor: Herbert S Diamond, MD  more...
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Muscle biopsy shows muscle fibers in varying stages of inflammation, necrosis, and regeneration. Findings include focal endomysial infiltration by mononuclear cells (consisting of mostly CD8+ T lymphocytes and macrophages), capillary obliteration, endothelial cell damage, and increased amounts of connective tissue. Later in the course of polymyositis, muscle-cell degeneration, fibrosis, and regeneration may be observed. (See the images below.)

Polymyositis. Histopathology slide shows endomysia Polymyositis. Histopathology slide shows endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis.
Polymyositis. Close view of muscle biopsy, showing Polymyositis. Close view of muscle biopsy, showing chronic inflammatory infiltrate consisting of T lymphocytes, especially CD8+ T lymphocytes.

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