Muscle Pigmentation

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  • Lipofuscin
    • Wear and tear pigment accumulating in secondary lisosomes -> converted into compact residual bodies
    • Due to old age, past or recent cachexia or starvation
    • Mostly stored in skeletal muscle of old high producing dairy cattle
    • Masseters and diaphragm mainly involved
    • No clinical importance
    • Histologically:
      • Rounded yellow to brown granules at both poles of nucleus of the skeletal myofiber
  • Melanin
    • As part of congenital melanosis of calves in fascial sheaths and epimysium
    • Grossly - black foci
  • Myoglobin
    • After extensive muscle necrosis - rhabdomyolysis
    • Leaks to adjacent tissue after sudden injury
  • May also be present after some types of intramuscular injections e.g. iron dextran or tetracycline