Muscle Pigmentation

• 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