Muscle Ischaemia

  • Firstly segmental necrosis
  • -> death of satellite cells
    • Causes regeneration but myoblast precursors have to be recruited from viable fibres
  • -> death of all cells
  • Mostly healed by fibrosis and scar formation
  • May attempt regeneration by budding

Main causes:

  • Vascular occlusion
    • Infarction from embolism is rare due to collateral circulation
    • Extension of infarcts depends on size of vessels occluded
      • Small capillaries -> segmental necrosis
      • Large arteries -> whole muscle areas, including sattelite cells, are killed
    • Healed by fibrosis
    • May be due to:
      • Blockage of iliac arteries by aortic-iliac thrombosis in horses
      • Blockage of aortic bifurcation in cats
      • Dirofilaria immitis arteritis in dogs
      • Vasculitis due to bluetongue virus in sheep
      • Equine purpura haemorrhagica
        • Non-contagious, sporadic
        • Grossly:
          • Subcutaneous oedema
          • Scattered haemorrhagic foci throughout skin and muscles
          • Vasculitis -> infarcts of muscles
        • May cause myoglobinuria if extensive
        • Possibly immune mediated
        • In horses post streptococal infection, especially strangles
  • External pressure
    • During prolonged recumbency, e.g. anaesthesia, inability to rise, or due to too tightly fitting bandages or casts
    • Post anaesthesia myopathy especially in horses
      • Dorsal recumbancy -> gluteals and longissimus ischaemia
      • Lateral recumbancy -> triceps brachii, pectoralis, deltoideus and brachiocephalicus ischaemia
    • Caused by pressure on muscle > perfusion pressure of capillaries
    • Downer cows - vetral recumbency -> ischaemia of pectoral muscles and muscles of limbs tucked under the animal
    • Pregnant ewes with twins or triplets -> internal abdominal oblique muscle ischaemic necrosis -> potential rupture
  • Muscle swelling where it cannot expand
    • E.g. supracoracoid muscle infarction in some breeds of turkeys after flapping their wings
      • Surrounded by inelastic fascial sheath and bone