Equine Rhabdomyolysis

• Azoturia (Monday morning disease)
  • Acute
  • Due to exercise following a prolonged period of rest
  • Clincal signs:
    • Unable to move
    • Sweating
    • Tremors
    • Swollen and hard lumbar, gluteal and femoral muscles
  • Myoglobin leaks from muscle cells -> leaks into urine -> urine is dark red/brown (myoglobinuria) -> damages renal tubules
  • Grossly:
    • Salmon pink muscles -> dark, moist, swollen +/- pale streaks
  • Histologically:
    • Segmental myofibre necrosis
      • Multifocal and monophasic, but may be multiphasic if repeated bouts
    • Both, type IIA and IIB fibres affected; type IIB preferentially affected in acute disease
    • Minor inflammatory reaction and calcification

• Tying-up
  • Similar to azoturia but much milder
  • Grossly - normal muscle
  • Histologically - same as azoturia