Toxic Myopathy

• Plants
  • E.g. Cassia occidentalis (coffee senna), Karwinskia humboldtiana (coyotillo), Eupatorium rugosum (white snakeroot), cotton seed
  • Lesion an skeletal and cardiac muscle
  • Grossly:
    • Pale areas with ill-defined borders
    • May involve very extensive necrosis
  • Histologically:
    • Segmental necrosis, no calcification
    • Regeneration may occur in surviving animals
• Drugs
  • E.g. corticosteroids, cholinesterase inhibitors, vincristine, dimethyl sulfoxide (DMSO)
  • Monensin is a coccidiostat toxic to horses, donkeys, zebras, cattle, sheep, dogs and birds
    • Causes muscle necrosis in heart and skeletal muscle
    • Grossly:
      • Pale streaks, mostly in hind limbs
    • Histologically:
      • Segmental necrosis
      • Possibly regeneration in surviving animals
    • Can cause rapid onset recumbency and potentially death
    • Usually due to mixing errors in feed
  • Also from intramuscular injections, e.g. oxytetracycline, lidocaine, chloramphenicol, produce local necrosis
    • As satellite cells are destroyes, repair is via fibrosis with some budding
• Chemicals
  • Iron injections can cause local myonecrosis
• Mycotoxins
  • Metabolites cause persistent tremors
  • Lesions in skeletal muscle only, possibly secondary to sustained contractions (similar to exertional myopathy)
  • Histologically:
    • Tiny foci of segmental necrosis