Muscles Degenerative - Pathology

Degeneration

Degenerate muscle fibres (Image sourced from Bristol Biomed Image Archive with permission)

• Different types of degeneration
• May, or may not, be reversible
• Cloudy swelling, hydropic, vacuolar, granular and fatty change
• Occur following many different types of insult and are usually segmental
• If regeneration does not occur after formation of small vacuoles, necrosis follows
  • Vacuolation -> floccular degeneration -> granular degeneration -> hyaline and Zenker’s degeneration
• Vacuolar degeneration:
  • Due to swelling of organelles or due to glycogen or fat accumulation
  • May be caused by hypokalaemia, hyperkalaemia or necrosis
• Histologically:
  • Swollen
  • Hypereosinophilic
  • Lost cross striations

Nutritional myopathy

Exertional myopathies

• Caused by intensive and exhaustive activity of major muscle masses
• Glycogen used up -> local heat and lactic acid -> muscle degeneration
• Other forms include capture myopathy, racing greyhounds, sheep chased by dogs

Neuromuscular junction diseases

Aquired myasthenia gravis

• See congenital MG

Circulatory disturbances

Trauma

• Due to:
  • Direct transection of myofibres
  • Compression of myofibres
  • Secondary from haemorrhage (bruising)
    • May increase muscle pressure -> ischaemia -> necrosis
  • Partial rupture - e.g. of diaphragm in road traffic accident
  • Complete rupture - e.g. quadriceps of racing greyhounds
  • Myorrhexis (tearing) - e.g. slippery floor causing 'splits' in cattle -> adductor muscle tear
• Healing is by regeneration
• Fibrosis (scarring) will compromise function
• During fractures, fragments may cause further trauma if moved