Muscles Developmental - Pathology

=Muscle Fibre Hyperplasia

Glycogen storage diseases

• Caused by a deficiency of an enzyme
• See general pathology
• Type II glycogenosis
  • Deficiency of acid maltase
  • In Shorthorn cattle
  • Muscular weakness and incoordination
  • Glycogen stored in skeletal muscle, heart and CNS
  • Type I and II muscle fibres contain glycogen vacuoles
• Type III glycogenosis
  • Deficiency of debranching enzyme
  • In dogs
  • Causes hypertrophic cardiomyopathy and hepatomegaly
  • Glycogen in skeletal and cardiac muscle, neurons nad hepatocytes

Steatosis

• Also called lipomatosis
• In cattle, sheep and pigs
• Fat replaces lost muscle fibres
• Pale muscle, bilaterally symmetrical
• No clinical significance
• Noticed at slaughter or necropsy

Myasthenia gravis (MG)

• Acquired
  • Autoimmune disease
    • Antibodies directed against acetyl choline receptors
  • Associated with thymomas, megaoesophagus and dysphagia
  • In adult dogs
• Congenital
  • Inherited deficiency in acetyl choline receptors
  • Rare
  • Newfoundland, Jack Russel Terrier, Springer Spaniels – genetic predisposition
  • In dogs – 4 DLA genes recognized: DLA-12, DLA-88, DLA-79 and DLA-64
  • Associated with HLA gene in humans
  • No antibodies against acetyl choline receptors in serum
  • Non-specific muscle disuse atrophy and fibrosis or no changes on histology
• Both forms manifest as weakness which worsens on exercise