Muscles Developmental - Pathology
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Congenital diaphragmatic defects
- Clefts may lead to herniation of abdominal organs into thoracic cavity in any species
Myofibrillar hypoplasia
- In piglets
- = Splayleg
- May spontaneously resolve
- Unknown cause
- Responsible for significant deaths
Hyperplasia of muscle fibres
- In calves and lambs
- “Double muscling”
- Increased number of myofibres in affected muscle (thighs, rump, loin)
- Predisposes to dystocia
Muscular dystrophies
- Inherited group of degenerative muscular diseases
- Progressive muscle weakness and wasting
- Usually due to a genetic fault -> muscular protein deficiency
- Duchenne MD in humans due to dystrophin deficiency also present in some animals
- Dystrophin gene mutations reported in the Golden Retriever, Rottweiler, German shorthaired pointer and Irish terrier etc.
- Inadequate regeneration, compensatory hypertrophy
- More about Muscular dystrophy
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
- Autoimmune disease
- 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
Canine dermatomyositis
- Hereditary in Collies and Shetland sheepdgs
- Lesions resemble canine polymyositis
- Also degeneration of blood vessels -> muscle microinfarcts
- Usually generalised but temporalis and other masticatory muscles may be involved the most
- Microscopically: inclusion bodies in endothelial cells
- Best place for biopsy is anterior and most superficial temporalis muscle
- Also involves skin, may involve the oesophagus