Muscles Degenerative - Pathology
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Degeneration
- 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
Muscle Calcification
Muscle Ossification
Muscle Pigmentation
Muscle Necrosis
Muscle Atrophy
Toxic Myopathy
Endocrine Myopathy
Nutritional myopathy
White muscle disease
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
Equine Rhabdomyolysis
Porcine Stress Syndrome
Neuromuscular junction diseases
Aquired myasthenia gravis
- See congenital MG
Botulism
Circulatory disturbances
Congestion
- Localised or generalised stasis -> dark red muscle
- E.g. in ruminal tympany (bloat) - congestion of muscles cranial to thoracic inlet
- May resemble haemorhage grossly
Ischaemia
- Firstly segmental necrosis
- -> death of satellite cells
- Causes regeneration but myoblast precursors have to be recruited from viable fibres
- -> death of all cells
- Mostly healed by fibrosis and scar formation
- May attempt regeneration by budding
Main causes:
- Vascular occlusion
- Infarction from embolism is rare due to collateral circulation
- Extension of infarcts depends on size of vessels occluded
- Small capillaries -> segmental necrosis
- Large arteries -> whole muscle areas, including sattelite cells, are killed
- Healed by fibrosis
- May be due to:
- Blockage of iliac arteries by aortic-iliac thrombosis in horses
- Blockage of aortic bifurcation in cats
- Dirofilaria immitis arteritis in dogs
- Vasculitis due to bluetongue virus in sheep
- Equine purpura haemorrhagica
- Non-contagious, sporadic
- Grossly:
- Subcutaneous oedema
- Scattered haemorrhagic foci throughout skin and muscles
- Vasculitis -> infarcts of muscles
- May cause myoglobinuria if extensive
- Possibly immune mediated
- In horses post streptococal infection, especially strangles
- External pressure
- During prolonged recumbency, e.g. anaesthesia, inability to rise, or due to too tightly fitting bandages or casts
- Post anaesthesia myopathy especially in horses
- Dorsal recumbancy -> gluteals and longissimus ischaemia
- Lateral recumbancy -> triceps brachii, pectoralis, deltoideus and brachiocephalicus ischaemia
- Caused by pressure on muscle > perfusion pressure of capillaries
- Downer cows - vetral recumbency -> ischaemia of pectoral muscles and muscles of limbs tucked under the animal
- Pregnant ewes with twins or triplets -> internal abdominal oblique muscle ischaemic necrosis -> potential rupture
- Muscle swelling where it cannot expand
- E.g. supracoracoid muscle infarction in some breeds of turkeys after flapping their wings
- Surrounded by inelastic fascial sheath and bone
- E.g. supracoracoid muscle infarction in some breeds of turkeys after flapping their wings
Trauma
- Due to:
- Direct transection of myofibres
- Compression of myofibres
- Secondary from haemorrhage (bruising)
- 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