Lame - muscle pathology Flashcards
Why does myofibre necrosis due to injury usually only affect a myofibre segment rather than the entire length of the myofibre?
Because myofibres are multinucleate so only the bit associated with the affected nucleus is lost
When does global necrosis of entire length of myofiber occur?
Uncommon
Usually only crush injuries or widespread ischaemia
What is the first part of the process of muscle response to injury?
Fibres swell - hypercontraction
Eosinophilia occurs
Striations are lost
Fragmentation of the myofibre
What is fragmentation of the myofibre in response to muscle injure? What does it look like?
The myofibre breaks up and calcifies - creates chalky white streaks
Why do macrophages infiltrate damaged myofibres?
To clear the cytoplasmic debris
How do damaged myofibres reform into healthy myofibres after damage?
Satellite cells migrate into wounded area and differentiate into myoblasts
Myoblasts fuse into a myotube
Plasmalemma reforms
Nuclei migrate to periphery
Cross striations appear
What is a focal, monophasic degeneration in muscle injury? What is an example?
A single injury - all myofibres injured at the same time
Eg. intramuscular injection
What is a multifocal, monophasic degeneration type of muscle injury? What is an example?
A single insult to the whole muscle
Eg. toxin exposure, single episode of overly strenuous exercise
What is a focal polyphasic degeneration type of muscle injury?
Repeated injury at the same site in a muscle
What is a multifocal polyphasic degeneration type of muscle injury?
Repeated insult to the whole muscle
New lesions form while regeneration takes place
Eg. Repeated exposure to toxin, nutritional deficiency, ongoing degenerative process
What species/type of animals get white muscle disease?
Cattle, horses, sheep, goats
Neonates from selenium deficient mothers
What causes white muscle disease?
Selenium/vitamin E deficiency
How does selenium/vitamin E deficiency cause injury to muscles causing white muscle disease?
Oxidative injury to myofibres - muscle contraction produces lots of free radicals
Loss of antioxidant defence mechanisms causes damage
What muscles are affected with white muscle disease?
Cervical neck muscles for suckling
Proximal limb muscles
Tongue
Masticatory muscles
Myocardial muscles - cardiac failure
What is an example of exertional myopathy in wild animals?
Capture myopathy - wild animals with acute myonecrosis after considerable exertion before capture
What is another word for exertional myopathy?
Rhabdomyolysis
What exertional myopathy/rhabdomyolysis is seen in horses?
Tying up
What type of disorder is equine polysaccharide storage disorder? What causes it?
Autosomal dominant disorder - point mutation (in some cases)
What type of fibres are affected by equine polysaccharide storage disorder?
Type 2 fibres
What muscles are affected by equine polysaccharide storage disorder?
Gluteals
Semimembranosus
Semitendinosus
Epaxial muscles
What is equine atypical myopathy?
Degeneration of postural and resp muscles after eating toxin in maple or sycamore leaves/seeds
What species is immune mediated myositis seen in?
Mostly dogs
What muscles are affected in immune mediated myositis? Why?
Masticatory muscles - contain type 2M myosin which is unique isoform to them
What is seen on histopathology for immune mediated myositis?
Eosinophils
Plasma cells
Lymphocytes
Macrophages
Fibrosis
What are the clinical signs ofr immune mediated myositis?
Acute - jaw muscles swell, pain, cant open jaw
Chronic/insidious - atrophy, decreased jaw mobility
What causes fibrosis of the muscles in immune mediated myositis?
Basal lamina being damaged by immune cells
What causes infectious myositis?
Direct penetration from wounds or injections
Haematogenous spread
Extension of nearby infection
What primary muscle tumours are there? Are they common?
Rhabdomyomas/myosarcomas
Rare
What primary tumours of associated tissues can cause muscle tumours?
Fibrosarcomas
Haemangiosarcoma
Infiltrative lipoma
