Skeletal Muscle Pathology
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What biochemical markers indicate damage to muscle integrity?
- Creatinine kinase (CK)
- Aspartate amiotransferase (AST)
Why is the release of myoglobin bad for animals?
Myoglobin is nephrotoxic so damage to the kidneys can further compromise the animals
How are do you prepare a section of skeletal muscle for histological examination?
Undermine and clamp before incisions, fix, and release once fixed.
What causes the onset and then resolution of rigor mortis?
- Onset - ATP depletion
- Resolution - protein degredation
What factors can affect the colour of skeletal muscle on PM examination?
- Necrosis causes pale muscle
- Age - younger animals tend to have paler muscle
- Species - e.g. pork is a different colour to beef
- Other pathology e.g. anaemia
- Inflammation or haemorrhage causes red muscle
What is the smallest unit of skeletal muscle?
What is the difference between type I and type II skeletal muscle fibres?
- Type I skeletal muscle fibres are slow response, slow fatigue, use oxidative (aerobic metabolism), are postural muscles and 'red' muscle
- Type II skeletal muscles are fast response, fast fatigue, glycolytic (anaerobic) metabolism, propulsive muscles, 'white' muscle
What does skeletal muscle look like on longitudinal and transverse histological section?
- Longitudinal - broad stripes of myofibres that contain fibrils. These are surrounded by basal laminae and CT. Cells are very long, have multiple nuclei distributed along the length of the cell.
- Transverse - endomysium surrounding each fibre stretching out to the perimysium, nuclei are at the edges of the cells
True or false: muscle cells have the ability to enter the cell cycle?
False - muscle cells are permanent cells and have no capacity to enter the cell cycle/divide
Describe what happens to muscle cells after they are injured, depending on whether the basal laminae is intact or destroyed
- Basal laminae intact - macrophages enter and remove debris, satellite cells become myoblasts, myoblasts fuse to form myotubules, essential structures reformed, nuclei move to peripheral position - REGENERATION
- Basal laminae destroyed - if satellite cells survive multinucleate muscle giant cells develop - FIBROSIS
Explain the differences in the following terms that describe injury to skeletal muscle ) focal monophasic b) multifocal monophasic c) focal polyphasic
- a) one site and injury occurred at one time
- b) injury happened at one time but affected many muscles
- c) injury happened at one site but happened many times
What happens to muscles when they undergo atrophy?
The myofibrils contract and collapse, so muscle volume decreases
List the different causes of muscle atrophy
- Cachexia associated with disease
What causes of muscle atrophy are progressive/rapid?
Disuse, starvation/emaciation and cachexia are all slowly progressive. Whereas denervation is rapid atrophy.
What is hypertrophy?
An increase in size of skeletal muscle by adding myofibrils
What are the three types of hypertrophy?
- Physiological - increased work/exercise
- Compensatory - hypertrophy of remaining myofibres in a partially denervated muscle
Give an example of a degenerative, inflammatory, inherited muscle disease
- Degenerative - ischaemia, nutritional, toxic, exertional, traumatic
- Inflammatory - bacterial, parasitic, immune mediated
- Inherited - muscular dystrophy
What type of ischaemic problem is common in cats?
When may ischaemic muscle damage occur in cows?
In downer cows
Muscles are very prone to oxidative injury. What type of deficiency would predispose an animal to this?
Vitamin E or selenium
What disease is often associated with oxidative injury of muscles in livestock?
White muscle disease
What causes atypical myopathy in horses?
The toxin hypoglycin A present in sycamore seeds
What animals are sensitive to ionophore toxicity?
Horses > livestock
What is 'capture myopathy'?
Seen in highly strung wild animals due to extreme exertion and restraint (both physical and metabolic trauma is caused)
Give examples of degenerative traumatic causes of myopathy
Crushing injuries, lacerations, tearing or ruptures
How does bacterial infection get into muscles?
Through penetrating wounds e.g. injections and bites, adjacent infections, haematogenous spread
What bacteria causes 'Blackleg'?
What is 'blackleg'?
A bacterial infection that causes spore formation in skeletal muscle. This leads to lameness, swelling, pain, subcutaneous emphysema and sudden death.
True or false: there is a vaccination available for blackleg?
If you palpate the skin of an animal with blackleg what does it feel like?
It feels live bubble wrap due to all the gas formation
Give an example of a parasitic cause of inflammatory myopathy
- Neospora canium - dogs and cows
- Trichinella spiralis - pigs
- Sarcocytis spp - tapeworm intermediate stage in muscle
What is masticatory muscle myositis?
An immune mediated inflammatory cause of myopathy in dogs
What are the clinical signs of masticatory muscle myositis?
- Acute - symmetrical swelling of muscles of mastication, pain, cannot open mouth
- Chronic - atrophy, cannot open mouth
What type of test is available for masticator muscle myositis?
Type II myosin antibody test
Which breeds are predisposed to muscular dystrophy?
Golden retrievers and CKCSs
What is muscular dystrophy?
A progressive weakness and skeletal muscle atrophy beginning within days of birth in most severe cases
What causes muscular dystrophy?
The absence of cytoskeletal protein dystrophin causing repeated necrosis and regeneration of fibres
True or false: primary muscle neoplasia is rare?
What can cause secondary muscle neoplasia?
Extension from nearby tissues, injection site sarcoma, mast cell tumours, infiltrative lipoma
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