muscle necrosis, myositis Flashcards
What are the 3 gross features of muscle necrosis?
- Pallor of muscle (paleness)
- Swelling (due to edema)
- White streaks (due to concurrent mineralization)
What are the 3 microscopic features of muscle necrosis?
- Fragmented sarcoplasm
- Hyper-eosinophilia
- Regeneration and fibrosis
Recall:
- When muscle cells attempts to regenerate, the nuclei of the myocyte move to the center of the cell.
- Fibrosis = the replacement of normal structural elements of the tissue with excessive accumulation of scar tissue comprised of distorted collagens; occurs after wound does not heal properly.
Where can lesions of muscle necrosis be found in an animal with white muscle disease?
bilaterally symmetrical, polyphasic lesions in the skeletal muscle of the tongue, diaphragm or heart
How do toxic myopathies caused by ionophores lead to muscle necrosis?
Calcium overload in myocytes
This growth-promoting antimicrobial is put in ruminant feed –> horses given this feed –> ionophore infiltrates MØ of muscle fibers 1&2 –> calcium overload in myocytes –> muscle necrosis
How can PSSM pre-dispose horses to exertional rhabdomyolysis?
The PSSM-horse cannot properly metabolize muscle glycogen into glucose, leaving their muscles more prone to injury due to muscle weakness, cramping and tremors (“tying-up”). Events of physical exertion (thus skeletal muscle contraction) in horses with PSSM can lead to the dissolution of skeletal muscle.
Which muscles are most severely affected in muscle necrosis caused by exertional rhabdomyolysis?
the gluteal and lumbar muscles (largest/most powerful)
What is capture myopathy?
An exertional cause of muscle necrosis that arises in response to stress or struggle when wild, non-domesticated species are captured, restrained, immobilized or transported. This leads to acute muscle necrosis signs such as weakness, muscle rigidity and tremors, and acute death.
Explain the two types of ischemic necrosis?
Traumatic causes of muscle necrosis
- Compartment syndrome: exercise –> fascial sheath enclosing the muscle prevents it from swelling –> increased IM pressure –> pressure-induced occlusion of blood flow to that muscle
- Downer syndrome: pressure-induced necrosis in recumbent animals (e.g., ill animals; animals under prolonged anesthesia)
What is myositis?
Non-suppurative inflammation of skeletal muscle caused by an infectious or non-infectious (immune-mediated) agent.
What is the pathogenesis of Blackleg, caused by “Clostridium chauvoei”?
This bacterium is an anaerobic organism. When there is a traumatic muscle injury event and localized hypoxia follows, the bacterial organism’s latent clostridial spores are reactivated and germinate in the muscle.
What lesions indicate myositis caused by “Clostridium chauvoei”? What animals are most susceptible and what parts of the body are commonly affected?
Hemorrhage, emphysema and necrosis.
- emphysema arises from the rapid multiplying of the bacteria, producing gas
Young, rapidly growing ruminants; pelvic and pectoral girdles
What is polymyositis, and what are clinical signs of it?
Immune-mediated, generalized skeletal muscle disorder characterized by acute or slowly progressive generalized muscular weakness and muscular atrophy. E.g., megaesophagus, respiratory distress.
What is masticatory myositis, and what causes it? What are clinical signs?
Immune-mediated inflammation of all muscles of mastication (masseter and temporalis mm.)
Caused by antibodies targeting 2M myosin protein, a distinctive muscle fiber of masticatory muscles.
Characterized by decreased jaw mobility, difficulty eating, and masticatory muscle swelling (acute) or atrophy (chronic).
What are the 4 different types of muscle tumors that are a primary cause of myositis?
Striated muscle: rhabdomyoma and rhabdomyosarcoma
Smooth muscle: leiomyoma and leiomyosarcoma
What are the commonly affected sites for rhabdomyoma?
Heart (pigs & lambs)
Larynx (adult dogs)
Describe the lesion of the intestinal tract and what caused it.
Tan, nodular, well-demarcated mass caused by leiomyoma (benign)
Describe the lesion in the lung and what caused it.
Well-demarcated to coalescing, tan nodules in the lung lobe caused by leiomyosarcoma
Describe the lesion and what caused it.
Red, multi-focal to coalescing lesion on the urinary bladder caused by botryoid rhabdomyosarcoma
“botryoid” = grape cluster appearance
