MSK pt 4 Flashcards
What’s the pathogenesis of rigor mortis?
- death
- depleted ATP
- sustained contraction
- autolysis
- muscle breakdown
- release of rigor mortis
In broad terms, what are the 2 clinical signs of muscle disease?
- change in muscle shape
- change in muscle function
What are the two types of muscle shape changes that can be shown with muscle disease?
atrophy
hypertrophy/swelling
what are the 4 types of muscle function changes that can be shown with muscle disease?
weakness
spasm
gait abnormalities
esophageal dysfunction (spp. with skeletal muscle in esophagus)
When you suspect muscle disease and do a gross examination, what do you have to keep in mind?
- look at multiple muscles for changes in size, shape, texture – it is a generalized or local change?
- gross appearance can be unreliable and non-specific – history, histopath, supplemental tests are needed
In terms of muscle clinical pathology, muscle damage may result in what 3 changes?
- increase in creatinine kinase (CK)
- increase in aspartate transaminase (AST)
- myoglobinuria (myoglobin in urine)
In terms of gross lesions of muscles with disease, what are the 4 lesions that we need to be aware of?
- pale muscles
- parasitic muscle cysts
- dark red muscle
- green muscle
what are 3 potential causes of pale muscle?
- necrosis
- mineral
- replacement by fat/collagen
what are 2 examples of parasites that cause parasitic muscle cysts?
- Trichinella spiralis
- Sarcocystis sp.
What are 4 potential causes of dark red muscle?
- hemorrhage
- necrosis
- inflammation
- myoglobin staining
What are 2 potential causes of green muscle?
- putrefaction/autolysis
- eosinophilic inflammation
Define these terms:
1. myopathy
2. myositis
3. myonecrosis
4. cachexia
5. polymyositis
- muscle disease
- muscle inflammation
- muscle necrosis
- generalized muscle atrophy caused by disease or malnutrition
- inflammation of multiple muscles
Describe the pathogenesis of muscle necrosis
- muscle damage
- increase in intracellular Ca2+
- mineralization
what does muscle necrosis look like grossly?
acute: red
chronic: chalky white muscle as mineralization progresses
Describe the pathogenesis of muscle regeneration
- myofiber swelling, degeneration, necrosis
- macrophages clear debris
- satellite cells become activated and divide along intact basal lamina
- regeneration
True or false statements:
1. satellite cells are often affected by factors that cause myonecrosis
2. regeneration requires an intact basal lamina or viable satellite cells
3. if either the basal lamina or satellite cells are damaged, healing occurs by fibrosis
- false. they are not often affected.
- false. regeneration requires both!
- true
what is muscle atrophy?
decreased muscle volume; usually reversible is cause is corrected
what are 3 physiologic causes of muscle atrophy? and what do each look like?
- disuse – asymmetrical and localized
- cachexia – symmetrical and generalized
- senility – symmetrical and generalized
what are 3 endocrine causes of muscle atrophy?
- hypothyroidism (dogs)
- hypercortisolism/Cushings (dogs)
- pituitary dysfunction/tumors (horses)
What is denervation atrophy?
muscle fibres require growth factors from nerves for maintenance – loss of nerve supply leads to rapid atrophy
true or false. congenital atrophy is common.
false. it is rare
Describe the pathogenesis of laryngeal hemiplegia in horses.
- L recurrent laryngeal nerve degeneration (possibly due to long length)
- denervation atrophy of L cricoarytenoideus muscle
- laryngeal paralysis
- can lead to loud breathing (roaring) and aspiration pneumonia
When you work out, what is happening to your muscles?
muscle hypertrophy – increase in myofibre diameter
this is physiologic hypertrophy
what are degenerative muscle diseases?
myofibre necrosis not caused by inflammation
Muscle infarction requires occlusion of ____ blood vessel or severe _______ vascular damage to occur
large
intramuscular
Name 3 potential causes for this lesion
necrosis, mineral, replacement by fat/collagen
Name 2 potential causes for this lesion
Trichinella spiralis
Sarcocystis sp.
Name 4 potential causes for this lesion
necrosis
inflammation
myoglobin staining
hemorrhage
Name 2 potential causes for this lesion
putrefaction/autolysis
eosinophilic inflammation
Myofibres, fibroblasts, and satellite cells have different susceptibilities to hypoxia. List them from most susceptible to least
myofibres
satellite cells
fibroblasts
regenerative ability depends on what?
time in hypoxic state
what does severe, prolonged hypoxia result in? why?
healing by fibrosis
fibroblasts are less susceptible to hypoxia than myofibres or satellite cells
What would an aortic thromboembolism in a cat lead to in terms of muscles?
circulatory degenerative myopathy
cuts off blood flow to both hind legs, leading to hypoxia and infarction
Describe the pathogenesis of compartment syndrome?
- muscle damage
- inflammation and swelling
- increased intramuscular pressure whereby fasica coverage muscle can’t expand
- ischemic necrosis
Recumbency in LA (like in a downer cow or after sx) is caused by what? describe the pathogenesis.
ischemic necrosis of muscles under pressure
- pressure on muscle arterial supply
- compartmental syndrome
- reperfusion injury when pressure relieved
What species are affected by nutritional myopathies? what example did we go over?
neonatal livestock
White muscle disease
What is the cause of white muscle disease?
nutritional deficiencies of selenium (major cause) and vitamin E (minor cause)
Why does a deficiency of selenium cause white muscle disease in neonatal livestock?
selenium is an important antioxidant, and skeletal/cardiac muscles generate high amounts of free radicals – tissues where cell damage from oxidative injury is most severe.
What are the gross lesions of white muscle disease? where are these lesions most obvious?
muscles are pale pink and/or white (degeneration and mineralization)
associated lesions: myocardial degeneration & mineralization; aspiration pneumonia (secondary to impaired swallowing)
most obvious in high workload in neonates (nursing muscles: tongue, cervical muscles, masticatory muscles, proximal limbs)
This is muscle from a calf neonate. What is the lesion?
white muscle disease from hypovitaminosis E
Describe the pathogenesis of ionophore (monensin) toxicity.
- ionophores = growth promoting feed additives
- at toxic levels, they disrupt ion equilibrium
- Ca2+ overload
- skeletal and cardiac muscle necrosis
- death
Which species is affected by ionophore toxicity? And why?
horse
they accidentally feed on cattle rations/feedmill mixing errors
what are the gross lesions of ionophore toxicity?
acute (1-2 days): no lesions
subacte: pale streaks in muscle (necrosis)
survivors: myocardial fibrosis
Horse heart. what is the pathology?
ionophore toxicity –> myocardial necrosis
Toxic plants affect ____ on _____. there are several species of toxic plants. They are more common in _____ climates.
livestock, pasture
southern
Tell my how exertional myopathies occur
over-exertion –> myonecrosis
What important examples of exertional myopathies do we need to know?
- capture myopathy
- exertional rhabdomyolysis
Tell me the pathogenesis of capture myopathy
- capture & restraint of wildlife (and sometimes dom. spp.)
- struggling and stress
- massive myonecrosis
- death
This is the muscle from a deer. What is the pathology?
Capture myopathy that lead to muscle necrosis
What is exertional rhabdomyolysis? what species does it occur in?
skeletal muscle lysis
mainly horses, but rarely affects dogs (athletes like greyhounds and sled dogs)
what are the synonyms of exertional rhabdomyolysis in horses?
“typing up”, Monday morning disease
What are the clinical signs of exertional rhabdomyolysis? What are the predisposing factors?
C/S: stiff gait, swelling, sweating
PF: selenium/vitamin E deficiency, EPSSM
what are the gross lesions of exertional rhabdomyolysis?
red swollen muscles, myoglobinuria
Just know that traumatic myopathies exist and can be caused by lacerations, sx incisions tearing from exercise, etc
this is pretty straightforward. if you cut through muscle, you injure it lol
When does true myositis occur?
when inflammation is the cause of muscle damage, and not the cellular response to injured muscle
describe the pathogenesis of localized bacterial myositis?
- introduction of bacteria (inoculation/wounds)
- suppurative inflammation and necrosis
- abscess formation and extension along fascial planes in severe cases
You have to know 3 species of bacteria that cause localized bacterial myositis. Tell me what they are and what species they affect?
Streptococcus zooepidemicus – horse
Trueperella pyogenes – cattle/sheep
Corynebacterium pseudotuberculosis – sheep/goats
This is the heart muscle of an ox. What is the lesion? What is the etiology (most likely)?
bacterial myositis caused by Trueperella pyogenes
What are the gross lesions of bacterial myositis?
abscesses forming
yellow-green fibrinopurulent material in muscle and along fascial planes
suppurative inflammation
Clostridial myositis is a special case. Tell me about Clostridium spp. and the 4 species names we have to know
ubiquitous spore-forming anaerobic bacteria
C. perfringens, C. chauvoei, C. septicum, C. novyi
What are the gross lesions of clostridial myositis?
localized affected muscles are hemorrhagic, swollen, oedematous, with suppurative inflammation and often gas pockets
what ist he lesion?
clostridial myositis
what is the pathogenesis for clostridial myositis?
- muscle damage creates anaerobic conditions
- spores germinate and bacteria produce toxins
- blood vessel and muscle damage
- hemorrhage and necrosis
- myositis and more anaerobic tissue for bacterial proliferation
Clostridial myositis in cattle (sheep/goats less common) is called what? what clostridium sp. causes it?
blackleg
C. chauvoei
muscle from cow. what lesion?
Clostridial myositis caused by C. chauvoei
what is the pathogenesis of black leg?
- ingested spores cross intestinal mucosa
- hematogenous spread to muscles
- muscle trauma (bruising from handling chutes, crowding, etc)
- localized anaerobic conditions stimulate spore germination
- bacteria proliferate and produce toxins
- vascular damage
- hemorrhage, necrosis, edema
- myositis
How does a cow with black leg usually present? what are the gross lesions of black leg?
acute death
skeletal muscle hemorrhage, edema, crepitus, myonecrosis
What is clostridial myositis in horses called? What Clostridium sp. is it caused by?
malignant edema, gas gangrene
C. septicum (most often)
What is the pathogenesis of equine clostridial myositis?
- usually secondary to penetrating wound that creates localized muscle damage and introduces spores
- germinate in anaerobic conditions
- bacteria proliferate and produce toxins
- vascular damage
- hemorrhage, necrosis, edema
- myositis
This is the muscle from a horse. It had a wound that was healed 4 weeks ago, and you felt crepitus near the old wound. What is the lesion?
Clostridial myositis caused by C. septicum
Pyogranulomatous and fibrosing glossitis:
1. what is it?
2. affects who?
3. what is the inciting cause?
4. clinical signs?
5. associated with what microorganisms?
- inflammation of the tongue skeletal muscles (actinobacillosis)
- cattle
- oral wounds/plant debris
- dysphagia, excessive salivation
- Actinobacillus lignieresii (wooden tongue, main pathogen), A. bovis (lumpy jaw)
This cow tongue. what is the lesion? what are 2 possible etiologies?
pyogranulomatous and fibrosing glossitis
Actinobacillus lignieresii or A. bovis
tongue from cow. ignore arrow. What is the pathology?
pyogranulomatous and fibrosing glossitis
what are the gross lesions of pyogranulomatous and fibrosing glossitis?
multifocal areas of pyogranulomatous inflammation surrounded by fibrous connective tissue
locally-extensive area of necrotizing and pyogranulomatous glossitis
this on the tongue of cows
Viral myositis:
1. rare or common?
2. T or F: they often don’t have primary lesions in other systems.
- rare
- false. they often DO have common lesions in other systems
Bluetongue virus in sheep causes systemic vasculitis, which can cause muscle infarcts. What type of muscle disease is this?
viral myositis
Parasitic myositis:
1. T or F: often there is little or no associated disease.
2. muscle infection occurs in which type of hosts?
- True
- intermediate
We need to know 4 examples of parasites that cause parasitic myositis. What are they and what are their associated mammal species?
Trichinella - pigs
Neosporum caninum (myositis in calves and dogs)
Cysticercus (larval cestode) - cattle,, sheep, goats pigs
Sarcocystis - LA, wildlife
What is immune-mediated myositis? what species does this primarily happen in?
self-reactive T cells attack myofibres, causing myonecrosis
dogs
immune-mediated myositis can happen in horses. Please tell me how (describe pathogenesis)
- post-Streptococcus equi infection
- antibody complexes deposited in blood vessels
- immune-mediated vasculitis
- muscle hemorrhage and infarction
Immune-mediated myositis and Clostridial myositis are similar (they can be differentials for each other). how do you tell them apart?
immune-mediated myositis won’t have gas and there are multiple muscles affected
What is congenital muscular hyperplasia? who does it affect? what is the other name for it?
genetic defect in myostatin gene causing increase in # of myofibres
affects cattle (Belgian blues) and dogs
“double muscling”
This boi is JACKED. what is the lay term for this pathology, and the “real” name (like scientific name lol).
congenital muscular hyperplasia AKA double muscling
Metabolic myopathies:
1. what are they?
2. clinical signs?
- inherited disorders of energy production
- exercise intolerance, cramps, rhabdomyolysis
Glycogen storage diseases are what type of muscle pathology? describe the pathogenesis. who does it affect?
metabolic myopathies
affects cattle, horses, sheep, dogs, cats
defects in glycolysis pathway –> accumulation of glycogen in muscles
What happens when there is a disease of the neuromuscular junction? is it associated with denervation atrophy?
any disorder that disrupts the NMJ, there is severe muscle dysfunction.
it is NOT associated with denervation atrophy
Describe the pathogenesis of botulism.
- infected by Clostridium botulinum
- permanently blocks release of Ash from nerve synapse
- severe flaccid paralysis
- respiratory muscle paralysis
- death
Tell me how botulism causes aspiration pneumonia
dysphagia and tongue weakness from the flaccid paralysis that comes from the block of Ash from nerve synapse, causes aspiration pneumonia
botulism recovery requires what?
new axon sprouting
what is the pathogen that causes botulism?
Clostridium botulinum
Tell me how animals can get botulism. what species is most affected?
ingestion of pre-formed toxin (like in rodent carcasses, in feed, etc) – most common
GI colonization (foals)
deep wound infection (rare)
horses most affected
What are the two forms of Myasthenia Gravis? which is more common?
Acquired (common) and congenital (rare)
what is myasthenia gravis?
immune-mediated disease with autoantibodies against acetylcholine receptors
tell me the pathogenesis of myasthenia gravis. This disease is often associated with what other disease? What is one common sequelae?
- antibodies bind Ach receptors
- block Ash
- muscles can’t contract
- weakness and collapse
often associated with thymus disease (ex. thymoma)
sequelae = aspiration pneumonia
Tick paralysis:
1. what species of tick are responsible?
2. pathogenesis?
3. who is affected?
4. ddx?
5. recovery?
- Dermacentor and Ixodes
- ticks release toxin –> blocks Ash release –> reversible flaccid paralysis
- dogs
- botulism, but dogs are quite resistant
- rapid recovery if tick is removed
What are the two primary muscle neoplasms? are they common or rare?
Rhabdomyoma (benign) and Rhabdomyosarcoma (malignant)
rare
what is the most common location of rhabdomyosarcomas?
urinary bladder
Muscle neoplasia can also arise from other _____ ____ in muscle. _______ is the most common.
support cells, hemangiosarcoma
True or false: muscle is a common site of metastasis with the exception of horses with melanoma.
False. muscle is NOT a common site of metastasis
the exception is horses, where it’s common with melanoma
Equine Polysaccharide Storage Myopathy:
1. which breeds are affected?
2. what is it?
3. how is diagnosis reached?
- warmbloods and drafts mainly - others are also affected
- abnormal glycogen accumulation in muscles likely causes decreased energy in myofibres
- muscle biopsy
Equine polysaccharide storage myopathy:
1. horses with this pathology are prone to what?
2. what are the gross lesions?
- exertion rhabdomyolysis and hindlimb pain
- pale muscles (esp. hind limbs), dark red kidneys from myoglobin, myoglobinuria
Hypokalemic myopathy:
1. which species is affected?
2. what is the pathogenesis?
3. associated with what?
- cattle
- anorexia –> low potassium –> myonecrosis
- history of postpartum ketosis, glucocorticoid treatment, atrial fibrillation, weakness and recumbency (lesions related to recumbency), low serum potassium and high CK/AST
Tell me the pathogenesis of how hypocalcemia causes muscle damage in cattle. What is the lay term for this pathology?
milk fever!
- abnormal postpartum calcium homeostasis
- hypocalcemia
- weakness and recumbency
- muscle damage from recumbency
tell me what prolonged recumbency does to muscles.
ischemic necrosis of muscles from decreased perfusion, compartmental syndrome and reperfusion injury
Porcine Stress Syndrome
1. AKA?
2. what is it?
- malignant hyperthermia
- genetic condition of pigs, related to genetic selection for increased muscle and low fat
Porcine Stress syndrome:
1. pathogenesis?
2. clinical signs?
- abnormal ryanodine receptor (Ca2+ channel) –> excessive muscle contraction
- clinically normal until exposure to halothane anesthesia or high stress. then muscle rigidity and high body temp, progression to death
pigs with porcine stress syndrome have what gross lesions?
muscles are pale pink, swollen, appear cooked, moist
this is pig muscle. the one on the right is normal. what is the pathology of the one on the left?
porcine stress syndrome
Neosporum caninum:
1. what is it?
2. who does it affect and when?
3. clinical signs?
- protozoal parasite
- dogs in utero
- progressive neuromuscular dysfunction in young puppies
neosporum caninum: how does in cause muscle pathology?
infects peripheral nervous system + skeletal muscles. it targets spinal roots, which causes denervation atrophy of hind limb muscles
multifocal myositis - pale, firm, atrophied muscles
this is the muscle of a very young puppy. what is the ethology of the pathology?
Neosporum caninum
What is muscular dystrophy?
inherited, progressive condition with myofibre degeneration and necrosis with regeneration
X-linked muscular dystrophy:
1. which species & breeds are affected?
2. what is it?
3. tell me what sex of animals are affected?
- dogs – many breeds, like Irish Setters, Goldens, Labs (also cats!)
- X-linked recessive disorder that causes a defective dystrophin gene (codes for a muscle membrane protein)
- carrier females produce ~50% affected males
X-linked muscular dystrophy:
1. tell me about the severity
2. the heart has muscles, so it is also affected. tell me how.
3. signs of illness?
- variable. death in neonates to survival >6 months of age
- cardiac fibrosis
- progressive weakness and muscle atrophy due to muscle necrosis with regeneration
what do you think this dog has?
X-linked muscular dystrophy
what are the gross lesions involved with X-linked muscular dystrophy?
diffuse muscle atrophy with splaying of forelimbs
Tell me how hypothyroidism affects muscles.
thyroid hormone is needed for muscle metabolism
low T4 = skeletal muscle weakness and atrophy
peripheral neuropathy contributes to atrophy
what are the clinical signs of hypothyroidism that related to muscles?
generalized weakness, muscle atrophy, laryngeal paralysis, megaesophagus
hypothyroidism may have a similar presentation to another disease. what is the disease and how can you tell the different?
Hypercortisolism
there is muscle weakness/atrophy, but with this disease, there is also symmetrical alopecia
what is masticatory myositis?
immune-mediated inflammation against type 2 myofibres of masticatory muscles (temporalis and masseter)
tell me the gross lesions for acute and chronic masticatory myositis?
acute: bilateral swelling, pain, inability to open mouth
chronic: bilaterally symmetrical atrophy of temporalis and masseter muscles, limited jaw mobility, often severe fibrosis
Masticatory myositis needs to be differentiated from what other muscle pathology? how do you get a definitive diagnosis for masticatory myositis?
immune-mediated polymyositis
definitive dx: serology for anti-myosin antibodies
what is immune-mediated polymyositis?
immune-mediated inflammation that targets myofibres causing necrosis in multiple muscles
which muscles are affected by immune-mediated polymyositis?
all muscles!
temporalis/masseter mm may atrophy and look similar to masticatory myositis
esophageal muscles – dysfunction and megaesophagus
what 3 kitty specific muscle diseases do we have to know?
- x-linked muscular dystrophy (similar to dogs)
- myopathies associated with electrolyte abnormalities (similar to cattle) [hyperthyroidism/chronic renal disease –> hypokalemia –> muscle weakness]
- immune-mediated myositis associated with feline immunodeficiency virus (FIV)
