Lecture 31: MSK 4 Flashcards
Compare the 3 muscle types
cardaic: striated and involuntary
smooth: non-striated and involuntary
skeletal: striated and voluntary
What is another name for muscle cell
myofibre
What are the features of a muscle cell
multinucleated with a peripheral nuclei
terminally differentialted = no cell division
different types have different contractile properties
depend on innervating neurons
What cells do myofibres come from
myoblasts aka satellite cells
What is a myofibril
collection of myofilaments
What is a myofilament
collection of myofibres
What is a motor unit
spinal nerve and all the muscle fibres it connects to
causes simultaneous contraction of the all the muscle cells in the unit
What are the 3 types of reactions muscle has to injury
gross appearance:
- change in mass/shape/colour
growth change
muscle necrosis
What is a physiologic cause for pallor in muscle
young
What is a cause for green in muscle (non pathogenic)
putrifaction
What is a non pathogenic cause for black in muscle
melanosis of fascia
What is a non pathogenic cause for dark red muscle
hypostatic congestion artifact
hemorrhage
rhabdomyolysis
What changes might you see grossly in muscle that is a response to injury
change in mass
shape change
colour change
mineralization
parasites (cysts)
What are 3 types of growth cahgnes that can occur in response to muscle injury
atrophy: reduce muscle mass duue to reduced size/diameter of muscle fibre
hypertrophy: reversible increase in size/siameter of muscle fibres
hyperplasia: increased number of muscle fibres
What are 4 causes for muscle atrophy
disuse: reduce type 2 fibre
dennervation/neurogenic: rapid atrophy of type 1 or 2 fibres
- if chronic it also has steatitis and fibrosis
malnutrition/cachexia: reduce type 2 fibres
endocrine dz: reduce type 2 fibres
- cushing/hypothyroid
What are the 2 classifications of muscle necrosis
segmental aka zenker degeneration
- muscle cell partially dies but not fully because it is multinucleated
global: complete death of muscle cell
What are the histologic changes that accompany muscle necrosis
myofibril swelling
loss of striation
vacuolation and fragmentation of cytoplasm
mineralization (due to lot of Ca in sarcoplasmic reticulum)
What are 4 requirements for muscle regeneration
satellite cells
intact basal lamina
blood supply
removal of necrotic debris
List the 3 steps of muscle regeneration
macrophage infiltration to remove the debris
- require a blood supply
satellite cells activate and proliferate
now myoblasts fuse and form regenerating myotubules
List the 4 types of muscle injury
focal monophasic
focal polyphasic
multifocal monophasic
multifocal polyphasic
monophasic = 1 incident
- all muscle at same stage of injured
polypahsic: repeat injury
- multiple different stages of muscle regeneration or degeneration
List 5 types of congenital myopathy
congenital muscular hyperplasia
muscular dystrophy
myotonic spastic syndrome
metabolic myopathy
malignant hyperthermia
What is congenital muscular hyperplasia and what causes it?
aka double muscling
due to a myostating gene mutation
causes increase in number of muscle fibres (normal size)
What animals are commonly affected by congenital muscular hyperplasia
belgian blue
whippet
What is muscular dystrophy and what causes it
ongoing necrosis and regeneration
inherited x linked condition
- mutation of dystrophin gene
What animal is primarily affected by muscular dystrophy and what is a common clinical presentation
dogs
plantigrade stance
What is myotonic and spastic syndrome and what causes it
temporary inability of muscle contraction
due to a plasma membrane defect in the Cl channels
What are 2 examples of species specific conditions of myotonic and spastic syndrome
fainting goats
hyperkalemic period paralysis
What animals does hyperkalemic period paralysis affect and what does it present as? What causes it?
quarter horses
transient paralysis/hypotonia
due to a autosomal dominant mutation in the Na channel
What are 2 conditions that cause metabolic myopathy
glycogen storage dsiease
equie polysaccharide storage myopathy
What is glycogen storage disease? Why does it occur?
abnormal skeletal muscle energy metabolism resulting in excessive carb/lipid storage
due to inadequate energy production from (potentially) a mitochondrial defect
What are the clinical signs of glycogen storage disease causing metabolic myopathy
weakness
exercise induced cramps
rhabdomyolysis
What animals are affected by equine polysaccharide storage myopathy
drafts
warmblood
arabian
quarter
What is equine polysaccharide storage myopathy?
It is a carbohydrate disorder causing intracellular glycogen accumulation
What is malignant hyperthermia and what causes it
Caused by ryanodine receptor defect resulting in increased intracellular Ca
- causes prolonged muscle contraction leading to hyperthermia
What are the gross signs of malignant hyperthermia? What animals are primarily affected?
pigs and dogs
pale/soft/exudative muscle (PSE pork)
fast onset of rigor mortis
can cause acute heart failure
What is a main cause of nutritional myopathy? How does the disease differ between cows, pigs, and horses?
vit E and selenium deficiency
cow: white muscle
pig: mulberry heart disease and hepatosis dietetica
horse: yellow fat dz
What are the gross lesions associated with white muscle disease
pale muscle +/- mineralization
brushstroke lesions on the endo and epicardium - preferentially in the LV (vs RV)
- concurrent acute heart failure
skeletal and cardiac lesions are not always together
What are 2 toxin types that can cause a myopathy
ionophores
myotoxins
What animals are affected by ionophores? What are the gross lesions?
horses (contamination of feed with ruminant or poultry feed)
acute muscle necrosis = hemorrhagic or pale
+/- skeletal muscle and myoglobinuria
What is a myotoxin affecting pigs
gossypol (cotton seed)
What is are 2 myotoxins affecting horses
seasonal pasture myopathy
box elder tree
What is senna
a myotoxin
from coffee bean senna
What type of muscle injury do myotoxins cause
multifocal and polyphasic
What are 2 types of exertional myopathy
exertional rhabdomyolysis
capture myopathy
What are the clinical signs of exertional rhabdomyolysis
rhabdomyolysis = skeletal muscle necrosis
myoglobinuria (red wine urine)
What causes exertional rhabdomyolysis? What animals does it affect? What are some alternate names for this condition?
horses and dogs
exercise stress
black disease/monday morning disease/tying up/azoturia
What animals does capture myopathy affect? What is the cause
wildlife
due to stress
causing acute death
What are 2 conditions that cause a circulatory myopathy
compartment syndrome
downers syndrome
What is compartment syndrome? What causes it?
increased intramuscular pressure in non expandable compartment
increased vascular skeletal muscle along with occlusion of large blood vessels or severe intramuscular vascular injury
How does compartment syndrome affect muscle cells? What animal is this common in? How is it commonly treated?
ischemia
- varied susceptibility
most susceptible: muscle fibre > satellite cell > fibroblasts
deep pectoral myopathy in chickens
tx: early fasciotomy to reduce pressure
What is downer syndrome? What animals does it affect most?
increased intramuscular pressure due to body weight pressure
cow and horse
What are the sequelae of downer syndrome
Ischemic necrosis
reperfusion injury
What are 3 types of neuromuscular dysfunction causing myopathy
myesthenia gravis
botulism
tetanus
Compare myopathy due to neuromusclar injury and dennervation atrophy
neuromuscular injury
- failure of signal transmission
- innervation intact
dennervation atrophy
- lack of innervation of tissueW
What causes botulism
clostridium botulinum
What causes tetanus
clostridium tetani
Compare the clinical consequence of botulism and tetanus
botulism
- flaccid paralysis (prevention of presynaptic Ach)
tetanus
- spastic paralysis (prevention of inhibitory neurons)
What are 3 main causes of myositis
suppurative myositis
clostridial myositis
parasitic myositis
What is the route of infection causing suppurative myositis? What is a primary gross lesion
blood borne or direct innoculation
causes intramuscular abscesses
What are 2 common animals that get suppurative myositis? What is the typical causative agents?
horses: in pectoralis
- Cornybacterium pseudotuberculosis
- strep equi
cow: truperella pyogenes
What are the features of clostridia bacteria
gram -
spore forming (environmentally stable)
commensal (except C. chauvei)
many species
List 2 diseases caused by clostridial myositis? What is the causative agent?
malignant edema: C. septicum
black leg: C. chauvei
Compare the clinical signs of malignant edema and black leg
malignant edema: swelling and edema in muscle
black leg: dark red bubbles in muscle with crepitus and rancid butter smell
sporulated and encysts in muscle causing muscle necrosis
anaerobic environments (due to muscle necrosis) allow growth
List 3 common causes of parasitic myositis and the causative agent of each
trichenollosis: larval nematode (zoonotic)
cysticercosis: taniae tapeworm (zoonotic)
sarcocystis: protozoa (incidental)
List 2 causes of non infectious causes of myositis? What type of diseases are they?
auto immune
masticatory muscle myositis
polymyositis
What is masticatory muscle myositis? What animal does it affect?
dogs - GSD
chewing muscle (massetor) inflammation
- unique to canine mastecatory muscles
What is polymyositis? What animal does it mainly affect?
dogs - GSD
generalized myositis
Contrast masticatory muscle myositis and polymyositis
masticatory muscle myositis:
- caused by auto antibody against 2M myosin which is unique to canine mastecatory muscle
polymyositis
- no 2M myostin anti-antibody
What are the main types of primary muscle neoplasia
rare
usually from satellite cells
rhabdomyoma
rhabdomyosarcoma
List 2 types of secondary muscle neoplasias
uncommon
melanoma
infiltrative lipomas
