Equine Muscle Disorders Flashcards
what is special about muscle physiology in horses?
increased muscle mass
greater locomotor efficiency
high mitochondrial volume
high intramuscular store of glycogen
high buffer and lactate transport capacity
can improve all of the above with training
what gene determines whether they are better at distance or sprint?
myostatin gene
when does sporadic exertional rhabdomyolysis occur?
after very hard exercise
unfit horse
when does recurrent rhabdomyolysis occur?
beginning of light exercise
stress
what is recurrent rhabdomyolysis due to?
abnormal intracellular calcium regulation causing lower threshold for contracture
what are the chief complaints with rhabdomyolysis?
reluctance to move
discolored urine
more in quarter horses and draft horses
what are some distinguishing physical exam findings with rhabdomyolysis?
hard muscles
muscles sensitive to touch
what is the main pathogenic mechanism of rhabdomyolysis?
myocyte lysis
what can you test to check for rhabdomyolysis?
creatine kinase
aspartate transaminase
lactate dehydrogenase
what does creatine kinase do in an injury?
increases by 6 hours and peaks at 12 hours after
if ongoing injury, will continue to rise
when does lactate dehydrogenase increase with muscle injury?
by 2 days
will continue to rise with ongoing injury
what are some key diagnostic test results with rhabdomyolysis?
muscle pain
markedly elevated muscle enzyme activities
myoglobinuria
what are the main treatments for rhabdomyolysis?
rest
intravenous fluid therapy for perfusion and kidneys
manage/monitor electrolytes
flunixin meglumine NSAID if well hydrated
acetominophen if worried about AKI
butorphanol or morphine if severe pain
acepromazine as anxiolytic if euvolemic
what are the clinical signs of polysaccharide myopathy?
severe cases indistinguishable from exertional rhabdomyolysis
chronic low-grade disease: poor performance
what happens in polysaccharide storage myopathy I?
glycogen made all the time but not broken down properly
how can you test for polysaccharide storage myopathy?
take creatine kinase before and 6 hours after trotting
genetic test if PSSM-1
muscle biopsy
what are the main treatments for polysaccharide storage myopathy?
rest
IV fluids if myoglobinuria
low-nonstructural carbohydrate diet
what are the chief complaints with atypical myopathy?
same as exertional rhabdomyolysis but not associated with exercise
more severe
sudden death
what is the pathogenesis of atypical myopathy?
hypoglycin A in sycamore and box elder
multiple acyl CoA deficiency
who gets post-anesthesia myopathy?
large or heavily muscles horses
who can get nutritional myodegeneration (white muscle disease)?
foals
lambs
kids
which muscle is affected by white muscle disease?
more on red (type I oxidative) muscle fibers: use beta oxidation
skeletal and cardiac muscle
how can you treat white muscle disease?
inject vitamin E and selenium
add vitamin E and selenium to diet
poor prognosis if heart involvement
what is the distinguishing physical exam finding with vitamin E deficiency myopathy in an adult?
muscle atrophy
what is the main pathogenic mechanism in hyperkalemic periodic paralysis?
genetic defect in voltage-gated sodium channel
is hyperkalemic periodic paralysis associated with muscle damage?
no
who is hyperkalemic periodic paralysis traced back to?
quarter horse stallion named Impressive
what are the main treatments for hyperkalemic periodic paralysis?
IV dextrose or calcium
acetazolamide
low-potassium diet
which MHC heavy chain is fast twitch?
2X
which MHC heavy chain is slow twitch?
1
when does sporadic exertional rhabdomyolysis occur?
toward end to extreme exercise
several hours after exercise or next day
how common is recurrent rhabdomyolysis?
5% thoroughbred racehorses less than a year
complex heritable component
which muscles should you especially palpate for rhabdomyolysis?
epaxials
gluteals
what is released when myocytes rupture?
myoglobin
other intracellular proteins
electrolytes
why is hypocalcemia seen with rhabdomyolysis?
calcium binds free actin and myosin
where are isoenzymes for creatine kinase?
gut
brain
what is lactate dehydrogenase critical for?
pyruvate-lactate shuttle
why are intravenous fluids given for rhabdomyolysis?
improve perfusion
prevent renal failure
how can rhabdomyolysis be managed?
exercise: consistent daily exercise, slow warm up/cool down
recurrent: short periods exercise- 10 minutes
trace minerals and electrolytes in feed
electrolytes in water to exercising horses
why does cell swelling and lysis occur with polysaccharide myopathy?
cannot use stored glycogen: insufficient ATP for membrane pumps
who usually has polysaccharide storage myopathy type 2?
warmbloods
which polysaccharide storage myopathy has a known genetic cause?
type 1
who usually gets polysaccharide storage myopathy type 1?
quarterhorse types and continental drafts
documented in 20 breeds
what is the dietary management of polysaccharide storage myopathy?
lower glycogen production
avoid high-glycemic feeds
feed low-starch, low-sugar
substitute fats for sugars
supplemental vitamin E
how can you diagnose atypical myopathy?
creatine kinase 100k to millions
severe acidosis
not associated with exercise
how can vitamin E deficiency myopathy be diagnosed in an adult?
usually no elevated creatine kinase
low plasma vitamin E
responds to treatment: vitamin E
which horse breeds are more likely to have hyperkalemic periodic paralysis?
quarteerhorses and crosses
paint horses
appaloosas
lineage tracing back to Impressive
are heterozygotes usually abnormal or normal in hyperkalemic periodic paralysis?
normal
homozygotes abnormal
why doess weakness happen with hyperkalemic periodic paralysis?
myocytes unable to repolarize fast enough
when does hyperkalemia occur with hyperkalemic periodic paralysis?
only during episode
some horses remain normokalemic
how can hyperkalemic periodic paralysis be treated?
regular gentle exercise: epinephrine
oral glucose
intravenous glucose
calcium gluconate
inhaled albuterol or oral clenbuterol
acetazolamide
furosemide if no acetazolamide
low potassium diet
what is acetazolamide?
carbonic anhydrase inhibitor diuretic
potassium-wasting diuretic
