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what are two enzymes that elevate with muscle injury? which has shorter half life/rises first?
- CK (quick to rise and 2hr half life; very sensitive for mm damage)
- AST (peaks 12-24 hr after injury; present for 7-10d)
- (LDH not specific)
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what diagnostic test can evaluate muscle tone?
electromyography
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what is purpose of scintigraphy?
diagnosing deep muscle disease that is not palpable
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what are recommended sites for muscle biopsy?
- semimebrinous
- middle gluteal
- biceps femoris
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what is a specific disorder of muscle tone?
hyperkalemic periodic paralysis
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what horses get HYPP?
- quarter, paint, appaloosas
- descendants of QH Impressive
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how does horse with HYPP present?
- myotonia, muscle fasciculations, sweating and weakness
- prolapsed 3rd eyelid
- dyspnea if resp. muscles affected
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what is the physiologic problem that causes HYPP?
point mutation in the Na channel of skeletal muscle - excess influx of Na/efflux of K so too close to threshold - persistent depolarization of muscle
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Can you test a horse for the genetic mutation associated with HYPP?
- yes, DNA test is definitive (phenylalanine to leucine substitution)
- electromyography can reveal evidence of HYPP
- (inducing signs w/oral KCl is not recommended)
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If a horse exibits signs of acute episode of HYPP, what should you do?
- drive potassium back into cells using *Karo syrup or IV dextrose*
- OR elevate threshold potential with *Calcium* (so harder to cause action potential even w/ the present excess K)
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how is HYPP managed long term?
- Acetazolamide = K+ wasting diuretic
- avoid diets high in K = no alfalfa, molasses
- regular exercise and frequent, small meals
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what is a syndrome of muscle cramping that occurs during exercise or physical exertion?
rhabdomyolysis
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what are 4 etiologies of rhabdomyolysis?
- nutritional
- inflammatory (clostridial)
- exertional
- traumatic (post-anesthesia)
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what is common name for nutritional rhabdomyolysis? what is deficient in the diet?
- white muscle disease
- deficient vitE or selenium
- affects skeletal and cardiac muscle; <1 yr old usu.
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what are some findings on MDB in horse with nutritional myodegeneration?
- elevated CK/AST
- myoglobinuria
- (can also run tests that measure selenium/E levels)
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what is purpose of testing GSH-Px levels?
levels will be low because it's a selenium dependent glutathione peroxidase that forms in RBCs
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How many times does CK need to be increased to indicate rhabdomyolysis?
5 fold increase
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what are necropsy findings suggestive of acute white muscle disease? chronic?
- acute: coagulative necrosis, white streaks
- chronic: calcification and IM edema
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what form of rhabdomyolysis is associated with fever and systemic toxemia with high mortality rate?
- inflammatory - clostridial myonecrosis
- aka: black leg, gas gangrene, malignant edema
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how is clostridial myonecrosis treated?
- aggressive penicillin
- fasciotomy (filet open tissues, debride and aerate)
- laminitis prophy
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which horses get recurrent exertional rhabdomyolysis or "tying up"?
- thoroughbreds (autosomal dominant trait)
- 67% females
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what are some predisposing environmental triggers for tying up?
- >2kg of sweet feed per day
- exercise duration/intensity and exercising while lame
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what are clinical signs of RER?
- severe cramping of hindlimb muscles
- sweating, anxiety, tachycardia, tachypnea
- some become recumbent if severe enough
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what will MDB reveal with episode of RER?
- very high CK >100,000; elevated AST
- myoglobinuria
- azotemia (beware of pigment nephropathy)
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what are diagnostic findings on muscle biopsy with RER?
- more centrally located nuclei (should be peripheral)
- but normal glycogen staining
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how is acute RER treated?
- IV fluids to avoid renal damage from myoglobin
- NSAIDs with caution
- sedative/tranquilizers to reduce anxiety and pain
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what is involved in long term management of RER?
- daily exercise
- minimize stress/use Acepromazine as needed
- low carbs/high fat (corn oil/rice bran for more calories)
- give dantrolene (muscle relaxer) as preventive treatment before exercise
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What is monday morning sickness? what horses are affected?
- polysacharide storage myopathy = glycogen storage disorder, store glycogen and polysaccharide in myocytes
- QH, paints, drafts, warmbloods
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if horse has persistently elevated CK/AST, even at rest, what are expected findings with an exercise challenge if he has PSSM?
at least a 3fold increase in CK within 4-6 hours of exercise
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what is needed for definitive diagnose of PSSM? what are expected results?
- biopsy semimem/semitendinous muscle
- abnormal glycogen staining using PAS
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what is a horse with PSSM's ability to synthesize glycogen?
- increased ability and increased sensitivity to insulin
- glycogen branching synthase 1 deficiency
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how is PSSM managed?
- do not confine to stall; plan exercise routine
- decrease CHO, incr. fats
- *diet alone is not enough, must combo with exercise*
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what are the two types of post anesthetic myoneuropathy?
- malignant hyperthermia = systemic
- localized
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what is etiology of post general anesthesia myoneuropathy?
- hypoperfusion/ischemia
- PaO2 <60mmHg
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what is "thumps"?
synchronous diaphragmatic flutter in horses suffering fluid/electrolyte imbalance
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how does metabolic alkalosis lead to synchronous diaphragmatic flutter?
causes hypocalcemia because it promotes binding of Ca to proteins (decr. ionized calcium)
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