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Flashcards in Muscle disease Deck (52):

Define rhadomyolysis

lysis of mm fibres


What is Equine Rhabdomyolysis Syndrome?

mm cramping/ pain that occurs usually during or following exercise


Other names - Equine Rhabdomyolysis Syndrome

- monday morning disease
- set-fast
- azoturia
- myoglobinuria
- tying up


Presentations of Equine Rhabdomyolysis Syndrome

- ACUTE; may require tx, possibly emergency
- BETWEEN EPISODES: in a horse that has had several / multiple episodes (requires investigation of cause)


CS - Equine Rhabdomyolysis Syndrome - during episode

- stiff movements
- pain
- sweating
- tachycardia
- myoglobinuria
- plasma CK and AST
- r/o other dz


What is CK?

Creatine Kinase (NOT creatinine kinase)


Urine appearance -Equine Rhabdomyolysis Syndrome

coke coloured (myoglobinuria) but doesn't have to look like this


How do plasma CK and AST change during a bout of Equine Rhabdomyolysis Syndrome?

See graph


Tx - acute exertional rhabdomyolysis

- analgesics (NSAIDs, opiates)
- IV/oral fluids
- diuretics (to maintain urine output in attempts to prevent/minimise nephrotoxic effects of myoglobin.
- avoid NSAIDs in severe myoglobinuria as both cayse renal damage so risk of acute renal failure


How is myoglobin nephrotoxic?

causes epithelial cells in renal tubules to slough off --> renal tubular cast


Dx - exertional rhabdomyolysis b/w episodes

EXERCISE TEST: do 20 mins lunge exercise, trot and canter, take pre and post 6 hour exercise CK measurement. >100% rise in CK significant, some individuals may be significant if 20% rise, some vets also measure AST


Aetiology - exertional rhabdomyolysis



Outline acquired exertional rhabdomyolysis

* OVEREXERTION: eccentric contraction, metabolic exhaustion, oxidative injury
- electrolyte imbalance
- hormones?
- infxn


Outline inherited exertional rhabdomyolysis

- recurrent exertional rhabdomyolysis d/t defective Ca regulation
- polysaccharide storage myopathy


What to consider in horse that undergoes repeated episodes of tying up

- consider acquired cases and if possible rule ou
- inherited causes more likely (certain acquired causes ay precipitate an attack in a genetically susceptible animal)


2 forms of genetic repeated exertional rhabdomyolysis

- recurrent exertional rhabdomyolysis of TBs
- polysaccharide storage myopathy (PSSM1)


Outline recurrent exertional rhabdomyolysis (RER)

- defect in Ca regulation
- small group of (related) TBs in USA
- unknown is all TBs with RER have same defect
- unknown if similar disorder occurs in other breeds (likely)
- commonest in young nervous fillies
- approximately 5% TBs affected


Prevention - RER

- Oral dantrolene: a Ca release channel blocker, for TBs with presumed Ca homeostasis problem
- High fat/ low carbohydrate problem: rice bran, vegetable oil, commercial
- Regular exercise/ turnout


Outline PSSM1

- affects QH, warmbloods, drafts, cobs, others
- heritable (autosomal dominant)
--> exertional rhabdomyolysis
- occasionally mm atrophy/ weakess in drafts
- high prevalence in some draft breeds (>50%)
- abnormality of glucose metabolsim
= mutation in glycogen synthase gene in skeletal mm
- mostly subclinical


What is glycogen synthase?

enzyme to form 1-4 links b/w glucose monomers to form glycogen


Outline DNA test for PSSM1

- blood (in EDTA) or hair pluck
- some horses with characteristic pathology don't have the mutation - 'PSSM2'


Dx - PSSM1

- DNA test
- mm biopsy (internalised nuceli non-specific but suggestive of myopathy, polysaccharide inclusions detected by PAS stain which stains glycogen pink)


Tx = PSSM1

- high fat, low carbohydrate diet (as RER)
- daily/regular exercise
- if necessary start with just hand walking and increase gradually every day


What is exhausted horse syndrome?

- a type of exertional rhabdomyolysis syndrome
- usually associated with long rides, often in hot, humid conditions, especially relatively unfit animls
- endurance rides/ races
- 3 day eventing/ cross country
- hunting


What happens in an exhausted horse? 3

- glycogen depletion from mm
- electrolyte loss from sweat
- hypovolaemia


CS - exhausted horse

- depression
- dehydration, anorexia, decreased thirst
- increased RR and HR
- pyrexia
- poor sweating response
- poor jugular distension, increased CRT, decreased pulse pressure
- decreased gut sounds
- laminitis
- synchronous diaphragmatic flutter ('thumps')
- mm pain and stiffness


Describe synchronous diaphragmatic flutter/ thumps

- subtle
- abdominal mm contract regularly --> flank twitch (often in time with heart as phrenic nn picks up vibrations from heart mm contractions)
- associated with hypocalcaemia


Tx - exhausted horse

- IV/oral fluids, supplement with electrolytes if necessary
- rapid cooling, misting tents
- check for evidence of rhabdomyolysis (CK and AST)


Prevention - exhausted horse

- training, heat acclimatisation
- free access to water and administer electrolytes during ride
- frequent veterinary checks


Which dogs are affected by rhabdomyolysis?

- exercising Sled dogs and greyhounds (likely slighly different dz as endurance vs. sprint)
- CS: myoglobinuria, elevated CK, hyperthermia, renal failure


Other names - coccygeal mm injury

- limber tail
- cold tail
- rudder tailed


Breeds affected by coccygeal mm injury

working breeds - labs, pointers etc


What is coccygeal mm injury?

- pain at tail base
- mild CK eleveation
- recovery over severeal days
- cold, exercise, swimming,
- prolonged cage transportation


Tx - coccygeal mm injry

- rest


What does Ryanidine Receptor 1 (RYR1) do?

allows Ca to leave SR --> cytoplasm to allow mm contraction


Name 3 channelopathies

- Sarcolemmal sodium pump
- Ryanodine receptor (RYR1)
- Calcium ATPase


What does sarcolemmal sodium pump channelopathy affect??

--> hyperkalaemic periodic paralysis


What does RYR1 channelopathy do?

--> MH in:
- mixed breed dogs
- landrace pigs
- QHs
(mutation causes Ca to stay at high levels in cell --> cell membrane breaks down. Pork --> PSE = pale, soft and exudative)


What does Calcium ATPase channelopathy do?

--> congenital pseudomyotonia in Chianina cattle (mm remain contracted all the time)


What is myostatin?

important paracrine hormne that is inhibitory to mm growth. A TGF-b protein


What do mutations in myostatin cause?

- Belgian Blue and Piedmontese cattle (mutation in both myostatin alleles --> double mm appearance where the mm fibres are huge, not actually 2 of each mm)
- Bully Whippets (heterozygotes for myostatin and run faster so popular in racing)
- Baby superman (son of olympic athlete)
- racehorses (variations in myostatin gene make horses particularly well suited to either sprint or endurance racing, tests for this £1000)


What happens with a mm strain injury?

- overstretching of mm --> fibre disruption --> inflammation and healing with fibrosis
- mild ot severe (complete rupture)
- recovery rapid - low grade injuries
- fibrous tissue may predispose to reinjury or contracture
- Dx: palpation and US


What is fibrotic myopathy in horses?

- common in QH
- semitendinosus usually affected, sometimes semimembranosus or gracilis
--> characteristic gait (affected HL smacks down on floor)
- CAUSES: mm tear, IM injection, neuropathy


Tx - fibrotic myopathy

- rest
- sx resection of fibrous tissue or tenotomy


What is atypical myopathy?

- acute onset severe myopathy in horses at pasture
- fat accumulation in cardiac and skeletal mm
- CK and AST massively increased
- mm biopsy pre or post-mortem (triceps, intercostal, diaphragm)
- v high mortality (cardiac arrhythmias, weak diaphragm)


What is acyl CoA dehydrogenase important for?

fat breakdown


Cause - atypical myopathy?

- associated with ingestion of hypoglycin A (found in seeds of box elder tree - USA, sycamore tree - UK).
- metabolite MCPA is a potent inhibitor of acyl-coA dehydrogenase (fat breakdown)


Tx - atypical myopathy

- all speculative
- riboflavin (vitamin B2 supplementation)
- carnitine supplementation (protein that helps shuttle fat into mitochondria)
- support carbohydrate metabolism (insulin, glucose)


Dx - atypical myopathy

* mm biopsy
- urine/plasma acyl carnitine, organic acids, hypoglycin measurement?


Which animals are affected by muscular dystrophies?

- DOGS - golden retrievers, others
- CATS - sphynx/ Devon Rex
- Humans - DMD


Dx - muscular dystrophies

- usually with IHC


Cause - mm dysrophies

- 65% DMD patient have out-of-frame deletions
- Becker MD have in frame deletions
- n.b. these are both human diseaes