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Muscle disease Flashcards

1
Q

Define rhadomyolysis

A

lysis of mm fibres

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2
Q

What is Equine Rhabdomyolysis Syndrome?

A

mm cramping/ pain that occurs usually during or following exercise

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3
Q

Other names - Equine Rhabdomyolysis Syndrome

A
  • monday morning disease
  • set-fast
  • azoturia
  • myoglobinuria
  • tying up
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4
Q

Presentations of Equine Rhabdomyolysis Syndrome

A
  • ACUTE; may require tx, possibly emergency

- BETWEEN EPISODES: in a horse that has had several / multiple episodes (requires investigation of cause)

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5
Q

CS - Equine Rhabdomyolysis Syndrome - during episode

A
  • stiff movements
  • pain
  • sweating
  • tachycardia
  • myoglobinuria
  • plasma CK and AST
  • r/o other dz
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6
Q

What is CK?

A

Creatine Kinase (NOT creatinine kinase)

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7
Q

Urine appearance -Equine Rhabdomyolysis Syndrome

A

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

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8
Q

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

A

See graph

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9
Q

Tx - acute exertional rhabdomyolysis

A
  • 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
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10
Q

How is myoglobin nephrotoxic?

A

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

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11
Q

Dx - exertional rhabdomyolysis b/w episodes

A

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

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12
Q

Aetiology - exertional rhabdomyolysis

A
  • ACQUIRED

- INHERITED

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13
Q

Outline acquired exertional rhabdomyolysis

A
  • OVEREXERTION: eccentric contraction, metabolic exhaustion, oxidative injury
  • electrolyte imbalance
  • hormones?
  • infxn
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14
Q

Outline inherited exertional rhabdomyolysis

A
  • recurrent exertional rhabdomyolysis d/t defective Ca regulation
  • polysaccharide storage myopathy
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15
Q

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

A
  • consider acquired cases and if possible rule ou

- inherited causes more likely (certain acquired causes ay precipitate an attack in a genetically susceptible animal)

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16
Q

2 forms of genetic repeated exertional rhabdomyolysis

A
  • recurrent exertional rhabdomyolysis of TBs

- polysaccharide storage myopathy (PSSM1)

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17
Q

Outline recurrent exertional rhabdomyolysis (RER)

A
  • 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
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18
Q

Prevention - RER

A
  • 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
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19
Q

Outline PSSM1

A
  • 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
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20
Q

What is glycogen synthase?

A

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

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21
Q

Outline DNA test for PSSM1

A
  • blood (in EDTA) or hair pluck

- some horses with characteristic pathology don’t have the mutation - ‘PSSM2’

22
Q

Dx - PSSM1

A
  • DNA test
  • mm biopsy (internalised nuceli non-specific but suggestive of myopathy, polysaccharide inclusions detected by PAS stain which stains glycogen pink)
23
Q

Tx = PSSM1

A
  • high fat, low carbohydrate diet (as RER)
  • daily/regular exercise
  • if necessary start with just hand walking and increase gradually every day
24
Q

What is exhausted horse syndrome?

A
  • 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
25
What happens in an exhausted horse? 3
- glycogen depletion from mm - electrolyte loss from sweat - hypovolaemia
26
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
27
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
28
Tx - exhausted horse
- IV/oral fluids, supplement with electrolytes if necessary - rapid cooling, misting tents - NSAIDs - check for evidence of rhabdomyolysis (CK and AST)
29
Prevention - exhausted horse
- training, heat acclimatisation - free access to water and administer electrolytes during ride - frequent veterinary checks
30
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
31
Other names - coccygeal mm injury
- limber tail - cold tail - rudder tailed
32
Breeds affected by coccygeal mm injury
working breeds - labs, pointers etc
33
What is coccygeal mm injury?
- pain at tail base - mild CK eleveation - recovery over severeal days - cold, exercise, swimming, - prolonged cage transportation
34
Tx - coccygeal mm injry
- rest | - NSAIDs
35
What does Ryanidine Receptor 1 (RYR1) do?
allows Ca to leave SR --> cytoplasm to allow mm contraction
36
Name 3 channelopathies
- Sarcolemmal sodium pump - Ryanodine receptor (RYR1) - Calcium ATPase
37
What does sarcolemmal sodium pump channelopathy affect??
--> hyperkalaemic periodic paralysis
38
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)
39
What does Calcium ATPase channelopathy do?
--> congenital pseudomyotonia in Chianina cattle (mm remain contracted all the time)
40
What is myostatin?
important paracrine hormne that is inhibitory to mm growth. A TGF-b protein
41
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)
42
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
43
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
44
Tx - fibrotic myopathy
- rest - NSAIDs - sx resection of fibrous tissue or tenotomy
45
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)
46
What is acyl CoA dehydrogenase important for?
fat breakdown
47
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)
48
Tx - atypical myopathy
- all speculative - riboflavin (vitamin B2 supplementation) - carnitine supplementation (protein that helps shuttle fat into mitochondria) - support carbohydrate metabolism (insulin, glucose)
49
Dx - atypical myopathy
* mm biopsy | - urine/plasma acyl carnitine, organic acids, hypoglycin measurement?
50
Which animals are affected by muscular dystrophies?
- DOGS - golden retrievers, others - CATS - sphynx/ Devon Rex - Humans - DMD
51
Dx - muscular dystrophies
- usually with IHC
52
Cause - mm dysrophies
- 65% DMD patient have out-of-frame deletions - Becker MD have in frame deletions - n.b. these are both human diseaes

Neurology (26 decks)

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