Acquired and genetic myopathies Flashcards
What is the proper name for Azoturia/Tying up?
Equine Rhabdomyolysis Syndrome
What are the signs you might observe during an episode of rhabdomyolysis?
Stiff movements
Pain
Tachcardia
What are the clinpath changes in a horse that has recently had an episode of exertional rhabdomyolysis?
Myoglobinuria
Increased plasma CK and AST
Which stick around longer in the blood.. AST or CK?
AST sticks around much longer
What is the treatment for acute exertional rhabdomyolysis?
NSAIDs or opiates for pain
Fluids and diuretics to minimise nephrotoxic effects of myoglobin
How do you test for exertional rhabdomyolysis between episodes?
Exercise test: 20 mins trot and canter on the lunge, CK levels pre exercise and 6 hrs post
What level of increase in CK is needed in the exercise test for it to be considered significant?
>100%
What are the acquired causes of exertional rhabdiomyolysis?
Overexertion
Electrolyte imbalance
Hormonal influence?
Infectious causes
What are the inherited causes of exertional rhabdomyolysis?
Repeated exertional due to calcium regulation defect, or polysaccharide storage myopathy
What is RER?
Recurrent exertional rhabdomyolysis
Recognised in thoroughbreds
What percentage of TBs are affected with RER and which group are most at risk?
About 5%
Young nervous fillies most likely to be affected
How do you treat RER?
Dantrolene - Calcium release channel blocker
High fat low carb diet
regular exercise/turnout
Which breeds are especially affected by PSSM-1
Cobs, quarter horses, warmbloods, drafts & others
Which gene is mutated in PSSM-1?
Mutation in glycogen synthase gene in skeletal muscle so can’t make glycogen
How do you diagnose PSSM-1?
DNA test available - Submit blood in EDTA or hair pluck
Muscle biopsy-polysaccharide inclusions
How do you treat PSSM?
High fat low carb diet
DAILY exercise
What are the changes in the body in an exhausted horse (e.g. relatively unfit horse after a long day hunting)
Glycogen depletion from the muscles
Electrolyte loss from sweat
Hypovolaemia
What are the clinical signs in the exhausted horse?
Depression
Dehydration, anorexia, decreased thirst,
Increased RR and HR
Poor sweating response
Laminitis
Pyrexia
Poor jugular distenstion, increased CRT, decreased pulse pressure
Synchronous Diaphragmatic flutter (thumps)
Muscle pain and stiffness
What is thumps?
Synchronous diaphragmatic flutter
When the diaphragm twitches in time with the heart beat
How do you treat exhausted horse?
Fluids (oral or IV) with or without electrolytes
Rapid cooling
NSAIDs
Check for evidence of rhabdomyolysis (CK, AST)
Which other species can rhabdomyolysis occur in?
Dogs eg sled dogs
What is coccygeal muscle injury?
Pain at the tail base with mild elevations in CK
What breeds often get coccygeal muscle injury?
Working breeds eg labrador, pointer
What kinds of activities predispose to Coccygeal muscle injury?
Cold exercise, swimming, long cage transportation
How long does it take to recover from coccygeal muscle injury and what is the treatment?
Recovery over several days
Treatment: rest and NSAIDs
What is the name of the condition which causes hyperkalaemic periodic paralysis in quarter horses?
Sarcolemmal sodium pump channelopathy
(can’t swap sodium for potassium)
What is the cause of malignant hyperthermia and which species/breeds does it affect?
ryanodine receptor channelopathy
Landrace pigs
mixed breed dogs
quarter horses
Which breed is affected by calcium ATPase channelopathy?
Chianina cattle
causes congenital pseudomyetonia
What is the cause of ‘double muscle syndrome’ as seen in belgian blues and bully whippets?
Myostatin mutation
How do you get muscle strain injury?
Overstretching of muscles –> disruption of fibres
leads to inflammation and fibrosis
Which breed is fibrotic myopathy common in?
Quarter horse
Which muscleis most often affected by fibrotic myopathy?
Which other 2 muscles are often implicated?
Semitendinosus
Semimembranosus & Gracilis
3 common causes of fibrotic myopathy
IM injection
Muscle tear
Neuropathy
What is the treatment for fibrotic myopathy?
Rest NSAIDs, surgical resection of fibrous tissue or tenotomy
What clinpath findings do you expect to see in a horse with atypical myopathy?
Huge increase in CK and AST
Blood can look red with myoglobin
Due to fat build up in the skeletal and cardiac muscle
Histo slide = fat in muscle
What is the proposed pathogenesis of atypical myopathy?
Eating of plants which have MCPA as a metabolite. Hypoglycin A common precursor.
MCPA inhibits acetyl-CoA dehydrogenase, interferes with b oxidation
What are the suggested treatments for atypical myopathy? NB all speculative
Riboflavin (vitamin B2)
Carnitine supplementation
Support carbohydrate metabolism (glucose, insulin?)
How do you diagnose AM?
Muscle biopsy
urine/plasma acyl carnitine
hypoglycin measurement?
What does this histo section show?
Muscular dystrophy
Why do AM horses die?
Normally cardiac arrhythmias or diaphragm weakness
very high mortality rate about 80%
Duchen MD = **** frame deletions
Out of
Becker MD = ***** deletions
in frame
