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What is equine rhabdomyolysis ?

Muscle cramping or pain that occours usually during or following excercise


What are the 2 forms of equine rhabdomyolysis?

Acute (may require emergency Tx)
Between episodes in a horse with recurrent episodic attacks. Requires investigation of the cause


Clinical signs of exertional rhabdomyolysis

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


What does CK Stand for?

Creatine kinase (NOT creatinine)


How long after an acute exertional rhabdomyolysis episode do plasma levels of indicative hormones rise?

CK peaks at 6hrs, halved by 24hrs
AST peaks at 24hrs, takes longer to decrease
- if seeing a horse after the acute attack, have to r/o liver disease as AST will be the only thing raised


Tx acute rhabdomyolysis

-Analgesics (opioids, probably avoid NSAIDs d/t risk of renal failure with myoglobinuria and NSAIDs combo
-IV and oral fluids
- diuretics (prevent or minimise nephrotoxic effects of myoglobin)


How can horses be investigated in between episodes?

Excercise test - 20 mins lunge excercise trot and canter
- pre and 6 hour post excercise CK measurements
- 100% rise regarded as significant but nothing magic about this number!


Acquired aetiology of exertional rhabdomyolysis

Over exertion
- eccentric contraction worse (downhill or jumping work)
- metabolic exhaustion
- oxidative injury
Eletrolyte imbalance
Hormone? Females affected worse than males
Infectious causes


What is DOMS

Delayed onset muscle spasm?


Inherited aetiology of exertional rhabdomyolysis

Recurrent exertional d/t defective calcium regulation
Polysaccharide storage myopathy


Which causes are more likely?

R/o acquired, but inherited more likely


what is RER ?

Recurrent exertional rhabdomyolysis
- defect in calcium regulation that has been studied in detail in small group of related TB
- other TBs affected the same defect?
- similar disorder in other breeds?


Which horses is RER most common in?

Young nervous fillies
5% TBs affected!!


How can RER be prevented?

Oral dantrolene - calcium channel release blocker
- for TBs with presumed calcium homeostasis problem
High fat low carb diet
- rice bran, vegetable oil, commercial
Regular excercise and turnout


What is PSSM1?

Polysaccharide storage myopathy
- 1 = the form with genetic mutation of glycogen synthase in skeletal muscle
- affects QH, warmbloods and draft horses, cobs and many others
- heritable autosomal dominant
- causes exertional rhabdomyolysis
- occasional muscle atrophy/weakness in draft breeds
- abnormal glucose metabolism


Which breed is most commonly affected by PSSM1?

Belgian draft horses >50% carry dominant gene
- not necessarily clinically affected but would be microscopically affected


Alternative names for equine rhabdomyolysis syndrome?

Monday morning disease, set fast, azoturia, myoglobinuria, tying up


What is the action of glycogen synthase?

forms 1-4 links between glucose monomores -> glycogen


How can PSSM be detected? Is it always detectable?

>diagnosis by muscle biopsy
- internalised nuclei = non-specific sign of muscle damage
- polysacharide inclusions diagnositic
> DNA test also available
- submit blood (EDTA) or hair pluck
- if no mutation detected but clinical sings present = PSSM 2


What are polysaccharide inclusions and how are they detected?

- muscle biopsy
- amylase added to break down polysaccharide
- should get rid of all pink staining material with PAS
- in PSSM some pink amylase resistance polysaccharide remains in the muscle cells


Tx and management of PSSM1?@

- ^ fat, v carbohydrate diet
- advise regular daily exercise
- if necessary start with hand walking then increase gradually


What is exhausted horse syndrome?

- long rides, hot humid conditions, esp in unfit animals
- endurance riding
- 3d event
- cross country/hunting
> glycogen depletion from muscles
> electrolyte loss from sweat
> hypovolaemia


Clinical signs of exhausted horse syndrome?

- depression
- dehrydration, anorexia, v thrirst
- ^ RR ^ HR
- pyrexia
- poor sweating
- poor jugular distencsion, ^ CRT, v pulse pressure
- v gut sounds
- lamnititis
- muscle pain and stiffness
- synchronous diaphragmatic flutter (esp. with hypocalcaemia)


WHat is synchronous diaphragmatic flutter?

= Thumps
- electrolyte imbalance esp. hypocalcaemia
- phrenic nerve picks up depolarisation of the heart
- rhythmical contraction in time with the heart


Is rhabdomyolysis seen in dogs?

Yes, esp sled dogs and greyhounds (probably different aetiology between the two)


What signs are seen in dogs with rhabdomyolysis

- myoglobinuria
- elevated CK
- hyperthermia
- renal failure


Tx. exhausted horse syndrome?

- IV/oral fluids + electrolytes
- rapid cooling
- check for evidence rhabdomyolysis (CK and AST)


Prevention exhausted horse syndrome?

- trainaing, heat acclimitisation
- free access to water
- administer eletrolytes during the ride
- frequent vet checks


What is swimmer/limber/cold/rudder tail?

- coccygeal muscle injury
- working breeds labs pointers etc.
- esp if swim a lot
- recovery over several days
- cold, exercise, swimming and prolonged cage transport predispose


Tx rudder tail

rest, NSAIDs


Look at physiology of muscle contraction

- T tubules
- Na channels
- Sarcoplasmic reticulum
- Ryanodine
- Reuptake of Calcium


Give 3 examples of channelopathies

1. Sarcolemmal sodium pump
- Hyperkalaemic periodic paralysis in Quarter HOrses (HYPP)
- autosomal dominant
- all descending from "Impressive" QH sire, very impressive muscling, but had mutation in gene -> leaky Na influx and constant K+ outflow to compensate
- hyperkamaeia -> cardiac arrhythmias
2. Ryanodine Receptor (RYR1)
- malignant hyperthermia in mixed breed dogs, Landrace pigs [PSE meat], QH
3. Calcium ATPase [returns Ca to SR]
- dysfunction -> permenant contraction
- Brodie's disease in humans


Give an eg. of a cell signalling defect

> myostatin
> TGFb protein , paracrine hormone that limits muscle growth
- mutations in Belgian Blue and Piedmontese cattle
-Bully whippets (heterozygotes run faster)
- Baby superman
- racehorses (depending on gene variation makes them better sprinters or endurance horses)


What is muscle strain? How can muscle strain injuries progress to more severe disease?

> muscle strain: overstretching of muscle -> disruption of fibres
- inflammation, healing with fibrosis
- milkd - severe (complete rupture)
- recovery rapid with low grade injuries
- fibrous tissue may predispose to re-injury or contracture
- palpation oand ultrasound to diagnose
> fibrotic myopathy in horses
- esp QH
- usually semitendinosius, sometimes semimembranosus or gracilis
- causes: Muscle tear, IM injection, neuropathy
- characteristic gait (slapping, short stride of affected limb) - do not confuse with Stringhalt


Tx fibrotic neuropathy?

- rest
- surgical resection fibrous tissue or tenotomy


What is atypical myopathy?

Acute onset, severe myopathy in horses at pasture
-- CK and AST massively increased
- muscle biopsy pre/post mortem (triceps/intercostals/diaphargam)
- accumulation of lipid in cardiac/skeletal muscle
- NOT exccercise induced


Clinical signs of atypical myopathy?

- myoglobinuria
- cardiac arrhythmia
- diaphragmatic failure
- death


Aetiology of atypical myopathy?

> Hypoglycin A
- sycamore tree
- unripe Ackee fruit (Jamaican national fruit)
- Box elder in US
- Acer species
> Acyl co-a dehydrogenases inhibited by 'MCPA' metabolite
- important for breakdown of fat and uptake into the mitochondria


Speciulative tx of atypical myopathy

- riboflavin (Vit B2 supplement)
- carnitine supplementation
- support carbohydrate metabolism (?insulin/glucose CRI)


Diagnosis of atypical myopathy?

- muscle biopsy or urine/plasma acyl carnitine, organic acids, hypoglycin measurement
- commercial test likely to become available


Muscular dystrophies

Not gone into yet.. .