Acquired and genetic myopathies of horses

Question 0

What are some other names for equine rhabdomyolysis syndrome?

Answer 0

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

Question 1

What is equine rhabdomyolysis syndrome?

Answer 1

Muscle cramping/pain that occurs during or following exercise

Question 2

What are the differential diagnoses for equine rhabdomyolysis syndrome?

Answer 2

Lameness, aortic thrombosis associated with migration of strongyloides worms, colic due to pain in abdominal muscles, laminits, pleuritis and tetanus

Question 3

How does equine rhabdomyolysis syndrome present?

Answer 3

Acutely

Between episodes if a horse has several which requires further investigation

Question 4

How do you diagnose equine rhabdomyolysis syndrome?

Answer 4

Clinical signs of stiff movements, pain, sweating, tachycardia and myoglobinuria
Elevated CK (short half life) and AST (remains higher for longer but liver)

Question 5

What is the treatment for equine rhabdomyolysis syndrome?

Answer 5

Analgesics - NSAIDs or opiates
IV or oral fluids to maintain urine output and minimise nephrotoxicity
Diuretics to maintain urine output and minimise nephrotoxicity

Question 6

How is diagnosis between episodes achieved?

Answer 6

Exercise test of 20 minutes trot and canter with pre and 6 hours post exercise CK measurement with a 100% rise considered significant but can be as low as 50% rise in CK

Question 7

What are the different aetiologies behind acquired equine rhabdomyolysis syndrome?

Answer 7

Overexertion
Electrolyte imbalance (little supporting evidence)
Hormonal influence (females more than males)
Viruses have been implicated

Question 8

What are the different inherited aetiologies of equine rhabdomyolysis syndrome?

Answer 8

Recurrent exertional rhabdomyolysis in Thoroughbreds due to a defect in calcium regulation prevented by oral dantrolene, high fat/low carb diet and regular exercise/turnout
PSSM-1 affecting quarter horses, warmbloods and draft horses leading to abnormal glucose metabolism so excess glycogen in muscle

Question 9

What is the prognosis for equine rhabdomyolysis?

Answer 9

Good provided the horses are managed well

Question 10

What is the exhausted horse syndrome?

Answer 10

Associated with long rides often in hot humid conditions and particularly in relatively unfit animals

Question 11

What causes exhausted horse syndrome?

Answer 11

Glycogen depletion from muscles, electrolyte loss from sweat and hypoolaemia

Question 12

What are the clinical signs of the exhausted horse syndrome?

Answer 12

Depression, dehydration, anorexia, decreased thirst, increased HR and RR, pyrexia, poor seating response propagating pyrexia, poor jugular distension, increased CRT, decreased pulse pressure, deceased gut sounds due to poor blood flow, laminitis, synchronous diaphragmatic flutter, muscle pain and stiffness

Question 13

What is the treatment for the exhausted horse syndrome?

Answer 13

IV or oral fluids with additional electrolytes if necessary, rapid cooling, NSAIDs and check for rhabdomyolysis

Question 14

How can you prevent the exhausted horse syndrome?

Answer 14

Training, heat acclimatisation, free access to water and administration of electrolytes during the ride, frequent veterinary checks

Question 15

Which dog breeds have shown rhabdomyolysis during some activites?

Answer 15

Sled dogs whilst exercising

Greyhounds have myoglobinuria, elevated CK, hyperthermia and renal failure

Question 16

What is coccygeal muscle injury in dogs? What is it also known as?

Answer 16

Pain at the tail base, mild elevation in CK

Limber tail, cold tail, rudder tail

Question 17

What causes coccygeal muscle injury in dogs?

Answer 17

Cold, exercise, swimming and prolonged caged transportation

Question 18

What is the treatment and prognosis for coccygeal muscle injury in dogs?

Answer 18

Rest and NSAIDs

Recovery happens over several days

Question 19

What causes muscle strain injury in dogs?

Answer 19

Overstretching of muscle causes disruption to fibres causing inflammation and healing with fibrosis

Question 20

What is recovery of muscle strain injury like in dogs?

Answer 20

Rapid with low grade injuries but fibrous tissue can predispose to re-injury or contracture

Question 21

What breed and muscle does fibrotic myopathy affect in horses?

Answer 21

Quarter horses

Semitendinosus/other hamstring muscles

Question 22

What causes fibrotic myopathy in horses?

Answer 22

Muscle tear, IM injection or neuropathy

Question 23

What is the treatment for fibrotic myopathy in horses?

Answer 23

Rest, NSAIDs and surgical resection of fibrous tissue or tenotomy

Question 24

What characteristic gait is seen with fibrotic myopathy in horses?

Answer 24

Foot slapping down on the floor

Question 25

What is atypical myopathy in horses?

Answer 25

Acute onset of severe myopathy in horses at pasture with massive CK and AST increase

Question 26

How is atypical myopathy diagnosed?

Answer 26

Muscle biopsy pre or post mortem

Question 27

What is linked to atypical myopathy in horses?

Answer 27

Toxin preventing removal of 2C segments in mitochondria which are a main source of energy and used to make ATP

Question 28

What are some suggested treatments for atypical myopathy in horses?

Answer 28

Riboflavin, carmitine supplementation and support of carbohydrate metabolism