Myopathies

Question 1

Acute exertional rhabdomyolysis

Answer 1

Seen in unfit horses

CS: stiff stilted gait, profuse sweating, pain, bilateral, myoglobinuria
Worse affected - biceps femoris, gluteals, semitendinosus and semimembranosus

Dx: elevated CK and AST

Tx: fluid therapy, ACP, NSAIDs

Question 2

Chronic exertional rhabdomyolysis

Answer 2

Racehorses - repeated episodes with minimal exercise

Draft horses and thoroughbred - 5% develop it during race season
Nervous stressed TB in training

CS: poor performance, intermittent muscle stiffness and muscle contractures

Dx: intermittently elevated CK and AST - exercising

Tx: minimise stress, warm up before exercise
Avoid high energy feeds

Question 3

Polysaccharide storage myopathy

Answer 3

Draft horses, warmbloods, quarter horses
- genetic - abnormal accumulation of glycogen in the muscles

CS: muscle stiffness, amylase resistant inclusion bodies

Management: low carbohydrate, high fibre diet

Question 4

Other causes of myopathy

Answer 4

Clostridium myonecrosis
Injection site soreness / abscess
Post-anaesthetic myopathy
Fibrotic myopathy - stringhalt 
Strangles

Question 5

Atypical myopathy

Answer 5

Horses at pasture - due to the ingestion of sycamore seeds
- storms in spring and autumn

CS: acute onset, sweating, muscle weakness and RECUMBENCY, increase AST and CK, myoglobinuria

Tx: IVFT, morphine, lidocaine CRI, paracetamol