Atypical myopathy

Question 1

What are the predominant cell types affected by atypical myopathy?

Answer 1

Type 1 muscle cells and cardiac muscle cells

Question 2

Beta-oxidation in the mitochondria in atypical myopathy

Answer 2

Hypoglycin A protoxin

-> Conversion to MCPA-CoA

-> MCPA-CoA + FAD (irreversible inactivation)

-> oxidation of fatty acids disabled

Question 3

Clinical signs of atypical myopathy

Answer 3

• Weakness
  
  • Stiffness
  • Recumbency
  • Trembling
  • Sweating
  • Pigmentiuria
  • Dysphagia
  • Tachycardia
    
    • Tachypnoea/dyspnoea

Question 4

What can be used to differentiate atypical myopathy from other diseases with similar signs?

Answer 4

Atypical myopathy causes pigmentiuria

Question 5

Urinalysis of atypical myopathy

Answer 5

Colour
§ Atypical myopathy brown-red (myoglobinuria)
§ Very concentrated urine may appear dark brown

Dipstick
§ Haemoglobin/myoglobin positive

Question 6

creatinine kinase (CK) and aspartate transferase (AST) in atypical myopathy

Answer 6

Magnitude of CK elevation exceeds other differential diagnoses including violently colicking horses

False negatives can occur if sampled very early in disease course

Question 7

Pain relief for atypical myopathy

Answer 7

Assessing pain is challenging
§ Is the horse in pain, or just weak?
§ Is he panting from pain, or from respiratory failure?

Administer NSAIDs with appropriate intravenous fluid therapy

Consider different modes of pain relief
§ Opioids
§ Lidocaine CRI

Question 8

Fluid therapy for atypical myopathy

Answer 8

Essential component of therapy
§ To replace fluid losses
§ To reduce the impact of myoglobin on the kidneys
§ To maximise tissue perfusion

BUN concentration might be higher in non-survivors

Consider both IV and oral fluid therapy

Don’t overload with ‘shock rates’ - these horses may have cardiomyopathy!

Question 9

Oxygen supplementation for atypical myopathy

Answer 9

Intranasal oxygen is well tolerated

Correct hypovolaemia or there’s little point in supplementary oxygen

Respiratory acidosis associated with poorer prognosis

Question 10

Nutritional support for atypical myopathy

Answer 10

Atypical myopathy cases rely on less efficient carbohydrate metabolism for energy production

First, try feeding a high-fibre diet orally

If intake isn’t sufficient, try IV (minus the lipid component)

Question 11

Anti-oxidants for atypical myopathy

Answer 11

Administering anti-oxidants was associated with increased survival

Vitamin E prevents lipid peroxidation

Carnitine binds the toxin in inactive form and bonds excess substrate

Vitamin B2 supports residual acyl dehydrogenase enzyme activity