Atypical myopathy can be suspected when a part of or the totality of the clinical signs associated to this syndrome are present. Access to pasture (at least in the days preceding the clinical signs) is a condition sine qua non to consider the diagnosis of atypical myopathy.

    Signs present in more than 50% of cases

  • DARK COLORED URINE (93%)
  • WEAKNESS (85%)
  • STIFFNESS (83%)
  • DEPRESSED (80%)
  • INCREASED HEART RATE (79%)
  • HORSE FOUND LAYING ON THE GRASS (78%) (OR DEAD)
  • MUSCLE TREMORS (68%)
  • SUDATION (64%)
  • NORMAL RECTAL TEMPERATURE (37°C <Rectal temperature < 38.5°C; 60%)
  • RED MUCOSAE (53%)
  • Signs present in less than 50% of cases

  • DIFFICULTY TO BREATHE (49%)
  • HYPOTHERMIA (29%; Rectal temperature < 37°C)
  • ANOREXIA (i.e. the horse doesn’t want to eat; 28%)
  • DIFFICULTY SWALLOWING (23%)
  • EXACERBATED APPETITE (18%)
  • HYPERTHERMIA (11%; Rectal temperature ≥ 38.5°C)

The frequency of the main clinical features of atypical myopathy as described by the review of 354 European cases (van Galen et al., 2012)

When the aforementioned clinical signs are observed in whole or in part, call your veterinarian urgently. On the basis of additional tests, your vet can confirm the disease. The definitive diagnosis of atypical myopathy is usually made after microscopic examination of the muscle fibers of a piece of muscle taken post mortem.
The diagnosis of atypical myopathy can be confirmed also on the basis of a blood sample owing to the identification of a particular blood biochemical profile. This diagnostic test is performed only in a few specialized laboratories.

NEW

Following research that was supported by The Horse Trust, the Comparative Neuromuscular Diseases Laboratory of the Royal veterinary College of London (UK) now offer vets serum testing for the hypoglycin A toxin and its principal metabolite named MCPA-carnitine known to cause atypical myopathy. Horses affected by atypical myopathy present a particular biochemical profile in urine and blood. The laboratory also offers urine organic acid and plasma acyl carnitine profile testing to support the diagnosis. Samples need to be submitted by vets. Further details and prices can be found on the lab website.

Plant samples can also be tested for hypoglycin A. Please go the “Plant sample testing” for further information.

Since the cause of atypical myopathy has been attributed to maple trees, we have observed that all confirmed cases had the opportunity to ingest samaras (cases occurring in autumn) or seedlings (cases occurring in the spring) of sycamores.
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