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Autumn Dangers - Atypical Myopathy

It is around this time of year that we would like to remind our clients about the potentially fatal disease, atypical myopathy, and especially since there has been a number of cases in the equine press recently. Here, St David's vet Claire provides an overview of what causes it and what to look out for..

Atypical myopathy (sycamore seed toxicity), is a severe and often fatal disease caused by the consumption of sycamore seeds, leaves or seedlings. The disease is most frequently seen in the Autumn, but we see a spike in cases again in the Spring. Affected horses have a 20-30% survival chance, even with rapid diagnosis and treatment.

The toxin Hypoglycin A is the causal agent of atypical myopathy and has been found within the seeds and seedlings of some species of trees within the Acer family – most commonly the sycamore tree. After ingestion, the toxin prevents normal energy production in muscle cells, resulting in severe muscle damage. Often atypical myopathy will affect an individual horse, but several horses within a group can be affected. Some horse are more sensitive to the toxin than others, youngsters seem more susceptible. Horses who are out at pasture with no supplementary feed are also at a higher risk. Those horses who are in better body condition and receive regular routine care, such as vaccinations and worming, seem to be at a lower risk.

Clinical signs of atypical myopathy:
• Weakness – in the earlier stages, affected horses will have a stiff gait and struggle to walk, as the condition progresses, the horse will struggle to stand, may become recumbent and will have progressive difficulty breathing.
• Horses will struggle to lift their heads and will have a dull
• Muscle fasiculations (trembling) and sweating.
• Fast or irregular heart beat.
• Colic signs – often affected horses will retain their appetite.
• Brown or dark red urine.

• A diagnosis of atypical myopathy is often made based on clinical signs and measuring levels of enzymes in the blood which indicate severe muscle damage.

• Horses suffering from atypical myopathy require immediate intensive treatment and critical care; it is often most appropriate to take your horse to a specialist facility rather than attempting to manage at home.

• The first few days are critical for horses suffering from atypical myopathy. If they survive these initial days, then often they go on to make a full recovery in time.

If you suspect your horse may be affected, emergency veterinary attendance is required. While you are waiting for the vet, please do not force your horse to walk anywhere. Please put them in a well bedded stable, offer them fresh water and hay and put on a breathable rug. If you see your horse urinating, please collect a sample if possible for the vet to assess.

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