Tuesday 15th of June 2021
Vet Advice

Equine Atypical Myopathy

Equine atypical myopathy is a debilitating condition which is often fatal with a survival rate of approximately 20%. The condition results in the destruction of skeletal muscle and often the muscle of the heart and diaphragm. Outbreaks tend to be seasonal, with most cases occurring in the autumn.

Symptoms include

–  Dark coloured urine

–  Muscle stiffness/ weakness unrelated to exercise

–  Muscle tremors

–  Lethargy

–  Some cases show colic like symptoms

–  Choke like retching neck spasms

–  Frenzied vocalisation

–  Vigorous head shaking / nodding

–  Lying down unwilling to stand but eating.

The initial symptoms can progress rapidly with many cases developing difficulties in eating and breathing, heart problems and the inability to stand up.


The current theory for this disease is related to work carried out by researchers at the University of Minnesota identified a link between the disease and the Box Elder tree (Acer negundo), which is found in the United States. More recently it has been demonstrated that the same toxin found in the Box Elder tree (known as Hypoglycin A) is also found in the European Sycamore tree (Acer pseudoplatanus), and this is thought to be the cause of the majority of cases seen in the UK.




Prevalence and risk factors

Despite not knowing the exact cause of EAM, certain factors have been identified

–  Horses out at pasture

–  Youngstock < 3 years are most at risk (although can affect adults)

–  Horses in poor condition (although can affect any horse)

–  Unwormed and unvaccinated horses

–  Bare pasture, containing a stream/river, accumulation of dead leaves

–  Mainly seen in spring and autumn

–  Sudden adverse change in weather (change in conditions from dry to damp).


This is based on clinical signs and routine blood tests revealing critically elevated muscle enzymes (CPK and AST).


Treatment is supportive and includes intensive intravenous fluid therapy, anti-inflammatories, painkillers, multivitamins, vitamin E and is generally more successful when treated in the early stages.


–  Section off areas around sycamore trees and collect and dispose of leaves safely away from horses

–  Remove young sapling plants

–  Fence off wet areas

–  Ensure you check your horse regularly at least twice daily

–  Be vigilant of the potential signs of this disease and act quickly if your horse becomes poorly.

–  Limit turnout. Ideally stable horses over night (October- December)

–  Supply extra hay or haylage in field.

If your horse is showing any symptoms of Atypical Myopathy it is imperative that you call your veterinary surgeon as soon as possible.


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