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Atypical Myopathy- "Sycamore Poisoning"

Atypical myopathy, more commonly known as sycamore poisoning, is a serious and potentially deadly disorder of the muscles caused by consuming the seeds, leaves or seedlings of the sycamore tree.


The sycamore contains hypoglycin A (HGA) which is a toxin that affects the production of energy in muscles, especially those in the heart and muscles used for standing and breathing. This can therefore be fatal with survival rates for horses affected sitting at approximately 30-40%. There is often a spike in cases after a sudden change in weather or heavy rain as the sycamore seedlings begin to grow in the spring.


Symptoms of Sycamore Poisoning

  • Muscles weakness, difficulty standing, walking or breathing

  • Lethargy- horse appears dull or flat

  • Muscle tremors or shivers

  • Brown or red urine

Sycamore poisoning is diagnosed by your vet through lab tests and observation of clinical signs. Unfortunately, there is no antidote to the HGA toxin, but your vet can provide supportive care for your horse and administer medications to reduce the absorption of the toxins from the intestine into the blood. Sometimes, a trip to the equine hospital may be required so that your horse can be set up on a drip of fluids and anti-inflammatory drugs.


Prevention is Better than Cure

  1. · Identify any sycamore trees surrounding your yard and grazing, seeds can travel up to 200m in the wind

  2. · Remove sycamore seeds, leaves and seedlings from the grazing area, or fence off the area completely

  3. · Reduce overgrazing fields to avoid your horse foraging for leaves

Some horses are more prone to sycamore poisoning than others and levels of HGA can vary year to year so don’t assume that your fields are safe just because they are grazed every year

If you think that your horse has recently consumed sycamore seedlings and/or is showing symptoms of sycamore poisoning, call your vet immediately. The quicker sycamore poisoning s diagnosed and treated, the higher the chances of survival.

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