There have been 224 European cases of Atypical Myopathy or ‘Sycamore poisoning’ reported to the Atypical Myopathy Alert Group (AMAG, based at the University of Leige) so far this year (as of 15th May 2017), 9 of which have been in the UK and 2 in Ireland. We hope the following information helps to raise awareness of this often fatal disease.


What is Atypical Myopathy?

Atypical myopathy is a muscle disease caused by the ingestion of sycamore seeds, seedlings and leaves. A substance called ‘Hypoglycin A’ in the seeds/ seedlings and leaves is converted to a toxin within the body which prevents cells from utilising energy. The disease develops quickly, affects skeletal, respiratory and cardiac muscles and is often fatal.


Diagnosis & Treatment

Prompt veterinary diagnosis is vital and is made based on case history, clinical signs and sometimes blood and urine analysis which is now being offered by the Royal Veterinary College (RVC). Blood tests can also now be used to determine whether seemingly unaffected horses have consumed Hypoglycin A so that ‘preventative’ therapy can begin more quickly. As there is currently no treatment available, veterinary intervention is supportive, often consisting of pain management, fluid therapy, vitamin and mineral injections and correction of electrolyte status.

What are the signs?

If you suspect your horse or pony is showing signs of Atypical Myopathy call your vet immediately. Although signs often develop gradually, some horses may be reluctant or unable to move in as  little as 6-12 hours. Signs include:

  • Stiffness
  • Muscle soreness
  • Muscle tremors
  • Low head carriage
  • Rapid or laboured breathing
  • Fast or irregular heartbeat
  • Generalised weakness
  • Reluctance to move or work
  • Collapse and/ or recumbency
  • Red or brown urine
  • Colic-like signs
  • Sudden death

Prevention Tips

Although Hypoglycin A is known to cause Atypical Myopthay, it is not yet known whether some trees or parts of the plant (i.e. the seed vs. the leaf) are more toxic than others. It is also unclear whether the level of Hypolgyin A changes throughout the year or is affected by weather or environmental conditions.

  • Avoid turning horses on out ‘high risk pastures’, particularly during spring and autumn
  • Fence off the area surrounding sycamore trees where leaves and seeds have fallen. However in strong winds, seeds and leaves may travel distances of approximately 180m
  • Pick up/ hoover as many seeds and leaves from your pasture as possible
  • Reduce turnout time
  • Provide additional forage when grazing is sparse
  • Avoid overstocking pasture to ensure there is sufficient grazing for the number of horses
  • Once a case is suspected, remove all other horses grazing the same pasture. Discuss the possibility of having non-affected horses blood tested with your vet.
  • The RVC are now able to test leaves, seeds and seedlings to identify whether or not they contain Hypoglycin A – contact your vet or the RVC for more advice


Identifying Sycamore Seeds & Leaves

Not all trees in the Acer family contain Hypoglycin A and differentiating sycamore seeds and leaves from other harmless species such as the Acer Campestre (Field Maple) or Acer Plantanoids (Norwegian Maple) found in the UK can be challenging. Familiarising yourself with the shape of sycamore leaves, seeds and seedlings is invaluable.


Sycamore leaf*                                                  Sycamore seed*


Norwegian Maple leaf*                                                      Norwegian Maple seed*

*Images courtesy of Gunther Van Loon, Gent University

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