WHAT IS ATYPICAL MYOPATHY?
Atypical Myopathy (AM) is a serious and potentially life-threatening disease caused by horses ingesting sycamore seeds, seedlings, or leaves that contain a toxin called hypoglycin A. Once ingested, this toxin causes severe muscle damage, affecting the horse’s ability to move, breathe, and maintain normal bodily functions.
HOW MUCH DOES A HORSE NEED TO INGEST TO BE AFFECTED?
Unfortunately, there is no simple answer.
Not all sycamore trees contain the same levels of toxin, and concentrations can vary significantly between trees and from year to year. As a result, there is no known “safe” amount of sycamore material that a horse can consume.
Fortunately, sycamore seeds and seedlings have a bitter taste, and horses generally avoid eating them when sufficient grazing or forage is available. However, young horses can be more inquisitive and may be at greater risk of consuming them.
If you are concerned about sycamore contamination in your paddocks, samples of seeds, seedlings, and leaves can be tested for hypoglycin A. The Royal Veterinary College offers testing services for horse owners wishing to assess the risk on their land.
WHAT ARE THE CLINICAL SIGNS?
Signs of atypical myopathy can develop suddenly and may include:
- Depression and lethargy
- Weakness
- Muscle tremors
- Stiffness or reluctance to move
- Rapid of irregular heart rate
- Dark red or brown urine
- Difficulty breathing
- Colic-like symptoms
If you notice any of these signs, particularly during periods when sycamore seeds or seedlings are present, veterinary attention should be sought immediately.
HOW IS ATYPICAL MYOPATHY DIAGNOSED?
Diagnosis is based on a combination of:
- A history of access to sycamore trees, seeds, seedlings, or leaves
- Compatible clinical signs
- Blood tests showing evidence of muscle damage
Additional blood and urine tests can be performed to detect the presence of the toxin and help confirm the diagnosis.
HOW IS IT TREATED?
Unfortunately, there is currently no specific cure for atypical myopathy. Treatment focuses on intensive supportive care and nursing.
This may include:
- Intravenous fluid therapy
- Pain relief
- Nutritional and vitamin supplementation to help limit ongoing muscle damage
- Careful monitoring and supportive nursing
Early recognition and aggressive treatment are crucial. The chances of survival depend largely on the extent of muscle damage that has already occurred by the time treatment begins.
For severely affected horses, the prognosis remains poor, with survival rates reported between 10% and 25%.
HOW CAN I PREVENT ATYPICAL MYOPATHY?
Prevention focuses on reducing exposure to sycamore seeds, leaves, and seedlings.
Practical steps include:
- Fencing off areas around sycamore trees
- Regularly clearing paddocks of seeds and seedlings
- Providing supplementary hay when grass is sparse
- Removing sycamore trees from grazing areas where possible
- Monitoring fields closely during autumn and spring, when the risk is highest
Remember!
Sycamore seeds, often known as “helicopters”, can travel surprisingly long distances. They may be found up to 200 yards from the parent tree, so neighbouring trees can still pose a risk even if there are no sycamores within your paddock.
EARLY ACTION SAVES LIVES
Atypical myopathy is a veterinary emergency. Prompt recognition of the signs and immediate treatment provide the best chance of survival. If you suspect your horse may have ingested sycamore material or is showing any of the signs listed above, contact us without delay.