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Increase in reported cases of Atypical Myopathy

Article posted on 24-10-2014

Please be aware that we are seeing a rapid increase in the number of cases of Atypical Myopathy (ATM) in the last week – we are aware of up to 20 cases throughout Ireland in the last two weeks. There is a similar spike being seen in the number of cases in the UK.
Please take the time to understand the symptoms and risk factors of the disease.

ATM is a severe muscular condition that affects horses at pasture, usually in the autumn and is often fatal. One or more horses can be affected, but equally co-grazers can be totally unaffected. One of the key factors in ATM was recently found to be a substance called hypoglycin found in the seeds of Acer trees such as the sycamore. Sycamore seeds are very easy to recognise and are often informally called “helicopters”.


Most frequently reported clinical signs include: sudden, unexplained onset of muscle stiffness, weakness, altered gait, rapid heart rate, laboured breathing, sweating, bladder distension, pigmenturia (blood in urine), muscle fasciculations, and horses lying down unable to get up again. These signs generally present for 12 to 72 hours, and there is a 75-90% mortality rate. Clinical cases are often initially diagnosed as colic.

The presence of sycamore trees however does not automatically mean the problem will occur. Factors such as the weather conditions, access to and ingestion of the seeds at the appropriate time of the year and the presence of sufficient levels of hypoglycin in the seeds are at required for ATM to occur.

However, the recent dip in temperature and the high winds are thought to have contributed to the high numbers of seeds currently present in pastures, which appears to be leading to a spike in the number of reported cases of ATM. Early diagnosis and treatment can increase the chances of survival. A simple blood test can confirm whether a horse is suffering from ATM. Elevated serum creatine kinase (CK) and aspartate aminotransferase (AST) are markers of the muscle damage associated with ATM.

If you have any concerns or questions about ATM please contact Dr. Ursula Fogarty at the Irish Equine Centre on 045 866 266.