Atypical myopathy (also known as sycamore poisoning) is an acute muscle disease which is fatal in up to 75% of cases. It usually occurs in the autumn and spring after wet weather. It’s seen in horses and ponies at pasture and is associated with the ingestion of sycamore seeds and saplings containing the toxin hypoglycin A, which disrupts a horse’s metabolism, usually in the leg, breathing and heart muscles.
Patients often develop multiple organ failure, with affected individuals seeming dull and anxious and being reluctant to move or raise their head; they may be unable to stand up. They may sweat and show muscle tremors and often have an increased heart and breathing rate. Some cases may require slings to support them to stand and lift their heads. Horses who are unable to stand may become cold to the touch and urine may be orange to dark brown/red in colour.
Blood tests and urine samples are used to determine the level of muscle damage, then muscle samples can be examined to confirm muscle damage.
Atypical myopathy is often fatal and, to date, no specific cure has been established, though animals who survive longer than five days have a markedly improved prognosis. Treatment aims to limit further muscle damage, provide rehydration, restore normal energy usage in affected muscle, provide vitamins and antioxidants to the body in high doses, and alleviate pain.
Affected animals need emergency intensive care to maximize the chance of survival and to treat pain. Individuals should be moved to the nearest available stable or veterinary clinic for treatment. Additional care such as grooming and frequent human interaction is important, in particularly in horses who are unable to stand.
To reduce the likelihood of your horse contracting this disease, prevent access to sycamore trees, saplings and seeds; provide ample forage and water; give access to a vitamin supplement and salt black; and limit grazing anywhere the disease has occurred before.
– Dr Kate Maxwell BSc (Hons) BVSc MRCVS GPCert(EqP)