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Atypical Myopathy

Also known as 'Sycamore Poisoning' Atypical Myopathy is a potentially fatal disease of horses and poneys within the UK and Northeren Euurope. Although little is known about this condition it is thought to be caused by consuming sycamore Seeds, seedlings and the leaves. With prompt intensive veterinary treatment horses can make a full recovery. however, those that are severely effected often die.

Atypical Myopathy Results in muscle damage and in particular the muscles that enable the horse to stand. It also effects the cardiac muscles and those that allow the horse to breathe. As a result of the damage, horses can display a wide range of symptoms. These can include:


  • Muscle Soreness

  • Muscle Tremors

  • Fast and laboured breathing

  • weakness

  • choke

  • head tossing or low head carrriage

  • Whinnying

  • Reluctance to work

  • Red or brown urine

  • stiffness

  • lethargy

  • Fast or irregular heartbeat

  • sudden Death

Atypical Myopathy is diagnosed after a full clinical examination as well as gathering information about the horses most recent grazing history. The horses gums will often be abnormally red or purple and the body temperature will be lower than normal. The degree of muscle damage can be confirmed by a blood test where the leves of enzymes, such a Creatine Kinase. This componant is released from the damaged muscle cells. Premature sampling may not show the extent of the damage due to the time it takes for these levels to peak.








                                                                                                    One of the key signs of Atypical Myopathy is the presence of dark red or brown urine.


The dark coloured urine is due to the prescence of Myoglobin that is released from the damaged muscle cells, into the blood and then removed from the blood stream by the kidneys. This disease is one of very few that cause this to occur, coupled with grazing near sycamore trees it is as clear indication that the horse has the disease.

The most commn misconception is that the disease will always result in death. However the survival rate is 50:50 so it is vitally important that the treatment starts immediatly. Horses showing mild signs are still at risk and transport to an equine hospital should be highly considered.  Often horses will get worse for a period  of 24-48 hours before they start to show an improvements.


Fluid therapy provided via intraveinous drips is essential to help protect the kidneys from irreversable damage. This is can only be achieved via hospitilastion where the horse will receieve round the clock nursing. Fluid therapy is also important to help prevent dehydration which is typical of this disease.  As the disease progresses the horse will become increasingly more painful. Painkillers and anaesthetic drugs can be given to the horse easily whilst under intensive nursing which can not be reasonably administered elsewhere.


Mortality rates vary from year to year and can range from 40% to 100%. Most horses that are still alive after 5 days since the onset of initial clinical symptoms are likely to recover. Initial recovery is often slow, however most effected horses that do recover will go on to make a full recovery with no long-term effects of the disease.

Preventing Atypical Myopathy requires some thought as it is not as simple as giving a vaccine. At present the only known source of the toxin that causes the disease is from Sycamore seeds and potentially the leaves too - Although the leaves to bear a lesser risk. Every UK case has been linked to the European Sycamore. Other members of the Acer family are often a cause for concern with horse owners. Thorough investigations of all tree species are yet to be performed, but initial findings show some other North American and Japanese Acers that are generally only grown as garden trees and shrubs can produce the same toxins.


If your fields are close to European Sycamore trees there are a few precautions that you should consider following:

  • If you have a selection of fields considering using those further away from the trees at certain times of the year.

  • Check all fields carefully for the Sycamore seeds and leaves

  • Reduce the number of horses within the grazing so that there is pleanty for each animal.

  • Fence off the areas where the seeds and leaves have fallen

  • hoover/pick-up Sycamore seeds and leaves from the pasture

  • Provide additional forage so horses are not searching for food to eat out of desperation. This is especially important if the grazing is poor.

  • Turn horses out for shorter periods of time

sycamore seed atypical urine sycamore-seedlings Acer-pseudoplatamus