Recently we have seen several cases of a relatively newly discovered disease, Equine Atypical Myopathy (EAM). At Endell Equine Hospital we have been involved in the diagnosis and treatment of this distressing condition over the last five years.

EAM causes sudden disintegration of muscles (rhabdomyolysis) in horses of any age on pastures in the autumn. Clinically the horses appear quiet, stiff, reluctance to walk, depressed and can become recumbent if not seen early; unfortunately EAM has a high mortality rate (up to 90%). At Endells we have extensive experience of treating these patients and feel that with early diagnosis and intensive care patients can survive. We have produced this fact sheet for clients to explain the condition and most importantly how to recognise the clinical signs of the disorder.

Incidence

• Sporadic condition mainly in autumn, after spells of warmth, heavy rain, humidity and winds.
• Occurs in cluster areas with several horses affected on same pasture.
• Wet, boggy, leafy fields.
• Mostly affects young horses and ponies, no sex/breed predisposition but young females overrepresented.
• Animals not in training, good/bad condition.
• May occur as an outbreak with several individuals affected

Causes

• No known cause but factors including weather conditions, poor health status and certain leafy pastures may predispose.
• Dead leaves, humidity may favour growth of moulds/mycotoxins that may increase risk of EAM.
• Speculation that a toxin producing bacterium called Clostridium sordellii and bifermantans may have a role in the disease.
• Poor antioxidant status of horse may predispose horses to EAM.

Clinical signs

• Acute onset of dullness, head down, reluctant to walk, stiff legs with hindlimbs>forelimbs.
• Mild sweating especially in the pectoral region, flanks.
• Reduced appetite, water intake, urination/defecation, signs of “colic”.
• Increased respiratory rate, heart rate, gum colour from pale pink to darker pink.
• As the disease progresses the above become exaggerated with eventually recumbency, dark brown urine (muscle breakdown products) and eventually death.

Veterinary treatment

• EAM does have a very high mortality rate but early intervention can lead to recovery.
• Clinical signs described along with a blood sample can greatly increase the probable diagnosis of EAM.
• If your horse appears as above do not walk your horse and call the hospital immediately.
• The main aims of treatment include pain relief, intravenous fluids, antibiotics and husbandry for the recumbent horses.
• Antioxidants including vitamin E/Selenium, salt blocks may help.

Urine sample from a horse with EAM