Equin Polysaccharide Storage Myopathy (EPSM)


Reprinted from The Icelandic Horse Quarterly: Issue Four 2004.
The Icelandic Horse Quarterly is the official publication of the US Icelandic Horse Congress. The magazine is printed four times annually and mailed to the membership. Back issues may be purchased for a small fee and may be read online at www.icelandics.org/quarterly.

In talking about EPSM, it is first necessary to mention equine rhabdomyolosis syndrome-most commonly known as tying up. There are two types of tying up, sporadic and chronic. Within the chronic forms of tying up there are two subtypes, one of which is the disease of EPSM.

EPSM involves excessive storage of carbohydrates in muscle fibers in afflicted horses. The disease has been confirmed in horses of many different breeds: it is most common in draft horses but is also found in Warmbloods, Haflingers, Fjords, Friesians, Quarter Horses and QH-related breeds, Arabians and ALSO Icelandics. It has been proven to be an inherited disease in Quarter Horses, coming from 3 main sire lines, but heritability has not yet been definitively proven in other breeds.

Moderate to severe cases are not hard to diagnose, but mild cases may present a series of vague symptoms that are not easily diagnosed. Because of the natural stoic nature of some breeds, by the time problems become obvious and are recognized, the disease may be quite advanced and severe. Symptoms may include poor performance, difficulty performing canter, gait abnormalities, depression, stiffness, muscle cramping and reluctance to move forward, loss of muscling, "shivers," tying up and even death. EPSM-affected horses may appear completely normal for years or may have symptoms of low-level muscle injury during exercise that are so mild that owners fail to recognize them. It is not completely understood what puts them over the edge into massive muscle injury (such as in tying up). Since the symptoms can mimic other diseases (Lyme disease, EPM, HYPP, EMND), many times the underlying problem of EPSM is not addressed.

A roughage-only diet of hay and pasture is sufficient for maintaining horses up to a moderate work level, but demands on harder-worked horses are usually met by feeding some sort of concentrated energy source. EPSM is thought to arise from an underlying inability to properly utilize carbohydrates commonly found in concentrates. The EPSM horse is left with muscles that are clogged with polysaccharide molecules that cannot be converted to energy. EPSM horses are "metabolically different" and need dietary fat to keep their muscles functioning properly.

In diagnosing EPSM, first a blood test is done looking for increased serum activities of muscle enzyme. Giving the horse 15 minutes of exercise at the trot, 4-6 hours prior to the blood being drawn, is often sufficient to produce subclinical rhabdomyolysis (tie up) in horses. Although high enzyme levels indicate an episode of tying up, this test itself does not give the reason for tying up. It is important to know that normal levels of muscle enzymes do not rule out EPSM, though. It is only when muscle breaks down that enzymes are released into the blood. EPSM muscle can be dysfunctional, weak, sore or stiff without actually breaking down and without actually resulting in a positive blood enzyme test result. Examination of a muscle biopsy confirms or denies the definitive diagnosis of EPSM. The biopsied muscles of EPSM horses show higher amounts of stored glycogen than in normal horses.

Current recommendations to prevent recurrent episodes of tying up or other problems in EPSM horses involve removing as much carbohydrate as possible from the diet and substituting oil and protein as an energy source. Typically recommended is the addition of alfalfa pellets, beet pulp or other high fiber and low starch/low sugar feed with oil in amounts depending on body weight. Usually a 1,000 pound horse should ingest 2 cups of oil per day, which works out to be about 20-25% of total daily calories. Fats such as corn oil, soybean oil or vegetable oil are typically used in the diet and are increased gradually over the course of a week or so. It is important to know that even EPSM horses that are on a forage-only diet would also need to have fats increased to the appropriate levels.

If the EPSM horse is to survive and return to usefulness, it must have fat added to its diet for the rest of its life, as well as daily exercise. It is anticipated that it could take 4, 6 or even 12 months for recovery to occur and muscles to regenerate. A small percentage of horses remain exercise-intolerant for the rest of their lives.

Resource Credit: www.ruralheritage.com


Kvittur fra Grafarkoti, my 8-year-old Icelandic gelding, exhibited symptoms that were intermittent and seemingly unrelated over a period of 2 years. The symptoms started out very slight and just occasional - you almost thought they must be your imagination. He periodically had a loss of energy; over time his enthusiasm for exercise decreased; holding his rear legs up for the farrier became increasingly more difficult; he seemed a quieter horse with some depression; there seemed to be less muscle and muscle tone, particularly in shoulders; this past summer he experienced difficulty maintaining canter quality and became heavier on the forehand with strides becoming shorter. As I look back on the last 2 years, it is easy to read these symptoms now that I have become educated about EPSM. They were noticeably increasing, especially this past spring and summer. His symptoms were investigated on at least 4 occasions by my veterinarian without coming to any definite conclusions. Blood work was done; a Thermoscan of the body and legs, flexion tests, and all other tests were "normal." In July, for lack of a diagnosis, new vitamins were prescribed, an injection of Legend was given and the use of bute to improve his comfort was suggested whenever farrier work was to be done.

I still never felt that Kvittur was as he should have been last summer, but there was never a real reason to stop his training. There was no lameness, no illness, no loss of appetite, and his blood work was normal - so training continued.

After trailering home 8 hours from the evaluations and 2 days of turnout to rest, I saddled him to trail ride. About a half hour into the ride, he began to sweat heavily and became stumbly; also, his respirations increased significantly. I dismounted and walked him home. What he was experiencing was a typical "crisis" for a horse with EPSM: this is a crisis that you can't miss even if all the other mild symptoms of the past were not diagnosed correctly.

Through information from a friend whose Warmblood also has EPSM, I began my own research on EPSM using the internet. I became more convinced of Kvittur's diagnosis, so I immediately put him on the suggested high fat, high fiber, low carbohydrate diet with the appropriate supplements and began to give him gentle daily exercise - combined with 24 hour turnout - so that additional glycogen did not accumulate in his muscles. The blood work was done and came back "high positive" for increased enzyme activity. Then I had a muscle biopsy done - a minor surgery that can be done in the barn. The specimen was sent to Dr. Beth Valentine, DVM, PhD, University of Oregon, Veterinary Pathology Department, who read the biopsy. It came back positive for EPSM.

There is little else that can be done for Kvittur except to follow the prescribed diet and exercise program for the disease of EPSM. Right now, his exercise consists of walking with a little trotting as I visually monitor him for signs of muscle cramping. Sometimes he is hand walked and sometimes ridden slowly so I can better feel what is going on with him. I will gradually increase daily exercise as he is able to tolerate it.

There is always the chance that he will not return to his former level of usefulness, but I am trying to remain optimistic that he will make a full recovery, within a year. So far his progress has been quite slow, although steady, with only one additional tie up. Cold weather seems to be affecting his recovery, but there is no controlling that in Michigan. It can be expected that there may be a few more crises during this period while his body is adjusting to using fats for energy rather than carbohydrates. This disease is "forever," and Kvittur must always be kept on the diet and exercise program to prevent future incidents of tie up.

It is my hope that other Icelandic owners will be observant of mild and seemingly unrelated symptoms in their horses and avoid a crisis by early testing. If you go to "EPSM" on the internet you will be referred to several sites for additional information.

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