EPSM, aka PSSM, aka Equine Polysaccharide Storage Myopathy – If Your Horse Ties Up or Has Other Muscular Problems It Could Be PSSM

Unfortunately, I think my Quarter Horse mare, Corazon, has this disease. And yes, it is classified as a disease and in some cases can be fatal. It afflicts mainly draft horses, warmbloods, Arabians, and, alas, the American Quarter Horse. I’ve had Corazon less than two years, and she has always had body problems, stiffness, and a resistance to moving out–even to the point of bucking when asked to canter. Her muscles also “waste”, or atrophy, quickly if she’s undernourished or can’t move enough. I’ve been doing all sorts of things to help her (including body work), and not asking too much when riding her, but when her right rear leg recently developed a pronounced “hitch,” I sought the advice of my dear friend and holistic equine veterinarian in Texas, Dr. Madalyn Ward, and she said it sounded like EPSM. (Sob!) Dr. Ward has a Quarter Horse who she suspects may also have EPSM, so she has been paying a lot of attention to this disease lately. Her horse “ties up,” which Corazon does not, but there are many other symptoms of EPSM. The following is a guest post from Dr. Ward on how to recognize the signs of and treat this insidious, often-unrecognized disease. So far the only way a definitive diagnosis can be obtained is from a muscle biopsy. Treatment is mainly through diet. If you have a horse exhibiting any of these problems, who just can’t seem to get through them, I hope this guest article from Dr. Ward will be helpful. Although this article focuses mainly on the symptom of “tying up,” treatment is the same for all EPSM symptoms. My thanks to Dr. Ward for sharing this information.

Corazon, after a recent body work treatment that we hope is making her more comfortable.

“Tying up” is one of the most common muscular problems in performance horses, although this condition can also occur in lightly-worked horses.

Signs of acute tying up are very obvious and include:
– anxiety
– refusal to move
– swelling in muscles of the hindquarters

Chronic symptoms include:
– abnormal hind leg gaits
– exercise intolerance
– muscle wasting
– back soreness
– difficulty lifting hind legs
– behavior problems under saddle
– spasmodic type colic
– elusive lameness or behavior problems

EPSM and Horses Tying Up:
Equine polysaccharide storage myopathy (EPSM) is by far the most common cause of tying up in horses. EPSM has been around for years but now it is being recognized earlier and diagnosed much more frequently. For years I have attempted to treat frustrating cases of tying up. I now realize how many of those horses probably had EPSM, and wish I had known more about it sooner.

EPSM is a genetic disorder that affects a horse’s carbohydrate metabolism. Affected horses store too much glycogen in their muscles, which they cannot break down to produce carbohydrates. Without these carbohydrates as energy sources, these muscles lack the necessary fuel during exercise. As a result the muscles must use energy from less efficient energy pathways, which produces damaging byproducts, such as lactic acid.

Conventional Treatment of Tying Up:
Conventional treatment of acute episodes of tying up includes non-steroidal anti-inflammatory drugs, sedatives, and fluids if muscle damage is severe. Signs of severe damage would include muscle swelling, heat, and pain on palpation. The horse’s urine might also turn dark since the pigment from damaged muscles passes through the bloodstream.

Holistic Treatment of Tying Up:
Holistic support for acute episodes of tying up includes giving the homeopathic remedy Arnica every 5 to 10 minutes until the horse is relaxed and able to move. Gentle body work such as TTEAM, Bowen, or Equine Touch can bring more circulation to the tight muscles. Rescue Remedy can be used to help the horse relax.

Early Recognition of EPSM:
Early recognition of the symptoms of EPSM will allow you to take steps to manage the horse so that tying up never happens. Arabians, Quarter Horses and Warmbloods are the most commonly-affected breeds, but any horse with chronic back soreness or unexplained hind limb lameness should be considered for EPSM. A muscle biopsy can confirm the condition, but often a horse’s response to diet and management changes will provide a good indicator. Horses with EPSM should not be confined to a stall. Movement is very important. A low starch, high fat and fiber diet is also critical for controlling the symptoms. Some mildly affected horses will respond to a formulated low starch feed and mixed alfalfa/grass hay. Others will need much higher fat levels–up to 20% of the overall diet.
Conventional wisdom suggests vegetable oil as the best source of fat for horses that require higher levels of this nutrient. I do not like vegetable oil because it is almost always highly processed and refined. Vegetable oil is also lacking in vitamins or minerals, so these must then also be supplemented to meet the needs of the horse. I prefer a low starch feed and a grass/alfalfa hay mix that is supplemented with high fat seeds such as flax, chia and/or sunflower. The seeds are much more natural to the horse’s diet and include other nutrients to meet the horses overall needs. Extruded rice bran that has added minerals can also be used as a fat source. If none of these diet plans bring the fat content high enough to control symptoms, then vegetable oil can be used up to 2 cups a day. Additional antioxidants such as coenzyme Q10, vitamin E, and selenium can help the horse more readily heal the damage to his muscles.

What to Expect:

Response to the low starch, high fat diet will take about 4 months, so you must be patient even if symptoms don’t appear immediately better. Signs of improvement include re-bulking of atrophied muscles, comfort when hind legs are raised, and freer movement of the hind end in general. Many EPSM horses will appear to have much higher energy on the new diet and this is mainly due to freedom from chronic muscle spasm.

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2 Responses so far »

  1. 1

    Christine said,

    There is a hair root genetic test available that can diagnose PSSM type 1 but not 2. It is much less invasive and more cost effective at only $35 from Animal Genetics. I suspected for years that my Paint gelding had PSSM and it was nice to have a definitive diagnosis rather then just suspicion.

    • 2

      Hi Christine – How synchronistic! I just learned about this, though about a different place, the vet lab at the University of Minnesota. I will be sending off my hair samples tomorrow or the next day. And I think this lab can diagnose both types, then they work with your vet in devising a treatment plan/diet. Apparently genetic testing for this disease is a fairly new thing, so yay for modern science! I’m really looking forward to getting a proper dx and working out the best possible diet. Thanks so much for posting this. Leta


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