Polysaccharide storage myopathy (PSSM) is a glycogen storage disorder in Quarter Horse-related breeds, warmblood and draft horses that show signs of exertional rhabdomyolysis. A diagnosis should be made by muscle biopsy and identification of abnormal periodic acid Schiff's positive polysaccharide inclusions in muscle fibers. Prevention of tying-up in susceptible horses involves eliminating grain and sweet feed from the ration and adding a fat supplement such as rice bran. In addition, one of the most important factors to prevent rhabdomyolysis in these horses appears to be pasture turn-out and daily exercise. Some laboratories have diagnosed polysaccharide storage myopathy solely on the basis of an apparent increase in muscle glycogen staining. This has unfortunately resulted in the application of the term PSSM to horses of a wide variety of breeds with a variety of symptoms.
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|Published - Mar 1 1998