EQUINE POLYSACCHARIDE STORAGE MYOPATHY

Equine Polysaccharide Storage Myopathy is a muscle disease most commonly associated with heavy horse breeds.

Polysaccharide Storage Myopathy (PSSM) is a dominant autosomal hereditary condition that can cause a genetic form of tying-up with muscle damage and inability to move .At least 20 breeds have been identified with Type 1 PSSM.

EPSM is a genetic predisposition to fail to digest grains properly in the horse. The result leads to damage to muscle tissue during exertion.

PSSM is a muscle disease in horses with Quarter Horse bloodlines such as Quarter Horses, American Paint Horses and Appaloosas. The American Quarter Horse Association (AQHA) has funded research into this disease since 1995 and has provided us with the opportunity to learn much about the diagnosis, cause and treatment for this disease.

Diagnosis

The three primary techniques for confirming a diagnosis of EPSM are

• Try the added fats diet therapy for 4–6 months. Remove any and all additional sugar, if possible. If the horse improves, then EPSM is a likely suspect, and the horse is 4–6 months along the road to recovery.
• As an alternative to the "fat" diet, try the addition of ALCAR (L-acetyl-carnetine) to the diet. Many people are reporting good results from this naturally occurring amino acid, which helps the body mobilize fat for energy.
• Muscle biopsy. This is a dependable, clinical diagnosis.
• Endocrine test, from a blood sample after exercise. This was the first diagnosis technique available, but is not completely reliable.

Symptoms

Muscle wasting, especially in the rear quarters

• Muscle weakness
• Gait abnormality or lameness
• Work intolerance
• Poor performance
• Rhabdomyolysis("Tying Up", "Monday Morning Sickness")
• Stringhalt
• Shivers
• A peculiar 'hitch' in a rear leg while walking
• Dis-coordination in backing
• Failure to rise after anesthesia.

Treatment

• Blanket the horse if weather is cool. Hose the horse to remove sweat if the weather is warm.
  
• Determine if the horse is dehydrated, due to excessive sweating. Pinched skin will normally spring back and saliva should be wet, not tacky.
  
• Provide fluids: small frequent sips of water. Electrolytes (potassium, sodium, and chloride) may be added to drinking water, if palatable to the horse. Plain water should always be available as an alternative.
  
• If the horse is dehydrated, intravenous fluids may be needed. Once cool, the horse may have free access to water.
  
• Relieve anxiety and pain. Your veterinarian may administer drugs such as acepromazine and flunixin meglumine (Banamine).
  
• Remove grain. Feed only hay until symptoms subside.
  
• Provide small paddock turnout once the horse walks freely, usually in 12-24 hours.
  
• Selenium supplement.
  
• Plenty of fresh water.
• Exercise to the horse's comfort level.
• Usual salt and mineral supplements.

References


Valberg SJ, Cardinet III GH, Carlson GP, and DiMauro, S. Polysaccharide storage myopathy associated with exertional rhabdomyolysis in the horse. Neuromuscular Disorders. 1993, 2:351-359
Valberg SJ. Exertional rhabdomyolysis and polysaccharide storage myopathy in Quarter Horses. American Assoc. Equine Pract. 1995;228-230.Valberg SJ, Geyer CJ, Sorum S and Cardinet III GH. Familial basis of polysaccharide storage myopathy and exertional rhabdomyolysis in Quarter Horses and related breeds. Am J Vet Res 1996;57:286-290.
Valberg SJ, MacLeay JM and Mickelson JR. Polysaccharide storage myopathy associated with exertional rhabdomyolysis in horses. Comp Cont Educ 1997;19(9)10:1077-1086.
Perkins G, Valberg SJ, Madigan JE, Carlson GP, and Jones SL. Fluid, electrolyte and renal abnormalities associated with acute rhabdomyolysis in four neonatal foals. J Vet Int Med 1998;12:173-177.
Valberg SJ, Townsend D, MacLeay JM and Mickelson JR. Glycolytic capacity and phosphofructokinase regulation in horses with polysaccharide storage myopathy Am J Vet Res 1998;59:782-785.