Polysaccharide Storage Myopathy

Polysaccharide Storage Myopathy


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Basic Information image



Definition


An inherited metabolic myopathy



Synonym(s)


Equine polysaccharide storage myopathy is referred to by several acronyms, depending on the researcher and laboratory (eg, EPSM, PSSM, EPSSM).



Epidemiology



Species, Age, Sex




• Horses, ponies, and mules may be affected.


• Clinical signs can appear at any age.



Genetics and Breed Predisposition


Quarter Horse, Paint Horse, Appaloosa, and Draft Horse–related breeds are at highest risk, but it may occur in any breed.



Risk Factors


Breed, diet (high in starch and sugar), limited exercise



Associated Conditions and Disorders




• Exertional rhabdomyolysis, shivers, and other abnormal hindlimb mechanical lameness


• Muscle atrophy


• Poor performance


• Back pain



Clinical Presentation



Disease Forms/Subtypes


The severe form is associated with single nucleotide polymorphism in the skeletal muscle glycogen synthase 1 (GYS1) gene.



History, Chief Complaint


Exertional rhabdomyolysis, muscle atrophy, poor performance, muscle cramping or pain, back pain, unexplained hindlimb gait abnormality



Physical Exam Findings


Tight, painful muscles or muscle atrophy; myoglobinuria associated with severe rhabdomyolysis; may be normal



Etiology and Pathophysiology




• Autosomal dominant inheritance of an as yet poorly defined metabolic defect. GYS1 mutation does not explain all EPSM cases and does not adequately explain the clinical signs.


• Increased insulin sensitivity is reported in affected Quarter Horses but not in affected Belgian Draft Horses and therefore is not likely to be an underlying cause.



Diagnosis image



Differential Diagnosis




• Other causes of rhabdomyolysis (glycogen branching enzyme defect in Quarter Horse foals)


• Selenium deficiency


• Ionophore or plant intoxication


• Pasture-associated rhabdomyolysis


• Other mechanical lameness


• Equine motor neuron disease in horses with generalized muscle atrophy


• Hyperkalemic periodic paralysis (HYPP) in Quarter Horses


• Lyme disease


• Abnormal gait caused by neurologic disease

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Polysaccharide Storage Myopathy

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