|Muscle samples were obtained at necropsy from 225 horses and ponies 1 year of age or older. Samples were processed in routine manner and were stained with hematoxylin and eosin and with periodic acid-Schiff for glycogen.
Sections were examined for abnormal glycogen content and amylase-resistant complex polysaccharide and for chronic myopathic change (excessive fiber size variation, increase in number of internal nuclei).
A total of 101 horses and ponies with lesions of polysaccharide storage myopathy were identified.
Age of affected horses ranged from one to 30 years, with a mean of 14.7 years. Mean age of nonaffected horses was 12 years.
Incidence of polysaccharide storage myopathy varied depending on breed; Thoroughbreds had the lowest (27%) and draft-related horses had the highest (86%) incidence.
Chronic myopathic changes were more severe in polysaccharide storage myopathy-affected horses than in nonaffected horses.
Results of this study indicate that polysaccharide storage myopathy is a common disorder of many breeds of horses and ponies.
Source: B. A. Valentine and B. J. Cooper (2005): Incidence of Polysaccharide Storage Myopathy: Necropsy Study of 225 Horses. In: Vet Pathol 42:823-827 (2005)
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