Prevalence of polysaccharide storage myopathy in horses with neuromuscular disorders.

The research investigated how common polysaccharide storage myopathy (PSSM), an equine muscle disease, is in horses with neuromuscular disorders. It considered how the breed, sex, age, and clinical signs of the horse might affect the prevalence of PSSM.

Methodology

• The researchers from the University of Minnesota analyzed 1426 fresh frozen biopsy samples that were submitted to the Neuromuscular Diagnostic Laboratory.
• These samples were used to identify horses diagnosed with PSSM, a condition characterized by abnormal accumulation of glycogen in the muscles, and the results were compared between horses with and without histological evidence of PSSM.
• The biopsies were divided into two categories: Grade 1, which contained clusters of ordinary glycogen, and Grade 2, which contained periodic acid Schiff’s (PAS) positive inclusions, types of molecules typically resistant to amylase digestion.

Results

• Out of the total, 572 horses, or 40.1%, were identified with PSSM. The majority of these were Quarter Horse-related breeds (about 62.9%), followed by Draught breeds (11.5%), and Warmblood breeds (8.9%).
• The occurrence of exertional rhabdomyolysis (muscle damage due to intense exercise) was higher in Quarter Horse-related breeds than in Draught and Warmblood breeds, whereas Quarter Horses were less likely to display muscle atrophy compared to Draught breeds.
• Quarter Horses also displayed fewer gait abnormalities than Draught and Warmblood breeds.
• Eliminating the criteria for Grade 1 biopsies decreased the overall prevalence of PSSM to 21.7% and lowered the disease’s prevalence within each breed category.
• Despite this, the within-breed prevalence declined most significantly in breeds diagnosed less often with PSSM, such as Thoroughbreds (4.5%) and Arabians (2.5%).

Conclusions

• Polysaccharide storage myopathy is a frequent cause of neuromuscular disease, particularly in Quarter Horse-, Draught-, and Warmblood-related breeds.
• The use of granular glycogen as the sole diagnostic criterion may increase the sensitivity of the diagnostic test, but might affect its specificity, possibly including horses of Thoroughbred, Arabian, and other breeds in the diagnosis.
• The findings suggest that PSSM should be considered a significant differential diagnosis for horses displaying signs of rhabdomyolysis, gait abnormalities, and muscle atrophy, especially those from Quarter Horse, Warmblood, and Draught breeds.