Prevalence of polysaccharide storage myopathy in horses with neuromuscular disorders.
BACKGROUND
Controversy exists as to the prevalence of polysaccharide storage myopathy (PSSM) in breeds of horses and its impact on performance.


OBJECTIVE
To determine 1) the prevalence of PSSM in horses that presented with a neuromuscular disorder, as well as breed, sex and age distributions and clinical signs 2) effect of diagnostic criteria on prevalence, breed distribution and age of horses diagnosed with PSSM.


METHODS
Fresh frozen biopsies (n = 1426) submitted to the Neuromuscular Diagnostic Laboratory at the University of Minnesota were searched to identify horses diagnosed with PSSM. Horses with and without histological evidence of PSSM were compared. Biopsies were classified as Grade 1, containing aggregates of granular glycogen or Grade 2, containing periodic acid Schiff's (PAS) positive inclusions, traditionally resistant to amylase digestion.


RESULTS
Horses (n = 572 : 40.1%) were identified with PSSM, of which 62.9% were Quarter Horse related breeds (QHR), 11.5% Draught breeds (DB) and 8.9% Warmblood breeds (WB). Exertional rhabdomyolysis was more prevalent in QHR than DB and WB, whereas QHR were less likely to have muscle atrophy compared to DB. QHR were less likely to have gait abnormalities than DB and WB. The highest within breed prevalence of PSSM was in DB at 63/116, WB 58/111 and QHR 360/753. Exclusion of Grade 1 criteria decreased the overall prevalence of PSSM to 21.7% of biopsy submissions, and decreased the within breed prevalence in each breed category. The within breed prevalence decreased most substantially in the breeds less commonly diagnosed with PSSM, Thoroughbreds (4.5%) and Arabians (2.5%).


CONCLUSIONS
PSSM is a common cause of neuromuscular disease in QHR, DB and WB related breeds. Inclusion of granular glycogen as the sole diagnostic criterion may increase the sensitivity of this diagnostic test, but conversely it may decrease the specificity of the diagnosis resulting in the inclusion of horses of Thoroughbred, Arabian and other breeds.


CONCLUSIONS
PSSM is an important differential diagnosis for QHR, WB and DB presenting with signs of rhabdomyolysis, gait abnormalities and muscle atrophy.
McCue
M E
ME
Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, 1365 Gortner Avenue, St. Paul, Minnesota 55108, USA.
Ribeiro
W P
WP
Valberg
S J
SJ
D000367:Age Factors; D000818:Animals; D001706:Biopsy / Q000379:methods / Q000662:veterinary; D005260:Female; D020022:Genetic Predisposition to Disease; D006008:Glycogen Storage Disease / Q000453:epidemiology / Q000235:genetics / Q000378:metabolism / Q000662:veterinary*; D006734:Horse Diseases / Q000453:epidemiology* / Q000235:genetics / Q000378:metabolism; D006736:Horses; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009468:Neuromuscular Diseases / Q000150:complications / Q000453:epidemiology / Q000235:genetics / Q000662:veterinary*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011134:Polysaccharides / Q000378:metabolism; D015995:Prevalence; D012206:Rhabdomyolysis / Q000453:epidemiology / Q000235:genetics / Q000378:metabolism / Q000662:veterinary*; D012737:Sex Factors
D011134:Polysaccharides