Discussion of polysaccharide storage myopathy (PSSM) on four cases

Polysaccharide storage myopathy (PSSM) is characterized by abnormal polysaccharides and increased glycogen storage in the musculature of affected horses, which are predisposed for recurrent exercise-induced myopathies. A familial predisposition for PSSM has been reported in American Quarter Horses (AQH) and related breeds. Two AQH and a Swiss Warmblood were presented to us for recurrent rhabdomyolysis and one Haflinger for severe exercise intolerance. The signalment, clinical examination, and serumactivity valves of CK, ASAT and LDH before and after an exercise test lead to the tentive diagnosis of PSSM, which was confirmed by the histopathological evaluation of muscle biopsies. Increased muscle glycogen and pathognomonic, PAS-positive amylase-resistent polysaccharides were present in all the cases. Our report illustrates that PSSM must be included in the differential diagnosis of exercise induced recurrent myopathies in AQH as well as in horses of other breeds in Europe.