Polysaccharide storage myopathy in the M. longissimus lumborum of showjumpers and dressage horses with back pain.

The research article focuses on a study investigating if back pain in showjumpers and dressage horses due to suspected soft tissue injuries is related to polysaccharide storage myopathy (PSSM). The study diagnosed PSSM in muscle biopsies from the M. longissimus lumborum muscle of the horses and highlighted that a biopsy of this muscle can be a useful tool in diagnosing back problems in horses when other methods fail.

Objective of the Study

• The primary objective of the research was to determine if back pain in dressage and showjumper horses, attributed to suspected soft tissue injuries, was caused by Polysaccharide Storage Myopathy (PSSM).

Methodology

• The study involved obtaining muscle biopsies (specifically from the M. longissimus lumborum muscle) from 5 showjumpers and 4 dressage horses with a history of back pain.
• The biopsies were then examined histopathologically, and in 3 of the 9 cases, also using electron microscopy.
• The observations derived from these techniques were compared with M. gluteus muscle biopsies obtained from the same horses.
• Comparisons were also made with M. gluteus biopsies from 6 Standardbreds with recurrent exertional rhabdomyolysis and 6 healthy trotters for control.

Findings

• The study found that biopsies from horses with back pain showed typical signs of PSSM, which included high glycogen levels and/or abnormal deposits of complex amylase-resistant polysaccharides.
• Similar features were also found in M. gluteus biopsies from the same horses.
• Sections of horses with rhabdomyolysis showed increased PAS stain compared with healthy horses but did not show the presence of amylase-resistant material.
• The qualitative observations from the study were validated using quantitative histochemistry (optical densities) of sections stained with PAS and amylase PAS.

Conclusion

• As a result of this study, it has been demonstrated that PSSM is present in the M. longissimus lumborum muscle of showjumpers and dressage horses experiencing back pain.
• The study’s findings suggest that taking a biopsy of this muscle can assist in diagnosing back problems in horses when other diagnostic techniques, such as clinical examination and imaging, do not provide a conclusive diagnosis.