Equine polysaccharide storage myopathy.

The research discusses the frequency of equine polysaccharide storage myopathy (EPSM) in UK horses, disagreeing with a previous comment suggesting that EPSM is not a common cause of the equine rhabdomyolysis syndrome in the country. EPSM is not infrequently diagnosed in horses that tie-up, and could be more frequent than suspected due to under-diagnosis. The paper also discusses the diagnostic techniques for EPSM, stress on biopsy process, and the implications of this previously under-recognized disease for the health of horses in the UK.

Evidence of EPSM in UK Horses

• The authors disagree with the assertion that EPSM is an uncommon cause of equine rhabdomyolysis syndrome in the UK. This assertion was disproved by the number of pathology service submissions from horses with a history of ‘tying-up’, as well as horse specimens from different regions.
• The authors also observed EPSM in Appaloosas, diagnosing this muscle disease in two additional horses of this breed presented to the Royal Veterinary College’s (RVC) equine hospital.
• The authors posit that EPSM may be more prevalent than currently suspected, as many veterinarians do not routinely conduct muscle biopsies on horses exhibiting symptoms of ‘tying-up’.
• Although the prevalence of EPSM seems low among purebred Thoroughbreds, the authors believe that many UK competition and pleasure horses with Draught or Warmblood breeding, which are prone to EPSM, inflate the prevalence.

Diagnosis of EPSM

• The authors highlight that diagnosing EPSM via histological examination of muscle biopsy specimens mandates an experienced pathologist.
• They clarify that muscle glycogen increase, though present in EPSM, is not unique to the disease, occurring also in other horse muscle illnesses and species.
• They contest the notion that EPSM diagnosis can be performed by a few laboratories only. Instead, the only prerequisite is the submission of a specimen from the semimembranosus or semitendinosus muscles.
• They reference the staining method for distinguishing EPSM and stress on the requirement of a fresh PAS stain.

Implications of Research and Future Directions

• EPSM’s frequency in the equine population dealt by the RVC hospital and the authors’ success controlling such cases through diet modifications underscore the disease’s significance in the UK. This necessitates acknowledging EPSM’s impact and investigating potential familial connections.
• Following their first official EPSM reports in the UK, the authors encourage further submissions of both clinical cases and biopsy specimens for continued investigation of the disease.