Polysaccharide storage myopathy in an Australian Quarter Horse.

The study investigates the case of an Australian Quarter Horse suffering from Polysaccharide Storage Myopathy (PSSM), a muscular disease commonly seen in Quarter Horse breeds, Warmbloods, and draft horses. This is one of the first reported cases in Australia and offers insight into the management and diagnosis of this condition.

Introduction

• Polysaccharide Storage Myopathy (PSSM) is a type of exertional rhabdomyolysis, a muscular condition that causes pain and stiffness.
• Often seen in Quarter Horses, Warmbloods, and draft horses, PSSM is characterized by the accumulation of glycogen, glucose-6-phosphate and abnormal polysaccharide levels in skeletal muscles.
• The paper examines a case of PSSM in an Australian Quarter Horse, which is significant as it’s a rarity in the country.

Case Presentation

• A 7-year-old Quarter Horse mare showed symptoms of PSSM, including abnormal gait and an episode of muscle stiffness but wasn’t initially diagnosed with the condition.
• The horse had taken regular light work and had a consistent diet of improved pasture, meadow hay, and lucerne chaff.
• Through blood biochemistry analysis, increased concentrations of AST and CK, which are markers of muscle damage, were noted, leading to a suspicion of exertional rhabdomyolysis.

Diagnosis and Treatment

• A biopsy of the horse’s muscle showed structures consistent with PSSM, leading to a definitive diagnosis.
• Management recommendations were made including dietary changes, turnout to pasture and electrolyte supplementation.
• Exercise was discontinued, and regular check-ups were suggested to monitor the horse’s condition.
• After four months of follow-up, the horse showed a good body condition with regular light work. There were no recorded episodes of muscle stiffness or lameness.

Discrepancies in Presentation and Treatment of PSSM

• Different presentations of the disease, such as back pain, muscle spasms, lameness, and colic-like signs of pain, can be observed. In this case, the horse showed minimal symptoms such as an altered gait and muscle stiffness.
• Though glycolysis is functional in horses with PSSM, glycogen accumulation reflects problems with glycogen synthesis, which is enhanced in the presence of insulin.
• Treatment and management recommendations included anti-inflammatory therapy, confinement in some cases, modifications of diet, and monitored exercise, similar to other types of exertional rhabdomyolysis.

Conclusion

• This case of PSSM in an Australian Quarter Horse highlights the need for meticulous detection, management, and monitoring of the condition.
• Increased awareness of the condition in horses showing signs of skeletal muscle dysfunction, coupled with proper diagnostic procedures, is essential for effective management.
• Especially, the breeds susceptible to PSSM development should be closely monitored.