Polysaccharide storage myopathy in Morgan, Arabian, and Standardbred related horses and Welsh-cross ponies.

This research study focuses on a muscle disorder in horses known as polysaccharide storage myopathy, identifying it in horses and ponies of breeds where it is not usually found. The disorder is detected by looking for specific inclusions in muscle tissue, and can cause weakness, exercise-induced muscle damage, and in severe cases, increased time spent lying down.

About Polysaccharide Storage Myopathy

• Polysaccharide storage myopathy (PSSM) is a genetic muscle disorder in horses.
• The ailment is characterized by an excessive accumulation of glycogen-related polysaccharide inclusions within skeletal muscle fibers.
• This typically leads to symptoms such as muscle stiffness, pain, and difficulty moving after periods of rest or exertion.

Diagnostic Criteria

• Diagnosing this disease involves the identification of periodic acid-Schiff-positive, amylase-resistant inclusions. These are considered pathognomonic, meaning they are unique to and indicative of this disorder.
• The criteria for diagnosing this disorder are somewhat disputed, but these inclusions are usually a clear sign of the condition.

The Study’s Findings

• Polysaccharide storage myopathy is most commonly found in Quarter Horses, draft horses, and Warmblood breeds, but this study identified the disorder in other breeds as well.
• The study found PSSM in five horses of unrelated breeds – two Morgans, one Arabian, one Arabian x Thoroughbred, and one Standardbred.
• Two Welsh cross ponies were also found to have the disease.
• Moreover, the horses affected showed histories of recurrent exertional rhabdomyolysis, a condition causing muscle breakdown due to extreme physical exertion.
• One horse developed progressive weakness, leading to a rise in recumbency time, which means that the horse spent significantly more time lying down due to weakness.
• The ponies found with the disorder were part of an unrelated research project and displayed no noticeable symptoms.

Implications of the Study

• The findings expand the common perceptions about which horse and pony breeds can suffer from PSSM, suggesting the need for a broader approach to awareness and diagnosis.
• The absence of symptoms in the Welsh cross ponies indicates that the disease can be asymptomatic, highlighting the importance of regular checks in maintaining the health of horses and ponies.