What is the difference between recurrent exertional rhabdomyolysis (RER) and polysaccharide storage myopathy (PSSM)?
RER is characterized by a defect in the mechanism of muscle contraction. The muscle is supersensitive to certain stimuli and responds to this stimulation by remaining in a state of contraction. A similar abnormality called malignant hyperthermia is common in humans and pigs. RER is a common cause of tying-up in Thoroughbred, Standardbred and Arabian horses. RER is most prevalent in young, nervous fillies. Interestingly, training at a gallop, but keeping the horse from top speed, seems to trigger an episode. Other factors that may incite tying-up include prolonged periods of inactivity, high-grain diets, excitement, and pre-existing unsoundness. PSSM, on the other hand, is distinguished by accumulation of glycogen (a form of carbohydrate) and an abnormal form of polysaccharide (a complex carbohydrate) in muscle. PSSM primarily affects Quarter Horses and related breeds (Paints and Appaloosas), warmbloods, draft horses, and a few Thoroughbreds. PSSM can develop at a young age, frequently
