EPSM (Equine Polysaccharide Storage Myopathy) page 2

An Equine Muscle Disorder

Reno showed great anxiety about having to bear weight on the hindquarters—a basic principle of dressage. He couldn’t relax under saddle, and any uneven terrain increased his distress.

Wolfe pursued answers to Reno’s problems, and he was eventually diagnosed with EPSM. EPSM is a myopathy (muscle disorder) occurring through the horse’s metabolism.

Beth Valentine, DVM, Ph.D. is the foremost researcher of EPSM, at Oregon State University, Department of Biomedical Sciences, College of Veterinary Medicine. She noted that tying up is the most obvious sign of EPSM, along with other indications. “In dressage warmbloods, other more subtle problems are more common than tying up. Some of the more common ones are unexplained hindlimb lameness (including the exaggerated ‘hike’ characteristic of shivers), back soreness, lack of muscling in the rump and topline, reluctance to go forward, stiff gaits, and difficulty developing a balanced canter.”

The horse’s muscles change, because they don’t store polysaccharides (a complex carbohydrate) normally. EPSM is a genetic defect.

“I have no doubt that this type of metabolism is inherited,” commented Valentine. “But it may be more like whether you inherit your mother’s or your father’s metabolism than a simple recessive or dominant inherited trait. This type of metabolism seems to be associated with high performance in all breeds.”

EPSM can be confused with other disorders, such as EPM, EMND, and tying up. Its muscle dysfunction differs from the clinical signs of azoturia (tying up).