Rhabdomyolysis in Horses:

• Sporadic Tying Up
• Equine Polysaccharide Storage Myopathy (EPSM),
• Polysaccharide Storage Myopathy (PSSM)
• Exertional Rhabdomyolysis

  by Robert N. Oglesby DVM

Tying up is a term for horses that are suffering from a generalized muscle soreness and stiffness and medically is known as rhabdomyolysis. Though there are many causes, in most cases some metabolic event is interfering with the normal function of the muscle cell, usually the conversion of chemical energy to support normal cell function. As the muscle cells ability to convert stored energy to action grows the cell malfunctions and the result is pain and stiffness. In severe cases the celll can die and is the meaning of the term "rhabdomyolysis": death of skeletal muscle.

Horses with rhabdomyolysis first develop pain and stiffness in the larger muscle groups like those of the lower back, pelvis, and thigh region. There are some causes of tying up that effect primarily the muscles of the neck and front legs however. The problem can vary from a transient trembling or cramping to a serious problem with large amounts of muscle locked up.Severely effected horses can have remarkable muscle necrosis which can lead to kidney failure and death.

Though symptoms are similar, conditions that cause a horse to tie up include: exertional stress, nutritional deficiencies, plant toxins, and genetic defects of carbohydrate metabolism. Two examples of the genetic diseases are Polysaccharide Storage Myopathy (PSSM) in Quarterhorse, Apps, and Paints and Equine Polysaccharide Storage Myopathy (EPSM) in the draft breed. Recognition of the specific problem leading to the tying up episode has led to more effective treatment and management options and a better prognosis.

This article discusses the different causes, diagnosis, treatment, and prognosis of the different causes of tying up in horses. Links to articles on specific diseases are also provided.