Exertional Myopathy in Dogs

Acute exertional myopathy in dogs is a metabolic myopathy and is characterized by the following:

• myalgia

• tachypnea

• extreme distress

• myoglobinuria (in severe cases)

The pathogenesis is unknown but could involve abnormal myofiber glycogen metabolism or electrolyte abnormalities.

Acute exertional myopathy occurs mostly in racing Greyhounds and endurance racing sled dogs.

Exercise induces a series of events culminating in two key clinical signs: muscle swelling and necrosis. In severe cases, acute renal failure occurs secondary to myoglobinuria.

Diagnosis is made on the basis of characteristic clinical signs in a susceptible dog. Serum CK activity is markedly elevated, and there may be evidence of metabolic acidosis. Muscle biopsies show multifocal hemorrhage and myofiber necrosis.

Treatment of exertional myopathy consists of supportive care, including the following:

• IV fluid therapy

• body cooling

• rest

• analgesics (NSAIDs should be used with caution because exertional myopathy can cause acute kidney injury)

• muscle relaxants (eg, diazepam, methocarbamol)

Although no specific studies have been conducted to evaluate the use of muscle relaxants in dogs with exertional myopathies, diazepam and methocarbamol are well-established muscle relaxants, and standard dosing guidelines can be followed. Diazepam is typically administered at 0.5–2.0 mg/kg, PO or IV, every 8 hours or as needed (1). Methocarbamol is typically administered at 15–20 mg/kg, PO or IV, every 8 hours; however, methocarbamol dosages > 330 mg/kg, PO or IV, every 24 hours, have been used to treat mycotoxin exposure (2). Both drugs should be titrated to effect, and the treatment should continue until clinical signs resolve.

Preventive measures include the following:

• decreased racing schedule

• air-conditioned kennels

• cool baths to lower body temperature immediately after racing

The prognosis for dogs with exertional myopathy depends on disease severity.

For other metabolic myopathies in dogs, see the Overview for this chapter.