Malignant hyperthermia is seen mostly in swine, but it has also been reported in dogs, cats, and horses. This syndrome is characterized by abnormally high body temperature, muscle rigidity, a very rapid and irregular heartbeat, increased breathing rate, bluish tinge to skin and mucous membranes, unstable blood pressure, fluid buildup in the lungs, impaired blood coagulation, kidney failure, and death.

Malignant hyperthermia is consistently triggered in susceptible animals by excitement, apprehension, exercise, or environmental stress. Giving certain anesthetics or specific drugs that affect the neurologic and muscular systems also consistently triggers malignant hyperthermia in these animals.

Diagnosis is based on the development of signs in an animal that has been given an anesthetic agent or is participating in a stressful event. Signs can develop slowly or rapidly. Signs include muscle stiffness, twitching, a rapid heartbeat, and an increased breathing rate. Animals that are not under anesthesia may show open-mouthed breathing and an increased breathing rate, followed by a temporary break in breathing. Blanching and redness of the skin followed by blotchy blue tinges can be seen in light-colored animals. Body temperature increases rapidly and can reach 113°F (45°C).

Usually, malignant hyperthermia episodes occur suddenly and are severe. If the condition is recognized early in an animal under anesthesia, supportive measures may be able to save the animal. Unfortunately, regardless of treatment, malignant hyperthermia is usually fatal.

Stress must be minimized to prevent malignant hyperthermia episodes in individual animals. If a cat that is suspected to be susceptible to malignant hyperthermia (or that has survived a previous episode) needs anesthesia and surgery, certain precautions should be taken. These include administering a drug called dantrolene 1 to 2 days before anesthesia and avoiding certain anesthetic agents.

Last full review/revision July 2011 by George M. Barrington, DVM, PhD, DACVIM; David L. Evans, BVSc, PhD; Don A. Franco, DVM, MPH, DACVPM; Katharine F. Lunn, BVMS, MS, PhD, MRCVS, DACVIM; Donald C. Sawyer, DVM, PhD; Jean A. Hall, DVM, PhD, DACVIM; Sharon J. Spier, DVM, PhD, DACVIM; Ivan W. Caple, BVSc, PhD, MACVSc, MRCVS