Anesthesia is a term that strikes fear into the hearts of many greyhound owners and may make them hesitant to pursue necessary medical treatments requiring anesthetizing their pet. One of the origins of that fear is a condition called malignant hyperthermia (MH). Some greyhound owners may have already lost a pet to MH or know someone who has. Others may think their pet has suffered from an episode of malignant hyperthermia when in fact they have not.

MH can be triggered by gas anesthetics (as opposed to injectable anesthetics), extreme exercise, and stress. The only treatment for true episodes of MH is an intravenous injection of the muscle relaxant, Dantrolene, as well as supportive intravenous fluid therapy, immediate removal of the patient from gas anesthetics, external cooling, and respiratory support. Even with appropriate treatment, this disease can be fatal.

The difficulty in diagnosing MH is there is no clinically validated blood test for it.* Instead, a muscle biopsy can be taken and a caffeine contracture test performed on the fresh specimen. The way the muscle biopsy responds to various concentrations of caffeine is considered diagnostic for malignant hyperthermia. Given this test requires fresh tissue, it is not routinely run by most commercial laboratories. You may even find it difficult to locate a laboratory that will perform the caffeine contracture test.

A catch-22

Since a patient must first be anesthetized to collect a muscle biopsy, many veterinarians will not biopsy suspected MH animals after an episode of hyperthermia due to the risk of inducing hyperthermia. The other difficulty for making an MH diagnosis is that some greyhounds can experience significant hyperthermia (>40.5 C [105 F]) without having true MH. The same life-threatening clinical signs that occur secondary to the elevated temperatures associated with malignant hyperthermia can also occur secondary to nonmalignant hyperthermia (non-MH).