Malignant Hyperthermia
Malignant hyperthermia (MH) is a sudden and often fatal rise in body temperature which is mostly associated with induction of general anesthesia by means of certain medications. It is characterized by sudden onset of extremely high body temperature, rapid heart beat, irregular heart beat and rigidity of muscles. Malignant hyperthermia is not a disease. It is a pharmacogenetic, life-threatening hypermetabolic syndrome in genetically predisposed individuals exposed to certain anesthetic agents.
Animal Species at Risk
Malignant hyperthermia affects humans, certain pig breeds, dogs, horses, and probably other animals. The underlying defect in susceptible individuals seems to be a faulty calcium metabolism in muscles which results in typical tetany symptoms. The burst of muscular activity produces tremendous quantities of heat which overwhelm the normal compensation mechanisms of the human body, and the central temperature and feedback control mechanisms may be damaged as well. In humans the syndrome is inherited in autosomal dominant pattern.
Inherited Disorder
In dogs, malignant hyperthermia is an inherited disorder of skeletal muscle characterized by abnormally high level of carbon dioxide in the circulating blood (hypercarbia), generalized skeletal muscle contracture, irregular heart beat, and renal failure, that develops on exposure to succinylcholine or certain anesthetic agents. Autosomal dominant canine malignant hyperthermia is caused by a mutation in the gene encoding the skeletal muscle calcium release channel.
Other Causes of Malignant hyperthermia
Malignant hyperthermia can also be caused by exposure to certain toxins or extreme heat. In 1995, The National Animal Poison Control Center at the University of Illinois in Urbana recorded 8 fatal cases of hops toxicity; the victims were seven greyhounds and one Labrador Retriever mix whose ingestion of spent hops from home beer-brewing kits resulted in malignant hyperthermia, an uncontrollable fever rising as fast as 2 degrees F every 5 minutes.
Breeds at Risk
If your dog is a Greyhound or other breed with particularly low body fat, be conscious of the potential of malignant hyperthermia which should be treated immediately.
References:
1. Thermoradiotherapy and Thermochemotherapy: Volume 1: Biology, Physiology, and Physics. L.W. Brady, H.-P. Heilmann, J.C. Bolomey, P. Burgman, I.B. Choi, J. Crezee, O. Dahl, M.W. Dewhirst, C.J. Diederich, R. Felix, K. Hynynen, D.K. Kelleher, A.W.T. Konings, J.J.W. Lagendijk, D. Le Bihan, E.R. Lee, G.C. Li, M.Heinrich Seegenschmiedt, Peter Fessenden, Clare C. Vernon
2. Natural Remedies for Dogs and Cats. Cj Puotinen
3. A-Z of Dog Diseases & Health Problems: Signs, Diagnosis, Causes, Treatment. Dick Lane, Neil Ewart
4. Malignant hyperthermia. Rosenberg H, Davis M, James D, Pollock N, Stowell K. In: Orphanet J Rare Dis. 2007 Apr 24;2:21
5. Autosomal dominant canine malignant hyperthermia is caused by a mutation in the gene encoding the skeletal muscle calcium release channel (RYR1). Roberts MC, Mickelson JR, Patterson EE, Nelson TE, Armstrong PJ, Brunson DB, Hogan K. In: Anesthesiology. 2001 Sep;95(3):716-25
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