Malignant Hyperthermia Background

 

Malignant Hyperthermia (MH) was first described by Dr Michael Denborough, a physician working in Canberra, in 1960. He was asked to assess a boy about to have surgery who was more worried about the anaesthetic, as ten of his relatives had died under anaesthesia, and the family thought they had an Ether allergy.

 

The first evidence of MH in New Zealand was in 1968 when a 20 year old male died during an operation on his jaw in Palmerston North Hospital. It was subsequently found that he was a member of a very large susceptible family based in the Manawatu-Horowhenua region.

This family had arrived in New Zealand in the 1840s when a whaler landed in Wellington. He quickly moved to the Hutt Valley to farm, and later to the Manawatu where he married six months later. The couple had four children and the family has subsequently grown to eight generations with at least 1500 family members documented (about 2/3 living). Another 36 families have been identified in New Zealand with susceptibility to MH.

 

The incidence of susceptible MH patients presenting for anaesthesia in the Manawatu-Horowhenua region is relatively high mainly because of this large susceptible family, and partly because of this, testing for MH susceptibility was commenced at Massey University in 1978. Testing was subsequently taken over by the Palmerston North Hospital Anaesthetic Department in 1986.

 

Interestingly, MH affects other species. A pig develops a very similar form of MH and MH has been identified in dogs, cats, horses, and even a giraffe! In 1966 a veterinarian submitted an article to the British Medical Journal entitled "Unusual reaction to Suxamethonium, Thiopentone and Halothane". This was the first description of MH in swine, which have been an invaluable source of research. Four years later Dr Beverley Britt, an Anaesthetist from Toronto, Canada, described a muscle biopsy test which has been the "Gold Standard" for testing for susceptibility to MH.

 

Five patients have developed MH reactions in Palmerston North Hospital since 1968, two died and three survived. Many other reactions have probably been prevented by the screening measures undertaken to identify patients susceptible to MH and these are described in another section.

 

Although anaesthetic drugs and agents have improved remarkably over the last twenty years, the agents most commonly used are still the most "potent triggers" of an MH reaction. While the mortality rate has reduced from 80% to less than 5% world wide, a high degree of awareness of MH needs to be maintained. For families susceptible to this disorder, it is helpful to anaesthetists to exclude susceptibility by testing.