Incidence of MH Reactions
Estimated incidence MH reactions
The number of new cases of malignant hyperthermia presenting with a clinical reaction has averaged approximately 25 per year over the last 10 years. This represents an incidence of 1 in 2.4 million in the general population. However, only approximately 3 million people receive a general anaesthetic each year and so the incidence in the anaesthetic population is 1 in 120,000. The age distribution of those developing a reaction is skewed towards children and young adults, with an incidence of MH in children having general anaesthesia of 1 in 20,000 – 50,000.
These data are based on referral patterns to the Leeds MH Unit (national referral centre) and are similar to epidemiological data from other countries.
Estimated prevalence of MH susceptibility
Based on the incidence of MH in children (the age group with highest incidence), the likelihood of a child with MH susceptibility reacting during general anaesthesia and the number of children receiving general anaesthesia per year, we estimated the prevalence in the UK to be 1 in 8,000 – 10,000.
Using genetic data, Monnier and colleagues (Anesthesiology 2002; 97: 1067-74) in France estimated the gene frequency at 1 in 3,000. Using similar methodology, we calculated a similar gene frequency for the UK.
Penetrance of MH
By definition MH can only occur in a patient receiving general anaesthesia and then only if the triggering drugs are used. Many patients react on their first anaesthetic exposure but some have had multiple general anaesthetics without apparent problems before subsequently reacting.
The MH susceptibility phenotype, as defined by the in vitro contracture tests, is completely penetrant.