Malignant hyperthermia

A potentially lethal syndrome usually triggered by inhalation anaesthetics or suxamethonium.

The underlying genetic susceptibility is most often due to a range of autosomal-dominant mutations in RYR1.

Caused by an increase in metabolic rate driven by an increase in intracellular calcium levels in muscle.

Presents with increased carbon dioxide production, muscle rigidity, tachycardia, hyperthermia, and mixed metabolic and respiratory acidosis.

A definitive diagnosis requires testing after the acute episode has resolved. Genetic testing may be the first test performed in selected patients; it may form part of the autopsy if MH is suspected as the cause of death. Muscle contracture testing can be used to exclude susceptibility to MH.

The mainstay of treatment includes discontinuation of the triggering agent, administration of intravenous dantrolene, and restoration/maintenance of normal core temperature.

Rhabdomyolysis, acute kidney injury, hyperkalaemia, and disseminated intravascular coagulation are frequently seen.

If the diagnosis is confirmed, first-degree relatives should be contacted and testing for the condition recommended.

Malignant hyperthermia (MH) is a syndrome that typically follows exposure to potent inhalation anaesthetics and/or succinylcholine (suxamethonium) in susceptible individuals.[1]Hopkins PM. Malignant hyperthermia: pharmacology of triggering. Br J Anaesth. 2011 Jul;107(1):48-56. http://www.ncbi.nlm.nih.gov/pubmed/21624965?tool=bestpractice.com In MH susceptible patients, this exposure may produce a clinical MH episode: a dramatic increase in metabolism, which leads to critical temperature elevation and rhabdomyolysis with potential hyperkalaemia. In the absence of central core disease, susceptibility to MH is a sub-clinical condition. However, some MH-susceptible people may feel uncomfortable exercising in the heat, and complaints of muscle cramps are not uncommon.[2]Sagui E, Montigon C, Abriat A, et al. Is there a link between exertional heat stroke and susceptibility to malignant hyperthermia? PLoS One. 2015 Aug 10;10(8):e0135496. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4530942/ http://www.ncbi.nlm.nih.gov/pubmed/26258863?tool=bestpractice.com