There are two aspects to the diagnosis: the recognition of an acute episode of MH, and the identification of patients with susceptibility to MH. Susceptibility to MH is a sub-clinical condition, although patients may describe feeling uncomfortable exercising in the heat, and some patients may complain of muscle cramps.[11]

Testing for susceptibility to MH by muscle contracture testing and/or genetic screening is part of basic health maintenance for families affected by MH. There can be discordance between genetic testing and muscle contracture testing results.[6][51] For diagnostic purposes the results of muscle contracture testing should be relied upon. However, when a causative genetic variant is identified, a diagnosis of malignant hyperthermia susceptibility should be applied; in this case, muscle contracture testing is not required.[52]

com.bmj.content.model.Caption@face85a[Figure caption and citation for the preceding image starts]: Diagnostic pathway for investigation of MH susceptibility. IVCT, in vitro contracture test; MH, malignant hyperthermia; MHN (MH negative or normal), classification applied when all contracture tests are negative; MHShc, MHSh, and MHSc, classifications are applied when contracture responses to both halothane and caffeine are abnormal, response to halothane alone is abnormal, or response to caffeine alone is abnormal, respectively. *Patients who should be asked to take part in research studies of the genetic basis of malignant hyperthermiaHopkins PM et al. Br J Anaesth. 2015 Oct;115(4):531-9. Used with permission [Citation ends].

Key risk factors for MH include exposure to potent inhalation anaesthetic and/or succinylcholine (suxamethonium), known susceptibility to MH, a previous MH episode, and/or a positive family history.

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