Malignant hyperthermia or hyperpyrexia

**Definition:** Malignant hyperthermia is a pharmacogenetic disorder of skeletal muscle that presents as a hypermetabolic response to potent volatile anaesthetic gases such as halothane, sevoflurane, desflurane and the depolarizing muscle relaxant succinylcholine, and rarely in humans, to stresses such as vigorous exercise and heat. May be caused by a mutation in the Ryonadine Receptor 1 gene.