Malignant hyperthermia is a relatively rare pharmacogenetic disorder inherited in an autosomal dominant fashion.¹ It is triggered in previously healthy susceptible individuals by exposure to potent inhalational anaesthetic agents and the muscle relaxant suxamethonium (succinylcholine). The clinical features of a malignant hyperthermia reaction have many similarities to those of heat illness.² These include a mixed respiratory and metabolic acidosis, tachycardia, rhabdomyolysis and muscle rigidity with progressive hyperthermia. The condition acquired its name because of the high mortality of the early cases.

Exertional heat illness occurs mainly in previously healthy young men during exercise, often in hot and humid climates to which the victim is not properly acclimatised.³ Typical scenarios include military exercises undertaken by personnel recently arrived in a hot country, and long-distance races that happen to coincide with one of the first hot days of the year. In these situations, multiple cases are common. Exertional heat illness is also more likely in the obese, in the physically unfit, in the presence of concurrent viral infection, after recent alcohol consumption, in those with skin diseases preventing sweating, in those with thyrotoxicosis and in those taking a variety of prescribed or non-prescribed medicines.⁴ There are, however, sporadic cases that occur in individuals, with no obvious predisposing factors, exercising in unremarkable weather conditions. Again, these often occur in the context of military exercises or running races, but it is notable that the victim is the only person out of tens, hundreds or even thousands of others taking part to be so affected. It is these cases that arouse particular suspicion of an underlying, relatively rare, predisposing factor.

Malignant hyperthermia is caused by a defect in skeletal muscle intracellular calcium homoeostasis. Clinical diagnosis of susceptibility to malignant hyperthermia …