37. Heat stroke and malignant hyperthermia

Heat stroke

Heat stroke is a medical emergency where a person has hyperthermia (40-41°C), anhidrosis and mental status alteration, possible even coma. It may be deadly; the outcome is influenced by the severity of the state and by the duration of the hyperthermia. Anhidrosis develops due to CNS damage because of hyperthermia. The lack of sweating allows the body temperature to continue to rise.

Malignant hyperthermia

Malignant hyperthermia is a life-threatening condition where a person develops hyperthermia in response to certain inhalatory anaesthetics like halothane or to depolarizing muscle relaxants like succinylcholine. It most frequently occurs during surgeries. It occurs only in people who are genetically susceptible; the inheritance pattern is autosomal dominant and involves a mutation of the ryanodine receptor, a ligand-gated calcium channel. The mutation allows more calcium to enter the muscle cells, which causes muscles to twitch and produce a lot of heat and CO2. The muscles twitches are not easily visible, but the development of malignant hyperthermia can be discovered if the patient’s pCO2 suddenly increases for no apparent reason. The condition is treated with a ryanodine receptor antagonist called dantrolene.

I remember the connection between ryanodine receptor and dantrolene as two friends called Ryan and Dan.

Neuroleptic malignant syndrome

Neuroleptic malignant syndrome is an acute, life-threatening situation similar to malignant hyperthermia that may occur after a person takes antipsychotic (neuroleptic) drugs. It occurs in approximately 15 of 100 000 people who take neuroleptics every year. It causes a severe hyperthermia with psychiatric symptoms. Treatment is by dantrolene and discontinuation of the drug.