Malignant hyperthermia vs neuroleptic malignant syndrome: trigger, onset and response

Use the history first: anaesthesia or a dopamine blocker?

Malignant hyperthermia is pharmacogenetic: a usually inherited defect in skeletal muscle calcium handling, most often involving the ryanodine receptor, is triggered by potent inhaled anaesthetics or succinylcholine. It appears in the operating room or recovery area. A patient may have had uneventful anaesthetics before, so a past safe surgery does not exclude susceptibility.

Neuroleptic malignant syndrome is linked to reduced dopamine activity, most commonly from first or second generation antipsychotics or dopamine-blocking antiemetics, and also from abrupt withdrawal of levodopa or dopamine agonists. It most often begins within the first two weeks of treatment or after a dose increase, with features building over several days rather than minutes.

Compare the early signs each nurse should catch

In malignant hyperthermia, early clues are often seen by the anaesthesia team: an unexplained rise in end-tidal carbon dioxide, jaw muscle rigidity, tachycardia and tachypnoea. Temperature can climb rapidly and may be a later sign. Muscle breakdown releases potassium and myoglobin, so watch for arrhythmias and dark urine.

In NMS, the classic group is altered mental status, severe generalised lead-pipe rigidity, high fever and autonomic instability such as fluctuating blood pressure, tachycardia and sweating. Confusion or agitated delirium often comes early. Creatine kinase is typically raised. Serotonin syndrome is a common distractor: it develops faster, usually within a day, with hyperreflexia, clonus and gastrointestinal symptoms rather than lead-pipe rigidity.

Overlapping findings and urgent nursing response

Both conditions share hyperthermia, rigidity, tachycardia, rhabdomyolysis, raised creatine kinase and risk of kidney injury. Laboratory results support severity but do not identify which syndrome is present; the exposure history does. In either case, the first step is removing the trigger: the anaesthesia team stops the volatile agent, or the prescriber stops the antipsychotic.

For malignant hyperthermia, call for help, bring the MH cart, assist with rapid dantrolene preparation and administration, begin active cooling and monitor potassium, rhythm and urine output. For NMS, hold the suspected drug and report immediately, start cooling, maintain fluids and monitor vital signs, consciousness and creatine kinase. Treatment may include supportive intensive care, benzodiazepines, dantrolene or dopamine agonists per prescriber.

Prevention and teaching for each condition

Preoperative assessment is the main prevention for malignant hyperthermia. Ask every surgical patient about personal or family problems with anaesthesia, such as unexplained high fever, muscle rigidity or death during surgery. Report a positive history to the anaesthesia team so trigger-free techniques can be planned, and teach susceptible patients to share this history before any future procedure, including dental or outpatient work.

For NMS, monitor patients starting or increasing antipsychotics, especially during the first weeks, for fever, stiffness, confusion and unstable vital signs. Dehydration, agitation and rapid dose escalation may raise risk. Teach patients and families to report fever with stiffness or confusion promptly. Restarting an antipsychotic after an episode is a specialist decision made with close monitoring.

Work through an original scenario

Hypothetical item: a patient with schizophrenia started a new antipsychotic nine days ago. He is now confused, sweating and stiff, with temperature 39.8 C and labile blood pressure. Which action is the priority? Options: give the scheduled antipsychotic dose to settle agitation, hold the antipsychotic and notify the prescriber, apply restraints, or request a muscle relaxant for tomorrow.

Holding the drug and reporting is the priority because this pattern suggests NMS. Giving the dose continues the trigger, restraints can worsen hyperthermia and muscle injury, and delay is unsafe. Preventive teaching differs too: a patient with a family history of anaesthetic reactions should tell the surgical team before any procedure so trigger-free anaesthesia can be planned.

Sources and further reading

MSD Manual Professional: Malignant hyperthermia. Triggers, ryanodine receptor genetics, onset timing, early signs such as raised end-tidal carbon dioxide and jaw rigidity, dantrolene and cooling.

MSD Manual Professional: Neuroleptic malignant syndrome. Antipsychotic and dopamine withdrawal triggers, onset in first two weeks, tetrad of features, treatment, and differentiation from MH and serotonin syndrome.

MedlinePlus: Malignant hyperthermia. Inherited nature, triggering anaesthetics, dark urine from muscle breakdown, and telling the surgical team about family history.