Hyperpyrexia

Hyperpyrexia is an extreme elevation of core body temperature, typically defined as a temperature of 41.5 °C (106.7 °F) or higher. It is distinct from ordinary fever by its severity and the increased risk of life‑threatening complications. Accurate measurement of core temperature (rectal, esophageal or bladder probes) is important for diagnosis.

Causes include severe infections (particularly central nervous system infections and fulminant sepsis), heatstroke, and drug‑ or toxin‑related syndromes such as neuroleptic malignant syndrome, serotonin syndrome, malignant hyperthermia and anticholinergic toxicity. Central nervous system injury, endocrine disorders and metabolic disturbances can also precipitate hyperpyrexia.

Clinical features often include altered mental status, seizures, cardiovascular instability, dehydration, coagulopathy and rhabdomyolysis. Prolonged or very high temperatures increase the risk of permanent neurological injury, multiorgan failure and death.

Management is a medical emergency focused on rapid reduction of core temperature and treatment of the underlying cause. Measures include active external and internal cooling, airway and circulatory support, correction of fluid and electrolyte imbalances, and specific therapies for causative conditions (e.g., dantrolene for malignant hyperthermia). Antipyretic medications may be used but are often insufficient alone in hyperpyrexia. Prognosis depends on cause, promptness of treatment and degree/duration of temperature elevation.