Fever, hyperthermia, and hyperpyrexia

Fever, hyperthermia, and hyperpyrexia

It is important to understand that by definition fever, hyperthermia, and hyperpyrexia are three different entities 

Fever: Fever is a rise in core body temperature in which the set-point in the hypothalamus shifts upward from the normothermia to the febrile levels. It leads to vasoconstriction, resulting in blood divergence from periphery to the internal organs.

 Hyperthermia: This is the pathophysiology in heat stroke syndromes, metabolic dysregulations, and drugs/agents interfering with thermoregulation. The thermoregulatory center stays at normothermic levels. Body temperature increases to uncontrolled level and overrides the ability of the body to lose heat. In contrast to fever, hyperthermia can quickly become fatal. 

Hyperpyrexia: This term is used for extremely high fever (above 41.5°C). It is likely seen in brain hemorrhages.

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References:

1. Stitt JT. Fever versus hyperthermia. Fed Proc. 1979 Jan;38(1):39-43. PMID: 759237. 

2. Walter EJ, Hanna-Jumma S, Carraretto M, Forni L. The pathophysiological basis and consequences of fever. Crit Care. 2016;20(1):200. Published 2016 Jul 14. doi:10.1186/s13054-016-1375-5 

3. Hussein O, Torbey M. Hyperpyrexia as the Presenting Symptom of Intracranial Hypotension. Neurocrit Care. 2018 Jun;28(3):395-399. doi: 10.1007/s12028-017-0481-9. PMID: 29150776.

4. Singh IS, Hasday JD. Fever, hyperthermia and the heat shock response. Int J Hyperthermia. 2013 Aug;29(5):423-35. doi: 10.3109/02656736.2013.808766. Epub 2013 Jul 17. PMID: 23863046.