What is the difference between fever and hyperthermia?

• A. Fever is caused by a regulated hypothalamic setpoint change due to infection or inflammation; hyperthermia is elevated temperature not due to a setpoint change (e.g., heat stroke).
• B. Hyperthermia is caused by infection; fever is due to heat stroke.
• C. Fever and hyperthermia are the same.
• D. Fever is a measure of body temperature lower than normal.

Answer: (A)

Fever and hyperthermia differ in how the body's temperature is regulated. Fever is a regulated rise in temperature caused by pyrogens (like infections or inflammation) that tell the hypothalamus to raise the setpoint. To reach this higher target, the body generates heat (shivering) and conserves heat (vasoconstriction). When the pyrogen stimulus resolves, the setpoint returns to normal and cooling mechanisms (sweating, vasodilation) bring temperature down. Hyperthermia, by contrast, is an actual rise in temperature due to external heat load or impaired heat dissipation, without a change in the hypothalamic setpoint; the body’s cooling mechanisms can be overwhelmed, and cooling must be applied directly (and the underlying cause addressed). Heat stroke is a classic example of hyperthermia.

So the key difference is a changed hypothalamic setpoint in fever versus a normal setpoint with unregulated heat gain in hyperthermia.