Fever of Unknown Origin

Synonyms

Fever of obscure origin; Fever of unexplained origin; Fever of unknown origin; Pyrexia of unknown origin

Definition

Fever of unknown origin is a clinical syndrome of fever that does not resolve spontaneously within 3 weeks and the cause remains unknown after extensive workup. Fever is defined as an elevation of the body temperature that exceeds the normal daily variation. The hypothalamus controls the body temperature and a normal body temperature is ordinarily maintained because the hypothalamic thermal regulatory center balances the excess heat production derived from metabolic activities in the muscles and the liver with heat dissipation from the skin and lungs. Normally, healthy adult individuals have a mean oral temperature of 36.8°C ± 0.4°C. The temperature is a little bit higher in the evening. Fever of unknown origin is an important clinical challenge. In 1961, Petersdorf and Beeson [1] defined it in their first report as an illness characterized by fever of more than...