Fever

Fever is an elevation of body temperature mediated by the hypothalamus in response to exogenous pyrogens and pyrogenic cytokines. Patients with acute fever should be assessed promptly for signs of sepsis. Pyrexia of unknown origin (PUO) is defined as a fever ≥38.3 °C on several occasions over a period of at least 3 weeks, with uncertain diagnosis after a number of obligatory tests. A diagnostic algorithm is outlined in which the most important steps are a thorough history and physical examination, with investigations in a search for potentially diagnostic clues. Scintigraphic methods, such as 67gallium citrate, labelled leucocytes and 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET), are often used in PUO. The favourable characteristics of FDG-PET/computed tomography mean that conventional scintigraphic techniques are being increasingly replaced by this technique where PET is available. Most patients with undiagnosed PUO have benign self-limiting or recurrent fever.