Fever

Fever is an elevation of body temperature mediated by the hypothalamus, as a result of prostaglandin E2 synthesis-induced 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 higher than 38.3°C on several occasions during 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 thorough history and physical examination, with investigations in a search for potentially diagnostic clues (PDCs). 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/CT mean that conventional scintigraphic techniques are increasingly replaced by this technique where PET is available. Most patients with undiagnosed PUO have benign self-limiting or recurrent fever.