Pyrexia of unknown origin

Abstract

<h2>Abstract</h2> Fever of unknown origin (FUO) is now often defined as a fever higher than 38.3°C on several occasions during at least 3 weeks with uncertain diagnosis after several obligatory tests. Infection accounts for about one-third of cases of FUO, followed by neoplasm and non-infectious inflammatory diseases. No diagnosis is reached in 25–35% of cases. In patients with periodic fever, this percentage is higher. A diagnostic algorithm is proposed in which the most important steps are history-taking, physical examination and obligatory investigations in a search for potentially diagnostic clues (PDCs). First, factitious fever and drug fever should be excluded. Further diagnostic procedures should be guided by a list of most probable diagnoses. In patients without useful PDCs, certain diagnostic procedures, divided into first-stage and second-stage investigations, should be performed. If no diagnosis is reached and the clinical condition is stable, waiting for new PDCs is recommended. In patients with recurrent fever, diagnosis should comprise only a search for PDCs matching known recurrent syndromes. Scintigraphic methods such as gallium-67 citrate-labelled leucocytes and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) are often used in patients with FUO. Because of the favourable characteristics of FDG-PET, conventional scintigraphic techniques may be replaced by FDG-PET in institutions where it is available. If undiagnosed fever persists, supportive treatment with non-steroidal anti-inflammatory drugs can be helpful. Most patients with undiagnosed FUO have benign self-limiting or recurrent fever. Other therapeutic trials should be considered only in patients who deteriorate.