Fever of unknown origin. An approach for the Internist

Abstract

Fever of unknown origin (FUO) represents a diagnostic challenge for physicians, since there are multiple differential diagnoses around it and its approach is based on the distinctive clinical features of each pathology. These can be grouped into diseases whose etiology is of infectious origin, autoinflammatory or autoimmune, malignant neoplasms, and even in a large percentage of cases no apparent cause is found. Each of them is associated with characteristic symptoms, clinical signs and laboratory findings, which although not specific when analyzed individually, can be useful to establish a diagnosis and choose the appropriate treatment for the patient. The etiological classifications have remained the same since 1991, however, the initial clinical evaluation combined with current technological advances have allowed for better diagnostic performance and timely treatment. In the following, we will review recent definitions, phase-guided clinical approach, followed by new advances in nuclear medicine and metagenomics, with their respective advantages and limitations.