[Fever of unknown origin: case reports from routine clinical practice and a review]

Fever of unknown origin represents a clinical syndrome characterized by a fever of over 38.3 °C documented on several occasions during a period of at least 3 weeks, etiology of which remains unexplained after obtaining a detailed history, conducting a thorough physical exam, and an array of basic laboratory tests and diagnostic imaging. Most cases of this syndrome are caused by infections, non-infectious inflammatory diseases, and neoplasms. In addition, drug fevers and internal medicine diseases should be included in the differential diagnostic work-up in all patients. This article presents five case reports of fever of unknown origin managed at an outpatient clinic of a tertiary care center for infectious diseases. This case series emphasizes the need for a consistent, broad and interdisciplinary diagnostic work-up. In addition, we present a review of the etiology and clinical management of fever of unknown origin.

Fever of unknown origin

Fever of unknown origin is a rare clinical syndrome, that represents a significant diagnostic challenge. There have been described more than 200 potential diseases, that can manifest as a fever of unknown origin. These are classically divided into following categories: infections, non-infectious inflammatory diseases, malignancies, and other miscellaneous disorders. Each of the disease type is associated with rather characteristic symptoms, clinical signs and laboratory findings, which are individually non-specific, but may provide helpful clues for a further focused diagnostic work-up. The clinicians task is to be able to identify these hallmark clinical features and to correctly interpret their significance and limitations in the appropriate differential diagnostic context. The aim of this review is to provide up-to-date clinical research evidence and to propose a  concise clue-oriented diagnostic approach.