How are the conditions of the differential diagnosis of fever of unknown origin (FUO) categorized?

Updated: May 17, 2021
  • Author: Sandra G Gompf, MD, FACP, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Causes of FUO may differ geographically based on regional exposures, economic development, and available diagnostic tools. For example, in developing countries, the baseline incidence of infection may be higher, whereas noninfectious inflammatory and malignant conditions are more common in developed countries.  

This article addresses FUO as approached from the lens of practitioners in developed countries; however, causes that may present from developing countries should not be missed and may be increasing with travel. Fusco et al observed the correlation of infections causing FUO in lower-medium income countries, versus neoplasias and non-infectious inflammatory diseases in higher-income nations in a systematic review of 18 case series.  The majority of papers originated from countries considered high (6 countries) and upper-medium (8 countries) income. Four papers originated from Europe, 8 from Asia, and 6 from the Middle East. The final etiologies across the board were infections (nearly 40%), inflammatory diseases (20%), neoplasia (11%), and other (6.5%).  [2]

The list of etiologic possibilities is extensive, and it is helpful to break the differential diagnoses into broader categories, such as infection, noninfectious inflammatory conditions, malignancies, and miscellaneous. 

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