Fever of Unknown Origin (Pyrexia of Unknown Origin)

Fever of Unknown Origin (Pyrexia of Unknown Origin)
Fever of Unknown Origin was originally defined by Petersdorf and Beeson in 1961 as an illness of more than 3 weeks’ duration with fever of more than 38.3°C (101°F) on two occasions and an uncertain diagnosis despite 1 week of inpatient evaluation.
Nowadays, most patients with FUO are hospitalized if their clinical condition requires it, but not for diagnostic purposes only; thus the in-hospital evaluation requirement has been eliminated from the definition.
The definition has been further modified by the exclusion of immunocompromised patients, whose workup requires an entirely different diagnostic and therapeutic approach.
New definiton:
Fever more than 38.3°C (101°F) on at least two occasions
Illness duration ofmore than 3 weeks
No known immunocompromised state
Diagnosis that remains uncertain after a thorough history-taking, physical examination, and the following obligatory investigations: determination of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level; platelet count; leukocyte count and differential; measurement of levels of hemoglobin, electrolytes, creatinine, total protein, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, creatine kinase, ferritin, antinuclear antibodies, and rheumatoid factor; protein electrophoresis; urinalysis; blood cultures (n = 3); urine culture; chest x-ray; abdominal ultrasonography; and tuberculin skin test (TST).
Over 200 causes of FUO have been described in the literature. These causes can be subdivided in four categories:
Infective
Inflammatory
Neoplastic
Miscellaneous
Reference:
Mulders-Manders C, Simon A, Bleeker-Rovers C. Fever of unknown origin. Clin Med (Lond). 2015;15(3):280-284. doi:10.7861/clinmedicine.15-3-280
Fernandez C, Beeching NJ. Pyrexia of unknown origin. Clin Med (Lond). 2018;18(2):170-174. doi:10.7861/clinmedicine.18-2-170
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