Fever of unknown origin (FUO) revised

Area of Science:

• Internal Medicine
• Infectious Diseases
• Diagnostic Medicine

Background:

• The classical definition of fever of unknown origin (FUO) by Petersdorf and Beeson (1961) requires temperatures >38.3°C over three weeks with no diagnosis after one week of inpatient investigation.
• Advancements in imaging and biomarker analysis constantly redefine the diagnostic landscape, making the definition of 'true FUO' a moving target.
• The true prevalence of fever with an unresolved cause (FUO) remains unknown due to these evolving diagnostic criteria.

Observation:

• This review presents a clinical case of prolonged fever initially meeting classical FUO criteria.
• The case highlights the complexities in diagnosing prolonged fever, where the etiology may or may not resolve over time.
• Discussion of current literature provides context for understanding similar presentations.

Findings:

• Classical FUO definitions may not always apply as underlying diseases are often identified.
• The dynamic nature of diagnostic tools complicates the identification of 'true FUO'.
• The prevalence and specific etiologies of unresolved prolonged fevers are not well-established.

Implications:

• A prospective study is needed to evaluate the utility of various diagnostic investigations for FUO.
• Further research will help determine the types and prevalence of underlying diseases causing prolonged fever.
• Clarifying FUO definitions and diagnostic pathways is crucial for effective patient management.