
Harrison's PodClass: Internal Medicine Cases and Board Prep Ep 180: A 64-Year-Old with Fever
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Jan 22, 2026 A deep dive into fever of unknown origin and unexplained inflammation. They walk through modern criteria, baseline testing, and when a case truly qualifies. Geographic differences in causes and the FUO paradox get attention. The conversation covers diagnostic strategies, value of second opinions, and when therapeutic trials may be considered.
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Modern Definitions Of FUO And IUO
- FUO now requires ≥3 weeks of fever and exhaustive outpatient testing before labeling a case as FUO.
- IUO matches FUO criteria but uses elevated CRP/ESR instead of fever for diagnosis.
Geography Shapes FUO Causes
- Geographic region strongly shifts FUO causes: infections dominate non-Western cohorts.
- Mycobacterium tuberculosis accounts for up to half of infectious FUO cases outside Western nations.
Noninfectious Causes Predominate In The West
- In Western cohorts non-infectious inflammatory diseases are the leading FUO causes.
- These include autoimmune, autoinflammatory, granulomatous diseases, and vasculitides.








