Epidemiology of Fever of Unknown Origin (FUO)
- Fraction of undiagnosed FUOs dropped from >75% in 1930s to <10% in 1950s. Since then, fraction of FUOs that go undiagnosed has steadily increased.
- Due to earlier diagnosis by radiologic imaging, extrapulmonary TB, solid tumors, and abdominal abscesses have become less prevalent as causes of FUO.
Utility of Acute-phase Reactants in FUO
- Not very specific, but can be helpful in extreme elevations.
- In one study, 263 patients with ESR elevations above 100 mm/h were reviewed: 58% had malignancy (most commonly lymphoma, myeloma, metastatic colon or breast cancer), and 25% had infections (such as endocarditis) or inflammatory disease (like RA or GCA). Zacharski et al., Significance of extreme elevation of erythrocyte sedimentation rate. JAMA 1967; 202(4): 264.
Differential Diagnosis for FUO (A very broad differential, but the most common culprits are included)
- Rheumatoid Arthritis
- Giant Cell arteritis
- Still’s disease
- Inflammatory Bowel Disease
- Crystal induced arthritis (don’t forget about gout, pseudogout!)
- Abdominal abscess
- Atrial Myxomas: Uncommon but present with fever in ~1/3 of cases.
- Renal Cell Carcinoma
- Solid tumors: Hepatocellular carcinoma
: other tumors metastatic to the liver
- Lymphoma, especially non-Hodgkin’s
- Drug fever
- Pulmonary Emboli or venous thrombosis
- Periodic Fever
- Retroperitoneal Hematomas