Fever of Unknown Origin


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)

  1. Rheumatologic/Inflammatory
  • Sarcoidosis
  • Lupus
  • Rheumatoid Arthritis
  • Giant Cell arteritis
  • PMR
  • Still’s disease
  • Vasculitis
  • Inflammatory Bowel Disease
  • Crystal induced arthritis (don’t forget about gout, pseudogout!)

2.   Infectious

  • Abdominal abscess
  • Endocarditis
  • Syphilis
  • Mycobacterial
  • Osteomyelitis
  • Tuberculosis

3. Neoplastic

  • 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
  • Leukemia

4. Others

  • Drug fever
  • Pulmonary Emboli or venous thrombosis
  • Periodic Fever
  • Thyroiditis
  • Retroperitoneal Hematomas

Evernote Link: https://www.evernote.com/shard/s338/sh/7aa15af2-1058-422a-a4f9-c7470567f768/ee0570c027aa8d06a8dc741db23b18f2


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