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Differential diagnosis of Pyrexia of Unknown Origin (PUO)

Common differential diagnoses of pyrexia of unknown origin – for doctors, medical student exams, finals and MRCP PACES

Infective

  • Bacterial (essentially any organ, in approximate order of frequency):
    • Pneumonia
    • Urinary tract infection
    • Cellulitis (or line infection)
    • ENT
    • Abdominal/pelvic abscess
    • Endocarditis
    • Meningitis
  • TB
    • Pulmonary or extrapulmonary
  • Viral
    • Gastroenteritis
    • Hepatitis
    • HIV
    • EBV
    • CMV
    • Recent vaccination
  • Parasitic
    • Malaria
  • Rare but important

 

Inflammatory

  • Vasculitides (e.g. SLE)
  • Rheumatoid arthritis
  • Crohn’s disease

 

Malignancy

  • Haematological
    • Leukaemias; lymphomas; myeloma
  • Solid organ
    • Any, especially if disseminated malignancy

 

Other

  • Thyrotoxicosis
  • Serotonin syndrome
  • Pulmonary embolus/DVT
  • Factitious

 

Click here to learn how to take a full history in pyrexia of unknown origin

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