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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