Fever of undetermined origin (FUO)

Question 1

FUO, also referred to as

Answer 1

pyrexia of unknown origin (PUO), has the following criteria:

• illness for at least 3 wks
• fevers >38.3°C (100.9°C)
• undiagnosed after 1 wk of intensive study

Most cases represent:

• unusual manifestations of common diseases
• and not rare or exotic disease

Question 2

Common examples of each group selected

Answer 2

Infection (40%)

Bacteria, e.g.

• pyogenic abscess (e.g. liver, pelvic)
• urinary infection
• biliary infection (e.g. cholangitis)
• infective endocarditis
• chronic septicaemia
• tuberculosis
• osteomyelitis

Viral, rickettsial, Chlamydia, e.g.

• Epstein–Barr mononucleosis
• cytomegalovirus
• Q fever
• HIV virus infection (AIDS, ARC)

Parasitic

• malaria
• toxoplasmosis

Malignancy (30%)

Reticuloendothelial

• leukaemia
• lymphomas

Solid (localised) tumours, e.g.

• kidney
• liver
• lung
• sarcoma

Disseminated

Immunogenic (20%)

Drugs

Connective tissue diseases/vasculitides, e.g.

• rheumatic fever
• systemic lupus erythematosus
• polyarthritis nodosa

Sarcoidosis

Inflammatory bowel disease, e.g. Crohn

Factitious (1–5%)

Remain unknown (up to 20%)

Question 3

FUO patients in need of further investigation include

Answer 3

infants <3 months

children with fever > 40°C

adults > 50 years

those with diabetes

immunocompromised

travellers

Question 4

Investigations

Answer 4

haemoglobin, red cell indices and blood film

white cell count

ESR/CRP

chest X-ray and sinus films

urine examination (analysis and culture)

routine blood chemistry

blood cultures

Other investigations are based on the clinical picture.