4. Pyrexia of unknown origin

Question 1

Define pyrexia.

Answer 1

Fever:

• elevation of body temperature above normal (37C)
• variation of up to 0.8C daily (circadian rhythm): low in early morning, high in early evening
• Part of the systemic inflammatory response syndrome (SIRS)
• Fever considered significant if above 38C.

Question 2

Define pyrogens.

Answer 2

substances which cause fever
- endogenous e.g. cytokines
- exogenous e.g. endotoxins from G-ve bacteria
act at hypothalamic thermoregulatory centre to cause reduced heat loss and hence fever.

Question 3

How is pyrexia of unknown origin diagnosed?

Answer 3

Modern definition: No diagnosis after

• 3 outpatient visits or
• 3 days in hospital or
• One week of outpatient investigation
  i. e. prolonged fever without any diagnosis.

Question 4

Name different types of PUOs (pyrexia of unknown origin).

Answer 4

1. Classical PUO
2. Nosocomial PUO: develops in hospital, undiagnosed after 3 days e.g. healthcare related infection in compromised patients.
3. Neutropenic PUO: undiagnosed fever in patient with neutrophils <500/mm3 e.g. seen in haematological patient.
4. HIV-associated PUO: fever in a patient with HIV infection - present and undiagnosed for more than three days in an inpatient or four weeks in an outpatient.