Pyrexia of Unknown Origin (PUO)

Question 1

What temperature is usually considered a fever?

Answer 1

Above 38 celsius

Question 2

What are pyrogens? What is their mechanism of action?

Answer 2

• Substances that cause fever (endogenous such as cytokines, exogenous such as toxins from bac.)
• Act at hypothalamic centre to cause reduced heat loss and therefore fever

Question 3

What systemic changes tend to accompany a fever?

Answer 3

• Raised resp. rate

- Raised heart rate

Question 4

What constitutes pyrexia of unknown origin (PUO)?

Answer 4

Pyrexia with no diagnosis made after any of:

• 3 outpatient visits
• 3 days in hospital
• One week of outpatient investigation

Question 5

What are the different types of PUO?

Answer 5

• Classical PUO
• Nosocomial PUO: develops in hospital & undiagnosed for 3 days
• Neutropenic PUO: fever in patient with neutrophil count of <500
• HIV-associated PUO: fever in HIV patient that has been present for 3 days if inpatient or 4 weeks outpatient

Question 6

What are the most common causes of PUO?

Answer 6

• Infection
• Malignancy
• Inflammatory
• No diagnosis reached

Question 7

What investigations should be conducted for PUO?

Answer 7

• Thorough medical history
• CXR
• Urinalysis
• CRP & ESR
• Blood cultures
• LFTs, urea, creatinine, electrolytes

Question 8

How can a CT PET scan be useful in diagnosing PUO?

Answer 8

• Can show cells with increased turnover / inflammation

Question 9

What would some possible treatment options for PUO be?

Answer 9

• If suspected infection (particularly Tb): antimicrobials (anti-tuberculous therapy)
• If suspected inflammation: steroids (response should be quick, within 48h)

Question 10

What is a fabricated fever?

Answer 10

• Self induced fever

eg. via self injection