Pyrexia of Unknown Origin

Question 1

What is the criteria for PUO?

Answer 1

): a fever of at least 38.3°C that lasts, without diagnosis, for:
• 3 outpatient visits
• 3 days in hospital
• 1 week of outpatient investigation

Question 2

Give four types of PUO

Answer 2

Classical
Nosocomial (develops in hospital)
Neutropenic (neutrophil count <500 /mm3)
HIV-associated

Question 3

Give two classifications of pyrogens and give examples of each

Answer 3

Endogenous

• cytokines
• TNF-alpha

Exogenous
- endotoxins from gram-negative bacteria

Question 4

How to pyrogens cause fever?

Answer 4

Act on hypothalamic thermoregulatory centre to reduce heat loss

Question 5

List the major disease categories which can present with PUO

Answer 5

Infection
Malignancy
Inflammatory/Collagen
Other (e.g drug fevers, sarcoid, venous thrombosis)
Undiagnosed

Question 6

Give five contemporary imaging modalities which may be used in the investigation of PUO

Answer 6

CT-PET scan
Scintigraphy
Isotope bone scan
Ventilation/perfusion scan
Radiolabelled ciprofloxacin derivatives

Question 7

Describe the role of the “therapeutic trial” in PUO patients

Answer 7

Therapeutic trial is rarely used, unless:
• Suspected Mycobacterial infection
o Trial anti-tuberculosis therapy
o Diagnosis of Mtb unlikely if no response to chemotherapy within two weeks
• Suspected vasculitis or connective tissue disorder
o Trial steroids
o Response of temporal arteritis to steroids is dramatic - usually within 48 hrs