Pyrexia of unknown origin Flashcards
What temperature is considered a fever?
Above 38 degrees Celsius
What are the substances that cause the development of a fever called?
Pyrogens
Give an example of an endogenous pyrogen
cytokine
Give an example of an exogenous pyrogen
endotoxins from gram -ve bacteria
What do pyrogens act on in the body?
The hypothalamic thermoregulatory centre causing reduced heat loss
What are the 4 different types of pyrexia of unknown origin?
Classical
Nosocomial
Neutropenic
HIV-associated
Nosocomial PUO
Develops in hospital, undiagnosed after 3 days might see this in compromised patients with HAI
Neutropenic PUO
undiagnosed fever in patient with neutrophils <500/mm3
Classically seen in haematology patients who have a lower white cell count
What are the 5 main causes of a classical PUO?
Infections
Tumour disease
Inflammatory conditions
Collagen and vascular diseases
Undiagnosed – ¼ of all patients
Why might repeated examination be worthwhile when trying to work out the cause of a fever?
Symptoms of the fever are often fleeting - go away and come back
You might miss things if you only do one examination. Perhaps the patient has developed a new murmur or a rash?
Initial investigations for a fever of unknown origin?
Chest X-Ray
Urinalysis and urine microscopy
Full blood count and differential white cell count
C-Reactive Protein and Erythrocyte Sedimentation Rate (acute phase reactants)
Blood cultures taken at times of fevers - at least 3 sets
Urea, creatinine, electrolytes, liver function tests
A new murmur would lean towards which diagnosis?
Which further investigations would you do?
Endocarditis
Further investigations: echocardiography (trans-oesophageal echo)
A patient presenting with headaches would lean towards which diagnosis?
Which further investigations would you do?
Temporal arteritis/giant cell arteritis
Temporal artery biopsy
If you pick up on tropical travel in the history which further investigations should you carry out?
Blood for malarial parasites, Dengue or HIV
And bone marrow for leishmaniasis - parasites spread by the bite of phlebotomine sand flies.
Further investigations for suspected TB infection? (3)
Sputum smear
Bone marrow
Mantoux
If you detect micro haematuria then which further investigations would you do?
Auto-antibodies +/- renal biopsy for polyarteritis
Ultrasound
What do you have to be wary of in regards to immunocompromised patients presenting with an undiagnosed fever?
They may not develop the same anatomical changes from infection as ‘normal’ patients.
ie a neutropenic patient cannot produce abscesses because they don’t have the same white cell count as a ‘normal’ host
Common imaging techniques (4)
CT PET
Ultrasound
CT
Trans-oesophageal echocardiogram
You can’t always differentiate between infection and inflammation from imaging.
What might you do to differentiate between the 2?
Obtain tissue sample for culture and histology.
Bone marrow and liver are often examined as part of a blind investigation for things like Malignancy, TB, lymphoma.
Why are patients with an unknown fever rarely given a random trial of drugs?
The treatment may mask new signs/symptoms have not yet developed, that might help to reach a diagnosis.
Also, toxicity
Which disorders commonly respond well to steroid drugs?
Vasculitis - temporal arteritis usually responds within 48 hrs
Connective tissue disorder
So, steroids can sometimes be useful in diagnosis but you must be sure that using them won’t put the patient at risk
What is fabricated fever?
When a patient has a real fever but it’s self-induced.
A rare form of child abuse where a parent or carer, exaggerates or deliberately causes symptoms of illness in the child.
In adults, a common cause = self-injection of things like soap, faecal material etc
Also known as Munchausen syndrome
