Pyrexia of unknown origin

35. Pyrexia of unknown origin




Questions


image What is meant by fever of unknown origin?

image Which investigations are useful?

image What are common causes?


Definition and clinical presentation


Pyrexia or fever of unknown origin (PUO or FUO) is difficult to investigate because the patients have few signs and symptoms; consequently, the list of differential diagnoses is large and the need for investigation correspondingly greater. Three features define PUO:


image an illness of more than 3 weeks in duration

image a temperature greater than 38.3°C (101°F) on several occasions

image no specific diagnosis after a week of investigations.

There are over 200 reported diverse causes of PUO, which vary slightly according to age. As immunosuppressed patients have a different spectrum of causes than immunocompetent hosts, PUO can be subclassified by type of immunosuppression:


image neutropenic

image nosocomial

image HIV associated.

Investigation is expensive both in time and resources, and it is important to ensure that the patient does indeed have a pyrexia and that it is not a factitious fever. Body temperature is normally higher in the evening than the morning, but some healthy individuals have an exaggerated circadian temperature rhythm. Others may invent physical diseases to gain medical attention (Münchausen syndrome), and an unexplained temperature is one means of doing this, either by manipulating the temperature recording device or even injection of contaminated materials.



Investigations


A rational approach should be based on the relative frequency of different causes and their importance to the health of the patient. Every case requires a comprehensive history and careful and repeated physical examination. History should include a thorough systems review with particular care concerning travel, occupational history and hobbies, pets and animal contact, drug prescriptions and other drug intake, familial diseases, previous illness and alcohol consumption.


A complete examination should include examination of the teeth, ears, fundoscopy and review of the skin in good light for faint rashes. This must be repeated at frequent intervals to spot important developing or fleeting physical signs. Temperature should be recorded methodically, although the great majority of patients never display the characteristic patterns of fever described in the textbooks.


Investigation may include samples sent for laboratory testing; non-invasive tests such as diagnostic radiology and ultrasound and radionuclide scanning; a tuberculin skin test or the more tuberculosis-specific interferon test on patients’ monocytes; and invasive testing such as biopsy, endoscopy and surgical exploration. A possible minimum set of investigations is listed in Fig. 3.35.1. Further investigation will depend upon what has already been done, and clues that may be obtained from the history and examination, working through all the possible differential diagnoses.


image

Fig. 3.35.1 Investigations for pyrexia of unknown origin. Red boxes are essential, purple the second set and yellow the third-stage investigations.

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Related posts:

Epidemiology of infectious diseases Infections of the immunocompromised host Pathogenesis of infectious disease Zoonoses Antibacterial therapy: principles Innate host defences to infectious disease

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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Pyrexia of unknown origin

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