Patients commonly develop transient febrile illnesses, often caused by viruses, which subside spontaneously and a definitive diagnosis is never made. Other fevers persist but a diagnosis is reached rapidly and treatment started. In a few patients fever persists and defies diagnosis.
The best definition of pyrexia or fever of unknown origin (PUO or FUO) was given by Petersdorf and Beeson in the United States in 1951 in a paper describing the results of a study which they carried out in 100 patients. They defined PUO as a temperature of 38.3°C or above persisting or recurring during a period of 3 weeks which included 7 days' investigation in hospital. Principal causes of PUO are illustrated in the first information box.
Petersdorf and Beeson found that only one-third of their patients eventually proved to have an infection (the most common being tuberculosis). Another third had malignant disease (the most common being a reticulosis), and onefifth diseases of connective tissue. The remainder had various less common disorders including factitious fever. This is a condition (factitious pyrexia) where an individual, who often has medical or nursing training, mimics pyrexia-for example, by placing the thermometer on a radiator; there is usually an underlying psychiatric disorder in these cases. The second information box illustrates the investigation of PUO. Repeated examination for the development of new signs is most important.
| PRINCIPAL CAUSES OF PYREXIA OF UNKNOWN ORIGIN |
|---|
| Malignant disease |
|
| Diseases of connective tissue |
|
| Infections |
|
| Other causes |
|
| INVESTIGATION OF PYREXIA OF UNKNOWN ORIGIN |
|---|
| Retake the history |
|
| Repeat the examination |
|
| Review results of investigations (and repeat if indicated) |
|
| Consider further investigations |
|
| Consider therapeutic trial (generally as a last resort) |
|