Fever of unknown origin

Fever of unknown origin
Classification and external resources
ICD-10	R50
ICD-9-CM	780.6
MedlinePlus	003090
MeSH	D005335
[]

Fever of unknown origin (FUO), pyrexia of unknown origin (PUO) or febris e causa ignota (febris E.C.I.) refers to a condition in which the patient has an elevated temperature (fever) but despite investigations by a physician no explanation has been found.

If the cause is found it is usually a diagnosis of exclusion, that is, by eliminating all possibilities until only one explanation remains, and taking this as the correct one.

In 1961 Petersdorf and Beeson suggested the following criteria:

A new definition which includes the outpatient setting (which reflects current medical practice) is broader, stipulating:

Presently FUO cases are codified in four subclasses.

This refers to the original classification by Petersdorf and Beeson. Studies show there are five categories of conditions:

Nosocomial FUO refers to pyrexia in patients that have been admitted to hospital for at least 24 hours. This is commonly related to hospital-associated factors such as surgery, use of a urinary catheter, intravascular devices (i.e. "drip", pulmonary artery catheter), drugs (antibiotic-induced Clostridium difficile colitis, drug fever), and/or immobilization (decubitus ulcers). Sinusitis in the intensive care unit is associated with nasogastric and orotracheal tubes. Other conditions that should be considered are deep-vein thrombophlebitis, pulmonary embolism, transfusion reactions, acalculous cholecystitis, thyroiditis, alcohol/drug withdrawal, adrenal insufficiency, and pancreatitis.

Immunodeficiency can be seen in patients receiving chemotherapy or in hematologic malignancies. Fever is concomitant with neutropenia (neutrophil <500/uL) or impaired cell-mediated immunity. The lack of immune response masks a potentially dangerous course. Infection is the most common cause.

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