FEVER of unknown origin (FUO) is a febrile illness (38.50C or more on multiple occasions) that has been present for more than 10 days with no apparent diagnosis after routine investigation.
FUO is classified into: classic FUO, nosocomial (hospital acquired) FUO, neutropenic (decrease of polymorphonuclear leucocytes in the blood) FUO and HIV associated FUO. The following presentation is limited to classic FUO in children.
There are about 100 diseases documented as a cause of FUO in children. In the Philippines, the data taken from the Textbook of Pediatrics and Child Health by Del Mundo, F., Estrada, F., Santos Ocampo, P., and Navarro, X., 4th edition showed that majority of cases of FUO are caused by infections 54.69 percent, malignant diseases 16.65 percent, collagen-vascular 7.69 percent, endocrine 7.69 percent and listed 13.44 percent as undiagnosed cases of FUO.
In children the predominant cause of fever of unknown origin (FUO) is infection. This pattern differs from the FUO in adults where the cause seems to have shifted to cancer as becoming more common. This shift away from infection in adults is partly attributed to early diagnosis by imaging modalities such as CT-scan and ultrasonographic studies that were not readily available in the past.
The infections that cause FUO in children vary from country to country. In the United States, viral syndrome is the predominant infection. In Saudi Arabia brucellosis is common. There is an emergence of cat-scratch disease as a cause of prolonged fever in Japan. And, in the Philippines, typhoid fever and tuberculosis are common infections causing FUO.
The future outcome in a child with FUO is much better than that reported for adults.
During the first week, acute infection (viral, bacterial and parasitic) is the most common cause of fever in children. Patients with viral infections are seldom febrile beyond 10 days. Bacterial infections treated with appropriate antibiotics will become afebrile in 2-3days. However, bacterial infections not properly treated will last for weeks to several months.
In the second week, majority of the cases of FUO are caused by chronic infections such as typhoid fever, tuberculosis, etc. or by encapsulated bacterial infections such as intra-abdominal abscess, pelvic abscess, brain abscess, etc.
During the third week, if the child is still febrile with no apparent cause, one must consider the possibility of collagen (connective tissue diseases such as juvenile rheumatoid arthritis, lupus erythematosus, etc); malignant disease (cancer), the most common are leukemia and lymphomas; and other causes such as factitious fever and drug fever.
Factitious fever is elevated body temperature produced artificially either deliberately or by accident. The parent or patient may manipulate the thermometer like placing the thermometer under hot water bag to elevate the temperature reading.
Prescription drugs, over-the-counter medications including cream, ointments and eye drops (atropine) can cause fever. Drug fever should be suspected in children receiving drugs known to produce febrile reactions 7-10 days after the institution of treatment. Fever usually remains at a constant level and not associated with other symptoms. Removal of offending drug is often associated with resolution of fever within three days. Fever persisting one week after the drug was withdrawn makes the diagnosis of drug fever unlikely.
In the hospital after the appropriate evaluation is completed, most of the serious and treatable disease will have been diagnosed and properly treated. Some will remain undiagnosed and continue to have fever. For those who appear healthy may be discharged from the hospital but must be carefully followed up until the resolution of their fever.
For those children who continue to have fever and appear ill should stay in the hospital until either the cause is identified and treated or the fever subsides spontaneously.
In 10-25 percent of children with FUO, the source of fever remains unknown even after adequate investigation. Most of these children will eventually become fever free and go on with their lives as normal children. The remaining few of these children with FUO will continue to have fever for months, sometimes more than a year but are otherwise well. (PVI)
