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Introduction
Fever is a common pediatrie complaint that leads families to seek medical attention. Its routine management is the bread and butter of pediatrie practice. When fever is seen as prolonged beyond the expected time course (e.g., 10 days for a presumed viral respiratory tract infection or three weeks for mononucleosis), concern for fever of unknown origin (FUO) may ensue. This diagnosis is among the most challenging of diagnoses for health care providers.
Definition of Fever and FUO
The definition of "fever" varies among sources. Pragmatically, many define fever as a documented temperature above 38.O0C (100.40F).
Similarly, the definition of FUO varies. In series of pediatrie FUO, the definitions vary even more widely. A reasonable definition of FUO in children is "an illness accompanied by a temperature of 38.40C (101.10F) or higher at least once daily on at least 10 of the previous 14 days during which detailed history, physical examination, and laboratory screening tests do not identify a specific cause.
Most children referred for subspecialty evaluation with the diagnosis of FUO will not fulfill reasonable criteria for true FUO. Many will simply have fever without localizing signs and too-short duration of illness to consider FUO. Of those with more protracted fevers, most will have pseudo-FUO, some will have deconditioning, and a few will have true FUO.
Pseudo-FUO
Pseudo-FUO typically occurs when a child develops a series of benign, self-limited illnesses over a short period of time. Often this begins with a well-remembered acute illness with higher fever than is usual (and, occasionally, a febrile seizure). The fever abates over an expected period of time, but vague persistent symptoms, perceived low-grade fevers, and concern that the child fails completely to recover remain.
There often ensues another (clearly unrelated when thoughtfully reviewed) new febrile illness that is believed to be a continuation of the initial infection. This may occur several times, giving rise to a history that the child has had "continuous illness with fevers" for weeks to months.
Exacerbating this misperception is a variety of factors, including absence of similar illness in siblings or classmates, association with significant constitutional symptoms (weight loss, extreme fatigue, and/or reduced activity) at the time of the first illness, inability to attend school or function at a previous level associated...