Therapeutic trials
Use of therapeutic interventions to establish a diagnosis is discouraged. Many illnesses, including a variety of infections, respond transiently to corticosteroids, only to have the disease later progress in the face of corticosteroid-induced immune suppression (17). It has been stated that naproxen reduces fever related to malignancies but not that due to infections, and thus it might help differentiate between FUO due to tumor and that due to infection (18). However, this observation has not been verified. Certainly, if a patient's fever is shown to be caused by a malignancy, any one of several nonsteroidal anti-inflammatory drugs can reduce the fever and make the patient feel better, but response to these drugs should not be used to establish a diagnosis. Trials of antibiotic agents rarely are specific and serve only to obscure subsequent attempts to establish an etiologic agent.
If a patient with FUO is clinically stable and an extensive workup performed in consultation with an infectious diseases expert has failed to establish a cause, it is reasonable to carefully observe the patient rather than pursue further invasive diagnostic tests. The majority of patients in whom a diagnosis has not been established after an extensive workup ultimately experience resolution of the fever and have good outcomes (8,19). These patients need careful follow-up by both a specialist in infectious diseases and their primary care physician.
Conclusion
FUO can be an evasive clinical problem and its cause difficult to detect. Primary care physicians are often the first to encounter this condition and are essential in its discovery and follow-up. Because potential causes of FUO are many, physicians need to take a well-planned, strategic approach to the workup of a patient with this problem. Understanding the etiologic factors of FUO and incorporating thorough history taking and physical examination with more complex testing can lead to timely discovery of the source of a patient's FUO.
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