One of the most difficult challenges in clinical medicine is arriving at a specific diagnosis for a fever of unknown origin (FUO). The cause of a FUO will frequently remain obscure and frustrate the best diagnostic efforts of an aggressive house staff backed up by learned consultants and a medical center equipped with the latest and most sophisticated diagnostic facilities.
The FUOs can be divided into four groups on the basis of their underlying cause: (1) infections, (2) neoplasms, (3) collagen-vasculitis disorders, and (4) miscellaneous (eg, sarcoid). In the most difficult and obscure cases, the clinician may not be able to assign the cause of a FUO to one of these groups and may be reluctant to initiate a trial of corticosteroid therapy for what is believed to be a vasculitis, in case an infection such as tuberculosis is the real villain. Thus, patients with FUO are subjected to a