Background: A casual diagnosis cannot be established in 10% to 25% of the patients who are studied for fever of unknown origin (FUO). The long-term clinical outcome of these patients cannot be inferred from the literature. This study describes the results of a 5-year follow-up of 61 patients studied for FUO and discharged from the hospital with no causal diagnosis being established.
Methods: Patients meeting the classic criteria for FUO who were studied in the 1980s and discharged from the hospital without a casual diagnosis were followed up for at least 5 years or until death. Follow-up was performed by review of the patients' medical records or by consulting the treating physician and occasionally the patients themselves. The final diagnosis, clinical course (resolution of the fever and required treatments), and morality rate were studied.
Results: Of a cohort of 199 patients with FUO, 61 individuals (30%) were discharged from the hospital without a final diagnosis being established. A definite diagnosis could be established in 12 cases, mostly (eight of 12) within 2 months after discharge. Thirty-one individuals became symptom free during hospitalization or shortly following discharge. Eighteen patients had persisting or recurring fever for several months or even years after discharge, but 10 of them were considered to be finally cured. Four patients were treated with corticosteroids and six patients required intermittent therapy with nonsteroidal anti-inflammatory agents. Six patients died, but the cause of death was considered to be related to the disease that caused FUO in only two cases.
Conclusion: No single disease, particularly not tuberculosis, was found to be a cause of undiagnosed FUO. Most cases resolved spontaneously, and corticosteroids were seldom required. Most symptomatic patients could be treated with nonsteroidal anti-inflammatory drugs. The mortality rate in patients with undiagnosed FUO who were followed up for 5 years or more was only 3.2%.