Classic fever of unknown origin: analysis of a cohort of 87 patients according to the definition with qualitative study criterion

Objectives: The aim of this study was to evaluate the characteristics of fever of unknown origin (FUO) according to the definition with qualitative study criterion and of patients without diagnosis.

Materials and methods: Prospective observational study performed from 2009 to 2017 of all patients who were diagnosed with FUO according to the extended definition with qualitative study criterion. Demographic, clinical, diagnostic and evolving variables were evaluated.

Results: Of the 87 patients registered, 17.3% presented criteria of inflammation of unknown origin (IUO). The diagnoses were: non-infectious inflammatory diseases (NIID) in 19 patients (21.8%), infections in 15 (17.2%), miscellaneous in 14 (16.1%), malignant diseases in 13 (15%) and without diagnosis in 26 (29.9%). In 17.6% of the cases, a potentially diagnostic clue (PDC) was identified. The patients without diagnosis were characterized by a lower number of total PDC (5.9±3.3 vs. 8.7±3.4; P=.000), fewer clinical signs (.4±.6 vs. .9±.8; P=.001), a smaller number of tests in the previous study (2.7±2.1 vs. 4.6±2; P=.000), a shorter diagnostic interval (14.6±7.7 days vs. 21.4±9.5 days; P=.029) and less alteration of erythrocyte sedimentation rate (52.3±41.3mm/h vs. 89.8±42.7mm/h; P=.000), haemoglobin (12.9±1.7g/dl vs. 11.7±1.6g/dl; P=.003) and albumin (36.9±6.4g/l vs. 33.2±7.2g/l; P=.025). ¹⁸F-fluorodeoxyglucose positron-emission tomography combined with computed tomography (¹⁸F-FDG-PET/TC) proved to be helpful in 37% of the cases. Mortality was 6.8%.

Conclusions: The definition of FUO with qualitative study criterion incorporates a diagnostic protocol that provides clear benefits in terms of cost-effectiveness.