Nuclear Medicine Imaging of FUO

Abstract

Fever of Unknown Origin (FUO) was initially defined as an illness of more than 3 weeks' duration, fever greater than 38.3°C (101°F) on several occasions, and diagnosis uncertain after 1 week of observation in the hospital [1]. This definition has subsequently been modified with an emphasis on ambulatory and outpatient investigation, and divided into four categories: classic (fever that is higher than 38.3°C on several occasions of at least 3 weeks' duration and an uncertain diagnosis after 3 days of hospitalization, three outpatient visits, or 1 week of ‘intelligent and invasive’ ambulatory investigation [2, 3]), nosocomial, immune deficient (neutropenic), and HIV-related [2, 4]. The most common causes of FUO can be grouped into three broad categories: infections (21–54%), malignancies (6–31%) and non-infectious inflammatory diseases (13–24%) [5–7]. The most important steps in the diagnostic work-up of FUO are a complete and repeated history taking, physical examination, and investigations in the search for potential diagnostic clues (PDCs) [8]. According to a recent review, non-invasive methods diagnose about 69.2% of the cases with FUO, whereas invasive methods perform better in 30.8% of the cases [9].