Fever of unknown origin (FUO) in immunocompetent and non neutropenic patien
ts is defined os recurrent fever of 38,3 degrees C or greater, lasting 2-3
weeks or longer, and undiagnosed after 1 week of appropriate evaluation. Th
e underlying diseases of FUO are numerous and infection accounts for only 2
0-40% of them. The majority of FUO-potients have autoimmunity and collagen
vascular disease and neoplasm, which are responsible for about 50-60% of al
l cases. In this respect FOU in its classical definition is clearly separat
ed from postoperative and neutropenic fever where inflammation and infectio
n are more common. Although methods that use in-vitro or in-vivo labeled wh
ite blood cells (WBCs) have a high diagnostic accuracy in the detection and
exclusion of granulocytic pathology, they are only of limited value in FUO
-patients in establishing the final diagnosis due to the low prevalence of
purulent processes in this collective. WBCs ore more suited in evaluation o
f the focus in occult sepsis. Ga-67 citrate is the only commercially availa
ble gamma emitter which images acute, chronic, granulomatous and autoimmune
inflammation and also various malignant diseases. Therefore Ga-67 citrate
is currently considered to be the tracer of choice in the diagnostic work-u
p of FUO. The number of Go-67-scans contributing to the final diagnosis was
found to be higher outside Germany than it has been reported for labeled W
BCs. F-18-2 ' -deoxy-2-fluoro-D-glucose (FDG) has been used extensively for
tumor imaging with PET. Inflammatory processes accumulate the tracer by si
milar mechanisms. First results of FDG imaging demonstrated, that FDG may b
e superior to other nuclear medicine imaging modalities which may be explai
ned by the preferable tracer kinetics of the small F-18-FDG molecule and by
a better spatial resolution of coincidence imaging in comparison to a conv
entional gamma camera.