Nuclear medicine imaging in fever of unknown origin

Patients presenting with undiagnosed fever generally fall into two broad gr oups: firstly, those with co-existing disease or recent surgery, and second ly those with pyrexia but who are otherwise more or less well. A pyogenic c ause for fever is significantly more Likely in the first group as compared with the second. Radionuclide agents which are currently freely available f or investigating undiagnosed fever are labelled leukocytes, Ga-67, and radi olabelled human immunoglobulin (HIG). Labelled leukocytes are generally pre ferable in the group with co-existing disease (occult infection), whereas G a-67 should be used in the second group, which can appropriately be called fever of unknown origin (FUO). The lower specificity of (67)G can be percei ved as an advantage in this context in view of the wide range of pathologie s capable of causing FUO. The role of HIG in undiagnosed fever is unsettled . In general, Ga-67 is more helpful than labelled leukocytes when the cause of an FUO is intrathoracic, although the reverse is likely to be true for intra-abdominal causes, partly because of physiological excretion of Ga-67 in the gut. Postoperative fever is an indication for a leukocyte scan. Pati ents with haematological malignancies occasionally present as an FUO, but p atients with chronic renal disease should be approached as occult infection . Investigating children with undiagnosed fever is a particularly difficult problem. For the future, we need agents which are particularly effective f or localising chronic inflammation and, of secondary importance, agents abl e to distinguish between infective and non-infective causes of inflammation .