18F-FDG PET/CT in fever and inflammation of unknown origin

This thesis describes the role and the interpretation of imaging results with hybrid 18F-FDG PET/CT in patients with non-localizing or non-specific signs and symptoms like fever, weight loss, malaise and prolonged increased inflammatory parameters, without a diagnosis after routine diagnostic evaluation. Patients with either fever or inflammation of unknown origin (FUO or IUO) are a diagnostic dilemma, as the aetiology may vary from a self-limiting condition to occult malignancy. An important feature of 18F-FDG is its non-specificity: 18F-FDG shows increased uptake not only in malignant cells, but also in cells involved in infectious and inflammatory processes. Furthermore 18F-FDG PET/CT imaging is able to reveal functional alterations that precede the morphological changes and the integration of anatomical and functional images allows improved interpretation of both abnormal 18F-FDG uptake and suspicious morphological findings.
The heterogeneity of FUO and IUO aetiologies and the abundance of diagnostic possibilities have blurred an unambiguous diagnostic strategy in FUO and IUO. 18F-FDG PET/CT, however, shows a high diagnostic yield despite the heterogeneity of underlying aetiologies of the syndromes. After exclusion of systemic (non-focal) diseases 18F-FDG PET/CT has a high negative predictive value and is helpful in identifying patients with benign self-limiting conditions. Notwithstanding the relatively high costs 18F-FDG PET/CT has the potential to become a cost-effective routine imaging technique indicating the direction for further diagnostic decisions and thereby avoiding unnecessary, invasive, and expensive diagnostic investigations.