Ilse J.E. Kouijzer

FDG-PET in Fever of Unknown Origin

Fever of unknown origin (FUO) is commonly defined as fever higher than 38.3°C on several occasions during at least 3 weeks with uncertain diagnosis after a number of obligatory tests. FUO remains a clinical challenge as no diagnosis is reached in up to 50% of cases. In general, infection accounts for one-fourth of cases of FUO, followed by neoplasm and noninfectious inflammatory diseases. FDG-PET is a sensitive diagnostic technique for the evaluation of FUO. Especially integrated imaging combining PET and CT facilitates anatomical localization of focally increased FDG uptake, thereby guiding further diagnostic tests to achieve a final diagnosis. FDG-PET/CT appears to be a more sensitive diagnostic tool in FUO than stand-alone FDG-PET, because of the precise anatomical localization of small lesions and better differentiation between physiological and pathologic metabolic foci. With FDG-PET/CT becoming widely available, FDG-PET/CT should be a routine procedure in the workup of FUO.

18F-FDG PET/CT optimizes treatment in staphylococcus aureus bacteremia and is associated with reduced mortality

Metastatic infection is an important complication of Staphylococcus aureus bacteremia (SAB). Early diagnosis of metastatic infection is crucial, because specific treatment is required. However, metastatic infection can be asymptomatic and difficult to detect. In this study, we investigated the role of 18F-FDG PET/CT in patients with SAB for detection of metastatic infection and its consequences for treatment and outcome. Methods: All patients with SAB at Radboud University Medical Center were included between January 2013 and April 2016. Clinical data and results of 18F-FDG PET/CT and other imaging techniques, including echocardiography, were collected. Primary outcomes were newly diagnosed metastatic infection by 18F-FDG PET/CT, subsequent treatment modifications, and patient outcome. Results: A total of 184 patients were included, and 18F-FDG PET/CT was performed in 105 patients, of whom 99 had a high-risk bacteremia. 18F-FDG PET/CT detected metastatic infectious foci in 73.7% of these high-risk patients. In 71.2% of patients with metastatic infection, no signs and symptoms suggesting metastatic complications were present before 18F-FDG PET/CT was performed. 18F-FDG PET/CT led to a total of 104 treatment modifications in 74 patients. Three-month mortality was higher in high-risk bacteremia patients without 18F-FDG PET/CT performed than in those in whom 18F-FDG PET/CT was performed (32.7% vs. 12.4%, P = 0.003). In multivariate analysis, 18F-FDG PET/CT was the only factor independently associated with reduced mortality (P = 0.005; odds ratio, 0.204; 95% confidence interval, 0.066–0.624). A higher comorbidity score was independently associated with increased mortality (P = 0.003; odds ratio, 1.254; 95% confidence interval, 1.078–1.457). Conclusion: 18F-FDG PET/CT is a valuable technique for early detection of metastatic infectious foci, often leading to treatment modification. Performing 18F-FDG PET/CT is associated with significantly reduced 3-mo mortality.

The value of 18F-FDG-PET/CT in diagnosis and during follow-up in 273 patients with chronic Q fever

In 1%–5% of all acute Q fever infections, chronic Q fever develops, mostly manifesting as endocarditis, infected aneurysms, or infected vascular prostheses. In this study, we investigated the diagnostic value of 18F-FDG PET/CT in chronic Q fever at diagnosis and during follow-up. Methods: All adult Dutch patients suspected of chronic Q fever who were diagnosed since 2007 were retrospectively included until March 2015, when at least one 18F-FDG PET/CT scan was obtained. Clinical data and results from 18F-FDG PET/CT at diagnosis and during follow-up were collected. 18F-FDG PET/CT scans were prospectively reevaluated by 3 nuclear medicine physicians using a structured scoring system. Results: In total, 273 patients with possible, probable, or proven chronic Q fever were included. Of all 18F-FDG PET/CT scans performed at diagnosis, 13.5% led to a change in diagnosis. Q fever–related mortality rate in patients with and without vascular infection based on 18F-FDG PET/CT was 23.8% and 2.1%, respectively (P = 0.001). When 18F-FDG PET/CT was added as a major criterion to the modified Duke criteria, 17 patients (1.9-fold increase) had definite endocarditis. At diagnosis, 19.6% of 18F-FDG PET/CT scans led to treatment modification. During follow-up, 57.3% of 18F-FDG PET/CT scans resulted in treatment modification. Conclusion: 18F-FDG PET/CT is a valuable technique in diagnosis of chronic Q fever and during follow-up, often leading to a change in diagnosis or treatment modification and providing important prognostic information on patient survival.

Fever of Unknown Origin: the Value of FDG-PET/CT

Fever of unknown origin (FUO) is commonly defined as fever higher than 38.3°C on several occasions during at least 3 weeks with uncertain diagnosis after a number of obligatory investigations. The differential diagnosis of FUO can be subdivided in four categories: infections, malignancies, noninfectious inflammatory diseases, and miscellaneous causes. In most cases of FUO, there is an uncommon presentation of a common disease. FDG-PET/CT is a sensitive diagnostic technique for the evaluation of FUO by facilitating anatomical localization of focally increased FDG uptake, thereby guiding further diagnostic tests to achieve a final diagnosis. FDG-PET/CT should become a routine procedure in the workup of FUO when diagnostic clues are absent. FDG-PET/CT appears to be a cost-effective routine imaging technique in FUO by avoiding unnecessary investigations and reducing the duration of hospitalization.

Clinical application of FDG-PET/CT in metastatic infections

FDG-PET/CT has proven its clinical value and cost-effectiveness in diagnosing metastatic infections in patients with Gram-positive bacteremia. In identification of metastatic foci, FDG-PET/CT is useful as a screening method when localizing symptoms are absent because it provides whole-body coverage. FDG-PET/CT detects early metabolic activity rather than the late anatomical changes as visualized by computed tomography and magnetic resonance imaging. FDG-PET/CT allows more precise localization of infection within a shorter time span between injection and diagnosis as compared to conventional nuclear imaging. This review focuses on the clinical application of imaging of metastatic infectious diseases, with an emphasis on FDG-PET/CT putting it in perspective with other imaging modalities.

18F-FDG PET/CT for the Detection of Septic Embolisms in Patients with Infectious Endocarditis

outcome (5). However, timely identification of septic embolisms is often difficult. Often these septic foci are not suspected in the absence of positive blood cultures or when blood cultures are obtained during antibiotic treatment. Furthermore, up to 50% of patients with septic embolisms do not have any localizing signs and symptoms (6,7). In the current study, more than half (60%) of the patients with an infectious complication were asymptomatic. 18 F-FDG PET/CT was the only initially positive imaging technique in 55.5% of true-positive cases (1). To date, a structural protocol for diagnosis of septic embolisms is lacking. Besides the study of Kestler et al., other investigators have shown evidence that 18 F-FDG PET/CT could be of diagnostic value in patients with septic embolisms. Several case reports have shown the value of 18 F-FDG PET/CT in the diagnosis of extracardiac foci in patients with infectious endocarditis (8). A small study of 24 patients with 25 episodes of infectious endocarditis investigated the value of 18F

18F-FDG PET/CT in Detecting Metastatic Infection in Children

Purpose of the Report Metastatic infection is a severe complication of bacteremia with high morbidity and mortality. The aim of this study was to investigate the diagnostic value of 18F-FDG PET combined with CT (FDG PET/CT) in children suspected of having metastatic infection. Methods The results of FDG PET/CT scans performed in children because of suspected metastatic infection from September 2003 to June 2013 were analyzed retrospectively. The results were compared with the final clinical diagnosis. Results FDG PET/CT was performed in 13 children with suspected metastatic infection. Of the total number of FDG PET/CT scans, 38% were clinically helpful. Positive predictive value of FDG PET/CT was 71%, and negative predictive value was 100%. Conclusions FDG PET/CT appears to be a valuable diagnostic technique in children with suspected metastatic infection. Prospective studies of FDG PET/CT as part of a structured diagnostic protocol are needed to assess the exact additional diagnostic value.