Fever of unknown origin (FUO): evaluation of 50 cases with 18F-FDG PET/CT.

1953 Learning Objectives 1. Clinical significance and current issues of FUO 2. 18F-FDG PET/CT protocol and technical considerations 3. Usefulness, limitations and pitfalls of 18F-FDG PET/CT, in comparison to conventional imaging modalities OBJECTIVES FUO identifies a fever greater than 38.3oC which lasts for more than three weeks with no known cause. Previously, abdominal ultrasound (US), thoracoabdominal CT, and 67Ga scintigraphy have been mainly used as imaging methods for detecting the origin. However, no diagnosis is reached in up to 50% of cases. Recently the utility of 18F-FDG PET/CT to uncover the origin of FUO has been reported; the sensitivity and specificity of 18F-FDG PET/CT were quite high. We will present illustrative cases correlated with relevant clinical information and multimodality images. METHODS We reviewed 50 consecutive 18F-FDG PET/CT cases of patients with FUO from March 2005 to December 2014 obtained at our institution. RESULTS Thirty-six cases showed abnormal accumulation of 18F-FDG. Sensitivity, specificity, PPV, NPV of 18F-FDG PET/CT were 85%, 73%, 92%, and 57%, respectively. Concretely, patients with aortitis syndrome, iliopsoas muscle infection, systemic juvenile idiopathic arthritis (sJIA), Adult-onset Still’s disease were led to the final diagnosis by PET/CT imaging. On the other hand, we could not diagnose glomerulonephritis and temporal arteritis. CONCLUSION The reported overall mortality of FUO is 12-35%, and the causes are diverse; the spectrum of FUO etiology may include more than 200 diseases. More than 50% can’t be diagnosed by conventional imaging modalities. In such a situation, 18F-FDG PET/CT shows relatively high sensitivity and specificity, contributing to improved diagnosability. Although it has drawbacks such as high cost and limited availability, we believe 18F-FDG PET/CT should be used as a last resort for patients with indeterminate diagnoses.