18F‐fluorodeoxyglucose–positron emission tomography scanning is more useful in followup than in the initial assessment of patients with Erdheim‐Chester disease

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Abstract
Objective: Erdheim‐Chester disease (ECD) is a rare form of non–Langerhans' cell histiocytosis. The aim of this study was to assess the value of whole‐body scanning with 18F‐fluorodeoxyglucose–positron emission tomography (FDG‐PET) in a large cohort of ECD patients from a single center.Methods: We retrospectively reviewed all PET scans performed on 31 patients with ECD who were referred to our department between 2005 and 2008. PET images were reviewed by 2 independent nuclear medicine specialist physicians and were compared with other imaging modalities performed within 15 days of each PET scan.Results: Thirty‐one patients (10 women and 21 men; median age 59.5 years) underwent a total of 65 PET scans. Twenty‐three patients (74%) were untreated at the time of the initial PET scan, whereas 30 of the 34 followup PET scans (88%) were performed in patients who were undergoing immunomodulatory therapy. Comparison of the initial and followup PET scans with other imaging modalities revealed that the sensitivity of PET scanning varied greatly among the different organs studied (range 4.3–100%), while the specificity remained high (range 69.2–100%). Followup PET scans were particularly helpful in assessing central nervous system (CNS) involvement, since the PET scan was able to detect an early therapeutic response of CNS lesions, even before magnetic resonance imaging showed a decrease in their size. PET scanning was also very helpful in evaluating the cardiovascular system, which is a major prognostic factor in ECD, by assessing the heart and the entire vascular tree during a single session.Conclusion: The results of our large, single‐center, retrospective study suggest that the findings of a FDG‐PET scan may be interesting in the initial assessment of patients with ECD, but its greater contribution is in followup of these patients.