18F-fluoride PET/CT aspect of an unusual case of Erdheim-Chester disease with histologic features of Langerhans cell histiocytosis.

We report the case of a 63-year-old woman with Erdheim-Chester disease (ECD) and histologic features of Langerhans cell histiocytosis, both extremely rare histiocytic proliferations responsible of skeletal and extraskeletal involvement. 18F-Fluoride PET/CT revealed multiple intense focal uptake scattered throughout the skeleton. We also performed an 18F-FDG PET/CT which point out visceral and vascular involvement. This case illustrates the interest of PET/CT in ECD, a rare polymorphus and systemic disease, and in our knowledge, this is the first reported illustration of 18F-fluoride PET/CT findings in this pathology.