18F-FDG PET/CT in Erdheim–Chester Disease: Imaging Findings and Potential BRAF Mutation Biomarker

The purpose of this study was to evaluate ¹⁸F-FDG PET/CT for the diagnosis, management, and treatment of Erdheim–Chester disease (ECD). Methods: Our institutional database (2007–2017) was retrospectively reviewed for patients with pathologically proven ECD. A chart review yielded demographics, clinical information, and 5 categories of clinical impact. Two radiologists in consensus interpreted the images. Imaging findings were correlated with clinical data. Results: Seventy-one ¹⁸F-FDG PET/CT examinations were performed for 32 patients. The average SUV_max of the most active disease site was 9.2 (SD, 6.1). The most common sites involved were the skeleton (90.6% of patients, including 47% with axial and pelvic skeletal involvement), kidneys (81.3%), and central nervous system (CNS) (46.9%). Twenty-six patients were tested for a proto-oncogene B-Raf ^V600E (BRAF) mutation (18 had the mutation and 8 did not). The presence of a BRAF mutation was associated with ¹⁸F-FDG–avid CNS disease (P = 0.0357), higher SUV_max (P = 0.0044), and greater mortality (P = 0.0215). The presence of CNS disease had 88% specificity and a 92% positive predictive value for predicting the presence of a BRAF mutation. PET/CT examination results influenced patient management in 48% of cases (34/71). Conclusion:¹⁸F-FDG PET/CT results may act as a biomarker for the presence of a BRAF mutation, aid in establishing a diagnosis, guide biopsies, and gauge the treatment response in ECD patients. Axial and pelvic skeletal involvement is greater than previously reported.