Skeletal involvement in Erdheim-Chester disease: Multimodality imaging features and association with the BRAF^V600E mutation

Objective: The aim of this study was to characterize the distribution of skeletal involvement in Erdheim-Chester disease (ECD) by using radiography, computed tomography (CT), ¹⁸F-FDG positron emission tomography/computed tomography (PET/CT), and bone scans, as well as looking for associations with the BRAF^V600E mutation. Material and methods: Prospective study of 50 consecutive patients with biopsy-confirmed ECD who had radiographs, CT, ¹⁸F-FDG PET/CT, and Tc-99m MDP bone scans. At least two experienced radiologists with expertise in the relevant imaging studies analyzed the images. Summary statistics were expressed as the frequency with percentages for categorical data. Fisher's exact test, as well as odds ratios (OR) with 95 % confidence intervals (CI), were used to link imaging findings to BRAF^V600E mutation. The probability for co-occurrence of bone involvement at different locations was calculated and graphed as a heat map. Results: All 50 cases revealed skeletal involvement at different regions of the skeleton. The BRAF^V600E mutation, which was found in 24 patients, was correlated with femoral and tibial involvement on ¹⁸F-FDG PET/CT and bone scan. The appearance of changes on the femoral, tibial, fibular, and humeral involvement showed correlation with each other based on heat maps of skeletal involvement on CT. Conclusion: This study reports the distribution of skeletal involvement in a cohort of patients with ECD. CT is able to detect the majority of ECD skeletal involvement. Considering the complementary nature of information from different modalities, imaging of ECD skeletal involvement is optimized by using a multi-modality strategy.