FDG PET/CT Findings of Erdheim-Chester Disease: Radiologic Response to a Novel Treatment Regimen.

Erdheim-Chester disease (ECD) is a rare form of non-Langerhans histiocytosis with deposition of lipid-laden macrophages in numerous organs. A 74-year-old man with a history of coronary artery disease, hypertension, and hyperlipidemia presented with nonspecific symptoms including back pain, nausea, vomiting, vertigo, and left leg pain. A neutrophil-predominant elevated WBC count and a bone biopsy revealing histiocytic proliferation positive for CD68 and CD163 and negative for S100 was noted. FDG PET/CT, MRA, and CTA images were obtained. We review the radiologic hallmarks of ECD and demonstrate the radiologic manifestations of response to combined BRAF and MEK inhibitor treatment.