Erdheim-Chester Disease

Erdheim-Chester disease (ECD) is a histiocytic myeloid neoplasm that has the capability of involving multiple organs, thereby mimicking a number of immune-mediated diseases. The majority of ECD cases are associated with mutations in MAP kinase pathways, particularly BRAF but also NRAS, KRAS, and MAP 2K1. Most ECD patients harbor the mutation known as BRAFV600E. Histiocytic infiltrates in ECD can occur in almost any organ system but most commonly affect the bone, skin, retroperitoneum, heart, orbits, and lungs. The arterial disease in ECD is characterized by a periadventitial histiocytic infiltrate. This can lead to distinctive radiologic findings, such as the “coated aorta”—periadventitial thickening of the entire thoracoabdominal aorta. Full-body imaging with positron emission tomography/computed tomography (PET/CT) from the vertex of the head to the toes is usually the most valuable imaging study in ECD. Vemurafenib, a kinase inhibitor of mutated forms of BRAF including BRAFV600E, is approved for the treatment of ECD.