E1520. Still Strange and Mysterious: Erdheim Chester Disease in the Molecular Era
  1. Xin Zhan; University of Iowa Hospitals and Clinics
  2. Aditi Patel; University of Iowa Hospitals and Clinics
  3. Yashant Aswani; University of Iowa Hospitals and Clinics
  4. Sarah Averill; University of Iowa Hospitals and Clinics
  5. Sedat Kandemirli; University of Iowa Hospitals and Clinics
  6. Leonardo Marcelino; University of Iowa Hospitals and Clinics
  7. Shehbaz Ansari; University of Iowa Hospitals and Clinics
Erdheim-Chester disease (ECD) is a rare, multisystemic, nonLangerhans cell histiocytic proliferative neoplastic disorder. There is a slight male preponderance and peak incidence occurs within the 5th-7th decades of life. Recent discovery of a strong association between the oncogenic BRAF mutation and the pathogenesis of ECD has led to ECD’s reclassification from an inflammatory disorder to a neoplastic process in 2016 – this has prompted a shift in the clinical workup for ECD to the use of new biologic treatments. The disease runs a smoldering course and can be fatal when untreated. Unlike its clinical cousin Langerhans cell histiocytosis, spontaneous regression is rare in ECD. Due to its rare and highly variable clinical presentation, radiology plays an important role in raising suspicion for ECD. We aim to describe the radiologic findings most often associated with ECD using a system-based approach, reference the changes in prognosis associated with its respective radiologic findings, and discuss the introduction of new biologic treatments in clinical practice.

Educational Goals / Teaching Points
Review ECD’s recent reclassification from an inflammatory disorder to a neoplastic process. Identify key radiologic features of ECD via a systematic approach. Understand how ECD prognosis is affiliated with certain image findings. Learn about the new clinical treatments for ECD as a neoplastic process.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Skeletal involvement is the most reliable feature of ECD, presenting in nearly 96% of cases, predominantly in the lower extremities. Retroperitoneal involvement is the most common extra-osseous site, afflicting up to 68% of patients. There is high variability in the cardiovascular manifestation of ECD, but nearly 75% of cases will present with some affiliation. Similarly, almost half of patients with ECD will have some form of pulmonary involvement. The head and neck are affected in nearly 1/3 of patients with ECD and extra-axial soft tissue and intra-parenchymal lesions. Rare sites of ECD include skin, breast, lymph nodes, thyroid, testis, and other visceral organs.

Prognosis of ECD is variable and largely dependent on the organ systems involved. The treatment for ECD varies according to disease severity. A new generation of oral molecular inhibitors of the MAP kinase pathway offers a new treatment option for patients with high-risk disease. Due to the novel nature of these treatments, long-term toxicities, optimal doses, and combinations are still under investigation. As these trials continue, radiologic evaluation of disease progression will continue to play an important role in the treatment of ECD.