Selected Case From the Arkadi M. Rywlin International Pathology Slide Seminar: Involvement of Skin and Soft Tissue by Erdheim-Chester Disease.

Erdheim-Chester disease is a rare form of non-Langerhans cell histiocytosis that preferentially involves long bones but can affect a variety of other organs. Initial presentation with extraskeletal involvement is not unusual and is most commonly observed in the central nervous system, heart, retroperitoneum, lungs, and skin. Initial presentation of the disease as a subcutaneous soft tissue mass is exceedingly rare and may pose difficulties for diagnosis. We describe a case of Erdheim-Chester disease that initially presented as a cutaneous and subcutaneous soft tissue mass in the right posterior shoulder of a 52-year-old man.