Abstract
Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis and multisystem disease. First described in 1930, there are no more than 750 cases reported. The etiology remains unknown, but a majority of cases of ECD and Langerhans cell histiocytosis were found to have clonal mutations involving genes of the mitogen-activated protein kinase pathway. We recently encountered a 53-year-old male patient with extensive ECD involving the systemic lymph nodes, pleura, liver, and long bones clinically mimicking malignant lymphoma. Biopsies were performed at multiple sites, including a pleural mass, an external iliac lymph node, bone marrow, and the liver. Based on histopathological and immunohistochemical findings of positivity for CD68 and negativity for CD1a and S-100, the patient was diagnosed with ECD. Interferon-α was administered as the first-line treatment, but the patient rapidly progressed to hepatic failure after 2 months of treatment. We report this rare case of ECD clinically mimicking malignant lymphoma and diagnosed by careful pathological review.