Erdheim-Chester Disease in Adults: 11 Cases from a Canadian Rare Diseases Program

Erdheim-Chester disease (ECD) is a rare histiocytic neoplasm with highly variable, multisystem manifestations that present significant diagnostic and therapeutic challenges. This retrospective multicenter case series included 11 adult patients diagnosed with biopsy-proven ECD across Canada between January 2015 and June 2024. The cohort comprised six females and five males with a median age of 55 years (range 41-74). PET-CT was used for disease staging and treatment monitoring in nine cases. The most commonly involved sites were bone (n=8), kidney (n=6), and lungs (n=5). BRAF V600E mutations were detected in seven patients. Treatments included vemurafenib, interferon, tocilizumab, cladribine, cobimetinib, and cytarabine. Treatment responses varied, with several patients achieving remission or stable disease, while others had progressive or end-stage disease. This study highlights the clinical heterogeneity of ECD and the value of integrating histopathology, molecular profiling, and imaging to guide management and improve outcomes.