Case Report: Erdheim-Chester disease presenting as abdominal cocoon syndrome.

Erdheim-Chester disease (ECD) is a rare histiocytic neoplasm driven by MAPK pathway mutations. Although it frequently involves the bones, heart, and kidneys, initial manifestations predominantly affecting the gastrointestinal tract and mesentery are exceedingly rare, often leading to significant delays in clinical diagnosis. This report describes a 61-year-old female patient who presented with recurrent abdominal pain over several months and was initially diagnosed with a conventional "adhesive bowel obstruction" at an external hospital. However, surgical exploration revealed a classic "abdominal cocoon" presentation and symptoms showed no significant improvement postoperatively. Abdominal CT upon admission revealed diffuse thickening of the peritoneum, omentum, and mesentery with substantial peritoneal and pelvic effusion. Laboratory findings revealed autoimmune serological abnormalities, including positive ANA, anti-SSA, and anti-Ro-52 antibodies, without characteristic clinical manifestations of a defined connective tissue disease. Pathological review of resected specimens revealed extensive foamy histiocytic proliferation in the small intestine and greater omentum, with immunohistochemical findings supporting ECD and molecular confirmation of the BRAFV600E mutation. Systemic PET-CT further delineated multisystem infiltration, and bone marrow evaluation ruled out the possibility of overlapping myeloid tumors. Following multidisciplinary team (MDT) confirmation, the patient received vemurafenib-based targeted therapy, together with hydroxychloroquine following rheumatologic evaluation for the associated immunological abnormalities, resulting in substantial clinical improvement. This case highlights a rare gastrointestinal manifestation of ECD mimicking a surgical disorder and underscores the importance of integrating imaging, pathology, and molecular testing in patients with atypical intestinal manifestations.