Erdheim-Chester disease (ECD) is a rare multisystemic disorder, classified as non-Langerhans histiocytosis according to WHO-2016. It is a malignant neoplasm derived from myeloid progenitor cells, particularly from monocytic/dendritic origin. Its actual incidence is unknown, and fewer than a thousand cases have been reported to date in the medical literature. Recurrent somatic mutations involving the BRAF gene (BRAF V600E) and other components of the MAPK signaling pathway play a central role in its oncogenesis. Although rare, cases in patients under 40 years-old are reported. Frequently the median age of ECD patients is around 50-60 years-old, with a predominance of males (3:1). The disease may have a polymorphic clinical presentation, usually involving bones, central nervous system (CNS), pituitary and peri-aortic or retroperitoneal fibrosis with ureteral stenosis. Several therapeutic options can be used to control the disease, including corticosteroids, radiotherapy, interferon-α, purine analogues (2Cda or DCF), mono/polychemotherapy, and targeted drugs such as vemurafenib and dabrafenib.

To report one case of atypical presentation of ECD, manifested as acute obstructive abdomen in a patient under 20 years-old.

An 18-year-old woman, with no previous comorbidities, sought medical service at the HC-FMUSP due to abdominal pain, abdominal distension, and stopping of the elimination of gases and feces. Abdominal ultrasound showed an extensive mass with a cystic/solid aspect in the pelvic region. Exploratory laparotomy revealed a large solid mass adhered to the wall of the small intestine and the lateral wall of the rectum. A 15-cm enterectomy, ileo-bowel anastomosis, protective distal colostomy and insertion of a double-J catheter into the urinary tract were performed. Histopathological examination revealed atypical cell proliferation with staining for CD68+, CD163+, Ki67+ (20-30%) on immunohistochemistry study. Molecular test in a sample fixed in formalin and embedded in paraffin (FFPE) revealed the presence of BRAF V600E mutation, confirming the diagnosis of ECD. She started therapy with cladribine (2-Cda) 5 mg/m2, I.V., D1-D5, 30/30 days, for six cycles. After the end of chemotherapy, 18-FDG-PETCT was performed, compatible with complete metabolic response. She is currently asymptomatic and with an excellent quality of life.

ECD is a rare disorder that can present with atypical extra-osseous symptoms. We describe here an unusual case of a patient outside the usual age range for this disease, with intra-abdominal manifestation and a case of bowel occlusion, requiring exploratory laparotomy and extensive surgical resection. As this is a classically relapsing disease, it is known that isolated surgical resection is often ineffective. Although it has a mutation that works as a target for specific therapeutic intervention (BRAF inhibitors), these drugs are unavailable in the context of the Brazilian Public Health System. Thus, our patient underwent conventional cytotoxic treatment, with manageable toxicity and excellent therapeutic response.