10269-RC-6 A Challenging Diagnosis of Erdheim-Chester Disease with Central Nervous System Involvement: A Case Report

Abstract Background Erdheim-Chester disease (ECD) is an extremely rare disease of non-Langerhans cell histiocytosis, characterized by systemic infiltration of foamy histiocytes. This disease commonly presents with skeletal lesions and frequently involves multiple organs. Central nervous system (CNS) invasion is recognized as a critical clinical manifestation of ECD, contributing to its complexity and diagnostic challenges. Case Presentation A male in his 40s presented in February 20XX with bilateral hydronephrosis caused by unexplained urinary tract strictures. Placement of a double-J stent and biopsy were performed; however, a definitive diagnosis could not be established. From March to April of the same year, the patient developed fatigue, arthralgia, and wheezing, ultimately requiring hospitalization after pneumonia. During the treatment, brain MRI revealed mass lesions in the ventral medulla, cavernous sinus and splenium of the corpus callosum. Worsening pneumonia led to intubation and tracheostomy, and the patient subsequently developed diabetes insipidus. After clinical stabilization, a stereotactic biopsy of the corpus callosum lesion in May, but a definitive diagnosis was not obtained. In July, the patient was transferred to our hospital for multidisciplinary treatment, and partial resection of the same lesion was performed. Histologically, there was infiltration of foamy histiocytes and Touton-type giant cells. Immunohistochemistry was positive for CD68 and CD163, negative for CD1a, and molecular analysis revealed the presence of the BRAF V600E mutation, leading to a diagnosis of ECD. Discussion ECD exhibits non-specific and highly diverse symptoms. CNS involvement frequently mimics other diseases, significantly complicating differential diagnosis and often resulting in delayed identification. Neurological symptoms may serve as an important diagnostic clue. Early and precise radiological, histopathological, and molecular assessments are critically important for diagnosing ECD. Recently, the BRAF V600E mutation has attracted attention as targeted molecular therapies such as BRAF inhibitors. Herein, we provide a literature-based discussion and report of this rare case.