Erdheim–Chester Disease Mimicking Wilms Tumor in a Child: A Diagnostic Challenge

Background Erdheim–Chester disease (ECD) is a rare non-Langerhans cell histiocytosis driven by activating mutations of the MAPK signaling pathway, most commonly BRAF V600E. Pediatric cases are exceedingly rare and often present with atypical, multisystem manifestations, resulting in significant diagnostic delay. Renal and retroperitoneal involvement may mimic primary renal malignancies, particularly Wilms tumor. Case presentation We report a case of Erdheim–Chester disease in Ukraine, Lviv. A male child who initially presented at the age of two years with central diabetes insipidus and progressive urinary tract infections. Over two years, the patient developed bilateral obstructive uropathy, retroperitoneal and paravertebral masses, and multifocal central nervous system and orbital involvement. Recurrent urinary tract infections and progressive hydronephrosis necessitated multiple surgical interventions. Initial histopathological findings were inconclusive and suggested alternative diagnoses, including ganglioneuroma and reactive histiocytic proliferation. Due to discordance between clinical, radiological, and histological findings, extended immunohistochemical and molecular analyses were performed. Detection of a pathogenic BRAF V600E mutation confirmed the diagnosis of Erdheim–Chester disease. Lifelong targeted therapy with the BRAF inhibitor dabrafenib was initiated, resulting in clinical stabilization. Conclusions This case highlights the diagnostic complexity of Erdheim–Chester disease in children and emphasizes the importance of considering histiocytic disorders in the differential diagnosis of renal and retroperitoneal masses. Multisystem involvement, atypical imaging findings, and molecular testing are key elements for accurate diagnosis and appropriate management, particularly in cases mimicking Wilms tumor.