Erdheim–Chester disease mimicking Wilms tumor in a child: a diagnostic challenge

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. We report a case of Erdheim–Chester disease in a child treated in Lviv, Ukraine. A male child who initially presented at two years of age with central diabetes insipidus and recurrent urinary tract infections. Over the following two years, the patient developed bilateral obstructive uropathy, retroperitoneal and paravertebral masses, and multifocal central nervous system and orbital involvement, raising concern for Wilms tumor. Recurrent urinary tract infections and progressive hydronephrosis necessitated multiple surgical interventions. Histopathological findings were initially non-specific. Due to clinicoradiologic–pathologic discordance, tissue-based molecular analysis was performed, which identified a pathogenic BRAF V600E mutation, confirming the diagnosis of Erdheim–Chester disease. Targeted therapy with the BRAF inhibitor dabrafenib was initiated, resulting in clinical and radiological stabilization. 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, as misdiagnosis may lead to inappropriate surgical or chemotherapeutic interventions, delay targeted treatment, and adversely affect prognosis.