The Case | Unexplained perirenal infiltration

This case report describes the diagnosis of Erdheim-Chester disease in a 69-year-old man who initially presented with hypertension and a bilateral mass around the kidneys, described as ‘hairy kidneys’. Despite the absence of typical histological features and common bone lesions, molecular analysis revealed a genetic mutation in the MAP2K1 gene, confirming the activation of the MAPK metabolic pathway. The process of differential diagnosis is outlined.