Erdheim Chester disease-An unusual presentation of a rare histiocytic disease in a 3-year old boy

Erdheim Chester disease (ECD) is a rare, multisystem non-Langerhans histiocytosis seen in adults characterized by a clinical triad of bone pains, bilateral painless exophthalmos and diabetes insipidus. Only 10 pediatric ECD cases are reported. We report here the youngest child in the literature, diagnosed at three years of age. He presented with osteolytic lesions in the skull, diabetes insipidus and bilateral proptosis. He was initially misdiagnosed and treated as Langerhan cell histiocytosis(LCH). In ECD, the typical radiological findings are symmetrical osteosclerosis of long bones. Osteolytic lesions are rare and if present are usually seen in the limbs. This is the first pediatric case with osteolytic lesions solely in the skull. A repeat biopsy confirmed ECD with the presence of foamy histiocytes in fibrous background positive for CD68 andCD163 and negative for CD1a and S100, typical histopathological features of ECD. The BRAFgene mutation was also detected. The patient responded well to interferon alpha therapy, which is now considered the first line treatment in ECD.