Unusual presentation of Erdheim-Chester disease in a child with acute lymphoblastic leukemia

Table 1 Summary of Erdheim-Chester disease

Age	Middle aged and elderly patients predominantly affected
Site	Any tissue or organ can be affected and clinical manifestations depend upon the organ of involvement. Bone is most frequently affected (> 90%), however, at least one soft tissue component is seen in more than 50% of patients
Pathophysiology	Shows polyclonal proliferation of histiocytes associated with abnormal Th1 immune response. The recent studies however have suggested a clonal origin by demonstrating BRAFV600E mutations in more than 50% cases
Diagnostic criteria (Radiologic)	Bilateral, symmetric cortical osteosclerosis of the diaphyseal and metaphyseal regions of the long bones
	Symmetric bilateral abnormally intense Tc labelling of the distal ends of the long bones
(Histopathologic)	Characteristic “coated aorta” or “hairy kidneys” on CT scan; Xanthogranulomatosis or polymorphic granuloma with foamy/lipid laden histiocytes with immunoreactivity to CD68, but negative for CD1a and Langerin
Treatment	IFN-α and pegylated IFN-α are preferred for the treatment
	Anakinra (recombinant IL1R antagonist) and infliximab (anti-TNF-α antibody) may be used for second-line treatment
	Vemurafenib (an inhibitor of BRAF) especially for the patients with severe and refractory BRAFV600E histiocytoses
Follow-up (with PET-CT)	Useful for assessing extent of involvement both skeletal and extraskeletal components, activity and progression of disease, and monitoring of therapy

PET-CT: Positron emission tomography-computed tomography; Tc: ^99mTechnetium; CT: Computed tomography; FDG: Fludeoxyglucose; IL: Interleukin; BRAFV600E: V-raf murine sarcoma viral oncogene homolog B1V600E; IFN: Interferon; TNF: Tumor necrosis factor; BRAF: V-raf murine sarcoma viral oncogene homolog B1.

Table 2 Differential diagnoses of Erdheim-Chester disease

Radiologic differential diagnoses
With osteosclerotic lesions	Renal osteodystrophy, Pagets disease, myelofibrosis, osteoblastic metastases, chronic osteomyelitis, metabolic bone disorders
With osteolytic lesions in children	Langerhans cell histiocytosis, infection, metastatic neuroblastoma
Histologic
Langerhans cell histiocytosis	Positive for S100, CD1a, and Langerin
Rosai-Dorfman disease	Histiocytes show emperipolesis; positive for S100 and CD68; negative for CD1a, and Langerin
Juvenile xanthogranuloma	Lack characteristic radiologic features of ECD; positive for factor XIIIa, CD68, CD163, fascin, and CD14, negative for CD1a, S100, and Langerin
Solitary/multicentric reticulohistiocytoma	Lack characteristic radiologic features of ECD; positive for factor XIIIa, CD68, CD163, fascin, and CD14; negative for CD1a, S100, and Langerin

ECD: Erdheim-Chester disease.