C. Langerhans cell histiocytosis
Histopathological examination revealed a dense infiltration of lower epidermis and upper dermis by atypical Langerhans cells. These cells were large and had a characteristic coffee bean–shaped grooved vesicular nuclei and moderate amphophilic cytoplasm. They also stained positive for CD1a and Langerin on immunohistochemistry. Results of routine blood investigations were normal, along with negative results for HLA-B51 and enzyme-linked immunosorbent assay for Epstein-Barr virus IgM and IgG. Positron emission tomography showed fluorodeoxyglucose-avid involvement of bone marrow, skeletal system (in the form of lytic lesions), lungs, bilateral salivary glands, mucosae, and skin of flexural areas and scalp. Pituitary involvement in the form of diabetes insipidus was confirmed on contrast-enhanced magnetic resonance imaging of sella, which revealed absence of posterior pituitary bright spot. Thus, a final diagnosis of multisystem Langerhans cell histiocytosis (LCH) with organ dysfunction of low-risk type was made.