An 'eruptive' variant of juvenile xanthogranuloma associated with langerhans cell histiocytosis.

The development of juvenile xanthogranuloma (JXG) as a sequel to langerhans cell histiocytosis (LCH) treated with chemotherapy is rare and the hypothesis is intriguing. This is a case of a 19-year-old woman who presented with progressive development of tan-red papules on the axilla and eyelids over a 1.5-year time span. A biopsy of an axillary lesion showed a prominent dermal infiltrate of foamy histiocytoid cells with occasional Touton-type multinucleate giant cells, consistent with JXG. Three years later, the patient presented with additional similar papules on the axilla and vulva as well as a painful mass in the pelvic bone and diabetes insipidus with an associated pituitary mass. An iliac crest bone biopsy showed an eosinophil-rich infiltrate admixed with histiocytoid cells with reniform nuclei, which expressed S100 and CD1a, consistent with a diagnosis of LCH. Nonetheless, an additional axillary papule was once again consistent with JXG, with negative reaction for S100 and CD1a with no Birbeck granules by electron microscopy. This case is unique by the co-existing presentation of multiple cutaneous JXG lesions and internally confined LCH lesions without an apparently associated chemotherapy, corroborating the concept that JXG and LCH may share a common histogenesis.