Co-existence of Langerhans cell histiocytosis and reticulohistiocytosis with initial presentation of skull lesions: A case report.

Langerhans cell histiocytosis (LCH) is a rare histiocytic disorder resulting from dysregulated clonal proliferation of Langerhans cells. Reticulohistiocytosis (RH) is another rare histiocytosis caused by the proliferation of histiocytes other than Langerhans cells. Co-existence of LCH and RH in different organs and in the same skin area has not been reported. We present the case of a 20-year-old woman who initially had co-existing bone LCH and cutaneous RH. After 1 year of chemotherapy with cytarabine, bone LCH significantly improved but cutaneous LCH developed in the same area where cutaneous RH was, resulting in hybrid LCH and RH of the skin. This unique history provides some evidence to support the theory that LCH and RH originate from the same stem cells and subsequently develop into hybrid LCH and RH of the skin in a cytokine environment influenced by chemotherapy. Repeat skin biopsies may be considered for adjusting treatment regimens in LCH patients whenever pre-existing skin lesions progress.