Adult onset langerhans cell histiocytosis limited to the skin

Langerhans cell histiocytosis (LCH) is a proliferative disease commonly seen in the pediatric population but rarely encountered in the adult population. The exact etiology remains unclear. It has various clinical features and is very likely to be misdiagnosed. Histopathology and immunohistochemistry are very important for the diagnosis of LCH. Treatment protocols remain controversial. Herein, we report a rare adult onset LCH, which is confined to the skin. A 50-year-old Chinese man presented with a nodule with itchy rashes on the left lower leg, which gradually grew in size for the last 6 months. He also had multiple scattered rashes on the right lower leg. The skin biopsy demonstrated Langerhans cells infiltrating the superficial dermis, and the tumor cells were positive for CD1a and S-100 expression. The diagnosis was LCH based on the histopathological and immunohistochemistry results.