False-Positive PET/CT for Lymphoma Recurrence Secondary to Langerhans Cell Histiocytosis

A case of Langerhans' cell histiocytosis following Hodgkin's disease

Langerhans' cell histiocytosis (LCH) is a group of disorders in various tissues characterized by the proliferation of Langerhans cells. It is rarely observed in adults. Langerhans cells are dendritic cells that express cluster of differentiation 1a (CD1a) and S100 protein, and contain Birbeck granules. Its etiopathogenesis remains to be elucidated. One possible etiological cause is a reactive proliferation of Langerhans cells following chemotherapy or radiotherapy for Hodgkin's disease (HD). A number of cases of LCH associated with malignant lymphoma have been reported previously. It may follow after the malignant lymphoma, or occur with it. However, fewer cases have been reported where the LCH followed after HD. In the present case report, a patient was diagnosed with HD following chemotherapy for LCH. As LCH was diagnosed, the patient was treated with a combination of various chemotherapeutic agents in two cycles of cyclophosphamide, vincristine, and prednisolone (COP), and eight cycles of cyclophosphamide, doxorubicin, vincristine, and prednisolone (CHOP). The patient went into a successful clinical remission. One year later, computed tomographic (CT) scans of the thorax and abdomen revealed augmentation of the tumor mass in the mediastinum. An excisional biopsy of the right inguinal lymph node was performed. The patient was diagnosed with nodular sclerosing Hodgkin's disease. Following four cycles of doxorubicin (Adriamycin), bleomycin, vinblastine and dacarbazine (ABVD) chemotherapy, a whole-body positron emission tomographic CT scan revealed a decrease in tumor mass in the mediastinum. At present, the patient remains in treatment, and the prognosis has yet to be fully determined.