1. Introduction
Typical clinical features of hairy cell leukemia (HCL) are cytopenias related to bone marrow infiltration and splenomegaly. Skeletal localization is a rare but well-recognized complication, mostly identified by painful osteolytic lesions in the proximal portions of long bones, although bone presentations with exclusive bone pain and few clinical and biological symptoms at presentation have been reported (1). Unusual presentation may pose a significant diagnosis challenge in routine practice. Only a few cases of HCL patients who have had a18F-FDG PET/CT have been published but all of them showed hypermetabolic localizations (1). Here, we report two cases of patients treated at the same medical center eight years apart from each other, with singular presentation of HCL characterized by threatening bone damage and lack or moderate bone marrow infiltration, and for whom18F-FDG PET/CT had an important role. The therapeutic options combining cladribine (CDA) and rituximab (R) were very effective, allowing durable complete remission (CR).