A rare case of hairy cell leukaemia presenting as an isolated pathological neck of femur fracture

Hairy cell leukaemia (HCL) is a rare B non-Hodgkin lymphoma that commonly presents with cytopenias, splenomegaly and infection. We report 58-year-old man who presented acutely left hip pain. MRI scan identified pathological neck of femur fracture, along subacute sacral fracture. A total replacement was performed sent for histology which showed infiltration the bone surrounding tissue by monotonous small lymphocytes. Immunohistochemistry positive CD20, CD25 BRAF (VE1) negative CD5, CD10, cyclin D1 S100, consistent HCL. V600E mutation also using real-time PCR, supporting diagnosis. Full blood examination film normal at presentation. Bone marrow aspirate normal, no clonal cells on flow cytometry cytogenetics. FDG-PET did not show or lymphadenopathy, but insufficiency fracture PET-avid, possibly representing second distinct site involvement. Due to ongoing pain patient treated radiation sacrum remains well follow-up. In summary we present case HCL presenting as multiple localised skeletal lesions without any detectable organ involvement, highlighting unique presentation this condition.