Plasmablastic Lymphoma Mimicking Osteomyelitis of Femur in an Immunocompetent Individual: A Case Report.

Plasmablastic lymphoma (PBL) is an aggressive type of diffuse large B-cell lymphoma. It is most commonly seen in patients with human immunodeficiency virus (HIV) infection and other immunodeficiencies manifesting commonly in the form of oral lesions. Here, we report a case of an HIV-negative, immunocompetent elderly male who presented with a painful solitary tender lesion on the right anterior lateral thigh. A preliminary diagnosis of osteomyelitis (right femur) from a possibly infected dynamic compression plate was made following initial ultrasound and MRI of the right lower extremity. An attempt was made to incise and drain the lesion, which was abruptly stopped as it resulted in drainage of copious blood, leading to hemodynamic instability. Histopathology of the specimen revealed findings consistent with PBL. The diagnosis of PBL was further confirmed by immunohistochemical staining, which was positive for CD138, MUMI, and CD56 and negative for CD20 and ALK. Due to its rarity and heterogeneous presentations, PBL could be easily overlooked clinically in immunocompetent patients. Therefore, our case highlights the importance of considering the diagnosis of PBL even in lesions whose course is consistent with other infectious bone pathologies.