Isolated CNS relapse of blastic plasmacytoid dendritic cell neoplasm

A 32-year-old man presented with fever, generalized bone pain, and pancytopenia. Bone marrow was diagnostic of blastic plasmacytoid dendritic cell neoplasm (BPDCN). Treatment with hyper-CVAD was initiated, and he attained a complete remission. He declined lumbar punctures (LPs) during the course of initial treatment. Prior to transplant, a bone marrow biopsy showed no evidence of residual BPCDN. Positron emission tomography/computed tomography scan results were normal. During his visit, he reported temporal headaches bilaterally. His pain progressed over several days, prompting brain magnetic resonance imaging, which was normal. An LP revealed a white blood cell count of 3081/uL, 80% of which were blasts that showed irregular nuclear contours, dispersed nuclear chromatin, prominent nucleoli, and moderate amount of cytoplasm (panel A, ×100 objective, ×1000 total magnification). Flow cytometry showed a blast population expressing CD4, bright CD56 (panel B), and bright CD123 (panel C), constituting approximately 87% of analyzed cells. The patient was diagnosed with central nervous system (CNS) BPDCN and was started on twice-weekly intrathecal methotrexate.

This case highlights a relatively common feature of BPDCN (ie, CNS relapse), which has an incidence of 20% to 25% during the disease course. LPs with preventative intrathecal chemotherapy at the time of diagnosis and during the course of initial treatment (usually 8 doses) are essential to decrease the risk of CNS relapse and improve long-term outcomes.