Secondary Plasma Cell Leukemia in a Recurrent Multiple Myeloma: Rare Case Scenario

Plasma cell leukemia (PCL) is an aggressive hematological condition characterized by the presence of plasma cells in the peripheral smear. It presents as de novo or may arise from multiple myeloma (MM), and hence is diagnosed as primary or secondary PCL, respectively. We report a case of 79-year-old patient diagnosed with MM two years prior to the admission to our institution with prior treatment with bortezomib, lenalidomide and dexamethasone (VRD) and daratumumab, pomalidomide and dexamethasone. Morphologic examination and flow cytometry studies performed on the peripheral smear demonstrated 45%-55% small to medium atypical plasma cells showing a kappa restriction and dim CD138 expression on flow cytometry analysis. The patient was started on brentuximab vedotin, etoposide, cytoxan and dexamethasone, which resulted in near complete elimination of the atypical plasma cells from the peripheral smear one week after the completion of two cycles. He received three cycles of brentuximab vedotin with a gradual decrease in serum free light chain. However, he eventually developed lethargy, weakness and seizures. The involvement of the central nervous system (CNS) by MM was confirmed with MRI, flow cytometry and cytology of cerebrospinal fluid. The treatment with whole brain radiation and ibrutinib was initiated. Our case report highlights the rare case of aggressive clinical course of MM leading to the development of plasmacytoma of kidney, secondary PCL and eventually spreading to the CNS.