#00064588

A 57-year-old female with a seven-year history of IgG kappa multiple myeloma, refractory to numerous treatments (carfilzomib, lenalidomide, dexamethasone, melphalan with autologous stem cell transplant, lenalidomide maintenance, and salvage daratumumab, pomalidomide and dexamethasone) undergoes a bone marrow biopsy for concern for relapse.  Peripheral blood reveals normocytic anemia and thrombocytopenia (hemoglobin 11.4 g/dL, MCV 88.5 fL, platelets 105K/μL); serum protein electrophoresis and immunofixation identify an IgG kappa monoclonal protein (0.81 g/dL).  The bone marrow biopsy confirms diffuse involvement by the plasma cell neoplasm (70% by CD138 immunostaining).  Within the aspirated bone marrow, rare megakaryocytes were observed containing granulocytes (100x objective, total magnification x1000), an incidental finding known as emperipolesis.

Megakaryocytic emperipolesis is a process in which hematopoietic cells migrate through the megakaryocytic canalicular system to gain access to circulation.  The travelling cells are encased within a vacuole (an emperisome), released into the host cytoplasm, fuse with the demarcation membrane system and exchange membrane with the host megakaryocyte, enhancing thrombocytogenesis.  After 10-40 minutes, the cells leave intact.  This cell-to-cell interaction must be kept in mind as a mimic when evaluating hemophagocytosis.  Also, increased emperipolesis can be seen in blood loss, reactive thrombocytosis, immune thrombocytopenia, gray platelet syndrome, myeloproliferative neoplasms and myelodysplastic neoplasms.