Plasma cells are uncommonly observed in the peripheral blood smear. They are normal lymph nodes, spleen, connective tissue, and bone marrow constituents. The presence of plasma cells in the peripheral blood indicates many conditions, mainly related to infections, immune disorders, malignancies, toxic exposures, hypersensitivity reactions, and their responses.
Although mature plasma cells have a distinct appearance, they still may be confused morphologically with immature plasma cells and other cells with inclusions, reactive changes, or nucleated red blood cells with altered identities. In the image to the right, a plasma cell is present. The plasma cell has an eccentric, immature nucleus, a prominent Golgi apparatus (para nuclear hof), and a muddy chromatin pattern. The clumping and stacking of the erythrocytes, typical of rouleaux formation, implicates an increase in plasma gamma globulin.
Further studies include a bone marrow examination, where at least 30% of bone marrow cells should be variations of mature and immature plasma cells. Serum protein electrophoresis will reveal a monoclonal globulin spike, and light chains over 1.0 gm/24 hours may be seen in the urine. The presence of lytic bone lesions is a convincing clinical clue. With these findings in combination, a diagnosis of myeloma can be made with assurance.
