Extramedullary Plasmacytoma: A Localized or Systemic Disease?

TO THE EDITOR:

Extramedullary plasmacytoma is an uncommon variant of plasma cell dyscrasia that develops outside the bone; most cases (76%) occur in the upper respiratory tract [1]. Lung involvement is rare; only 20 cases have been reported [2]. For the definition of primary extramedullary plasmacytoma, a normal radiographic survey in the absence of bone marrow infiltration is required. The latter criterion has classically been assessed by conventional morphology. Now, however, more sensitive approaches are available for the identification of bone marrow involvement. These studies would help elucidate whether extramedullary plasmacytoma is a localized or an already disseminated disorder.

A 70-year-old man with episodes of recurrent pneumonia had radiographic evidence of opacity in the lower right lobe of the lung. The IgG-λ serum monoclonal component was 60.45 g/L, and no Bence Jones urinary protein or skeletal lesions were present. Bone marrow aspirate revealed less than 1% of plasma cells, as seen with May-Grunwald-Giemsa staining. Computed tomography of the chest confirmed a mass, the histology of which confirmed a proliferation of IgG-λ-secreting plasma cells with amyloid deposits.

Our patient met the criteria for secretory primary pulmonary plasmacytoma [2]. However, flow cytometric analysis using a propidium iodide/CD38 double-staining technique [3] showed that all plasma cells displayed DNA aneuploidy (DNA index, 1.10; Figure 1). On deparaffinized tissue blocks obtained from the pulmonary mass, DNA measurements by flow cytometry detected a clonal aneuploid population of plasma cells (DNA index, 1.10), and cytogenetic studies with fluorescence in situ hybridization [4] detected a trisomy of chromosome 1. The identical DNA index seen in plasma cells from both the mass and the bone marrow suggests that these cells may belong to the same clone.

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Figure 1. Samples were simultaneously stained for propidium iodide and CD38+; plasma cells (CD38+ cells, black dots) show a higher DNA content than do other cells (gray dots) in the same phase of the cell cycle. FITC = fluorescein isothiocyanate. Results of flow cytometric analysis of extramedullary plasmacytoma.

To our knowledge, no information about cytogenetics or DNA cell content characteristics of tumor plasma cells has been reported for patients with extramedullary plasmacytoma. Our findings indicate that the DNA pattern in primary pulmonary plasmacytoma is similar to that previously seen in multiple mycloma [5]; in this condition, both DNA hyperploidy and trisomy 1 are common. An additional important finding in our patient was the detection of clonal plasma cells in the bone marrow even though few normal-appearing plasma cells were seen by morphology. In summary, our results suggest that when appropriate and sensitive techniques are used, some, if not all, patients with extramedullary plasmacytoma may be found to have disseminated disease. This would indicate that both extramedullary plasmacytoma and multiple myeloma are part of a continuous spectrum of plasma cell disorders rather than separate entities.

• Copyright ©2004 by the American College of Physicians