Case 411 -- A Solitary Bone Lesion

Contributed by Teresa LaCaria, MD, Karen Schodel , MD
Published on line in December, 2004


The patient was male in his 60s with a history of monoclonal gammopathy of undetermined significance, who presented with borderline normocytic anemia. Peripheral blood showed hemoglobin 12.4 g/dL, hematocrit 36.3 percent, MCV 86.6 fL, MCH 29.6 pg, and MCHC 34.2 g/dL.

He underwent a bone marrow aspirate and biopsy for evaluation of multiple myeloma or other etiology for his anemia. The marrow demonstrated trilineage hematopoiesis with no evidence of plasma cell neoplasm, and adequate erythroid precursors [Figure 1]. Rare lymphoid aggregates were noted in the marrow [Figure 2]. A single paratrabecular aggregate showed approximately equivalent numbers of B cells and T cells, rather than the T-cell predominance expected of a reactive lymphoid aggregate.

The relative predominance of B cells and the atypia raised the possibility of a B cell lymphoproliferative process, thus additional analyses were performed. Immunohistochemical stains for kappa and lambda light chains, CD138, CD20, CD10, and others showed no aberrant B cell phenotype. The marrow biopsy was positive for both kappa and lambda. However, the lymphoid aggregate of interest was poorly represented on the sections available for staining. Flow cytometry revealed less than 1 percent CD138 positive plasma cells, with no evidence of a clonal or phenotypically abnormal lymphoid population. Flow cytometry results were questionable, however, because few B cells were present in the specimen. Cytogenetic studies demonstrated an apparently normal male bone marrow without numerical or structural chromosomal abnormalities. The significance of the lymphoid aggregate remained undetermined.

Approximately 1 month later, an 8.4 cm lytic lesion involving the right acetabulum and ilium was discovered [Figure 3]. A radiographic body survey showed no other lytic lesions. The site was biopsied, and histologic sections demonstrated sheets of mature plasma cells [Figure 4]. Immunohistochemical stains showed numerous plasma cells with kappa and CD138 positivity, and only scattered cells with lambda positivity [Figures 5]. Flow cytometry was attempted, but yielded mostly non-specific staining.


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