A 67 year male presented with pallor and generalized weakness of 1 month duration. The peripheral blood examination showed macrocytic red cells with the presence of 30 nRBC cells/100 white blood cells. Biochemical investigations were unremarkable except for elevated S. LDH levels (2747U/L). Coombs test was negative. FDG PETCT showed mild diffuse FDG activity in the bulky spleen and bone marrow. Bone marrow aspiration was aparticulate and dilute, however, the imprint smears and biopsy showed a cellular marrow completely replaced by a discrete monomorphic population of ovoid to spindle cells with fine chromatin, inconspicuous nucleoli, shallow nuclear clefts, and a moderate amount of pale cytoplasm (Fig. 1a–c and inset 1a, o.m. 100×). Flow cytometry immunophenotyping on the dilute aspirate sample showed ~ 2% clonal plasma cells positive for CD138, CD38, CD200 and lambda light chains; negative for CD45 CD19, CD56, and CD81 (Fig. 1d). Subsequently, immunohistochemistry performed on the biopsy specimen showed tumor cells to be positive for CD138 and negative for numerous other mesenchymal and epithelial markers, namely vimentin and cytokeratin (Fig. 1e). Intriguingly, there was an absence of monoclonal protein on serum protein electrophoresis (SPE), however, immunofixation electrophoresis (IFE) showed a lambda light chain monoclonal protein (Fig. 1f) and the serum free light chain analysis revealed κ: λ ratio of 0.006. A final diagnosis of spindle cell variant of myeloma was offered.
Fig. 1.
Panel of photographs representing the diagnostic armamentarium, a MGG stained imprint smears showing the atypical ovoid to plump cells with moderate amount of pale blue cytoplasm, opened up chromatin and shallow clefting as seen in the inset, b, c hematoxylin and eosin stained bone marrow biopsy showing diffuse replacement of normal marrow by these atypical plasma cells (o.m. × 10× and 100×), d Flow cytometry dot plots depicting the clonal plasma cells, e pan-reactivity for CD138 by immunohistochemistry on bone marrow biopsy, f lambda light chain restriction confirmed by immunofixation electrophoresis (IFE)
Spindle cell variant of myeloma is rarely reported in the literature and mimics sarcomas, spindle cell lymphomas and neuroendocrine tumors [1, 2]. Cognizance of this ‘de-differentiated’ variant is essential particularly in cases where 18F-FDG PET/CT and SPE are non-contributory in diagnosis.
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References
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