PMC8373504_01
Bone marrow biopsy with foamy Mott cells on (a) H&E immunostain for (b) CD68 highlights scattered smaller cells of macrophage-monocyte lineage, but are negative in the larger foamy cells; however, they are positive for (c) CD138 and (d) kappa, confirming their plasmacytic differentiation. Note that the cytoplasmatic kappa IHC pattern matches the inclusions seen on H&E. (e) Bone marrow aspirate smear (Wright stain). (f) Posttherapy bone marrow biopsy, lambda light chain. Trephine biopsy cells original magnification 200x; aspirate smear (cell (E)) original magnification 1000x.
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fig1
Numerous large cells with foamy cytoplasm, resembling foamy macrophages or Gaucher cells (Figure 1(a)), were identified. The large cells stained negative for CD68 PGM1 (Figure 1(b)), periodic acid-Schiff (PAS), and both cytokeratin AE1/AE3 and MNF116. They showed strong positive cellular membrane staining for CD138 (Figure 1(c)); the staining for kappa light chain was positive, cytoplasmatic, in 60% of the marrow nucleated cells (Figure 1(d)), whereas lambda light chain was positive in isolated cells only (<1%). On follow-up, bone marrow biopsy was performed in December 2015 (7 months after initial presentation), the large vacuolated cells comprised only 5% of the cellular marrow (Figure 1(e)). This population was positive for lambda light chain (Figure 1(f)).