PMC7365499_01
(a) Photomicrograph of normocellular bone marrow trephine biopsy (H and E, x40). (b) Numerous histiocytes replacing the other normal bone marrow cell constituents (H and E, x100)
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F1
The marrow was normocellular for the age [Figure 1a]. The rest of the marrow hematopoietic elements were suppressed [Figure 1b].
(a) Hemophagocytosis (arrows) (H and E, x400). (b) Brown-colored pigment in the histiocytes (arrows) (H and E, x200)
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F2
Many of these marrow macrophages demonstrated phagocytosis of red cells, white cells, platelets as well as immature myeloid and erythroid cells (hemophagocytosis) [Figure 2a]. Some of these histiocytes also revealed the presence of a brown-colored pigment [Figure 2b].
Photomicrographs of immunohistochemistry revealing (a) Positive cytoplasmic immunoexpression of CD68 in histiocytes (CD68, x200). (b) CD1a-negative histiocytes (CD1a, x200). (c) Negative immunoexpression of histiocytes for S100 (S100, x200). (d) CD3 immunopositive expression of the lymphocytes (CD3, x200)
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F3
On IHC, the histiocytes were positive for CD68 and negative for CD1a, S100, CD3, CD20, epithelial membrane antigen, and pancytokeratin, confirming the histiocytic nature of these large cells and ruling out the possibility of dendritic cell-related (Langerhans cell histiocytosis) and malignant histiocytosis [Figure 3a-c]. However, on IHC, a finding that was evident was the CD3 positive immunoexpression of the increased lymphocytes [Figure 3d].
(a) Periodic acid-Schiff stain negative histiocytes (PAS, x200). (b) Perl's Prussian blue staining showing unstained brown pigment in the histiocytes (Perl's stain, x200)
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F4
These histiocytes were negative for both the PAS stain as well as the Oil red O stain [Figure 4a], thus ruling out any storage histiocytosis. Another finding that was revealed on Perl's iron stain was that not all histiocytes containing the brown pigment demonstrated hemosiderin, and in most of them, the brown pigment remained unstained [Figure 4b].
(a) Schizont of P. vivax (encircled) on peripheral blood smear examination (Leishman stain, x200). (b) Bleaching of the brown-colored pigment in the histiocytes with the alcoholic ammonium hydroxide (H and E, x200)
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F5
The peripheral smear revealed fragmented red blood cells and on careful examination, schizonts of P. vivax [Figure 5a]. Meanwhile, the trephine biopsy was treated with alcoholic ammonium hydroxide, to which the brown pigment responded by getting bleached, hence, confirming the nature of this pigment to be that of malarial pigment (hemozoin) [Figure 5b].