Microscopic Description -- Intermittent Confusion, Fever of Unknown Origin, and Lower Extremity Weakness


Peripheral blood:
The peripheral blood smear demonstrates clusters and individual atypical lymphoid cells (Figs 1 & 2). These lymphoid cells are large with scant to moderate amounts of basophilic cytoplasm, which is occasionally vacuolated, prominent nucleoli and rounded or convoluted nuclear contours (Fig 1).

Bone marrow aspirate and biopsy:
In the marrow, erythroid maturation is mildly megaloblastoid. Myeloid maturation is megaloblastoid with retention of primary granules (Aspirate, Fig 3). An interstitial as well as intravascular infiltration of large lymphoid cells with irregular nuclear contours and prominent nucleoli is seen in the biopsy (Figs 4, 5). Immunohistochemical stains performed on the biopsy demonstrate that the large cells are positive for CD45/LCA, CD20/L26 (Fig 5), CD 22, and negative for CD3, CD30/Ber H2, AE1/AE3 (cytokeratins) and Factor VIII (Figs 6, 7). The Factor VIII staining, which stains the endothelial cells, highlights the intravascular location of the lymphoid cells.

Skeletal muscle:
Hematoxylin and Eosin (H&E) stained sections demonstrate blood vessels containing atypical mononuclear cells with irregular nuclear contours and some mitotic figures (Fig 8). Some of these cell clusters completely fill the lumen. The atypical intravascular mononuclear cells show strong immunoreactivity for CD20 (Fig 9), weak to moderate reactivity to CD45, and no reactivity for CD3. Infrequent, perivascular CD3+ cells are noted around several small vessels without atypical luminal aggregates.

Sural nerve:
The teased never fiber preparation shows extensively early axonal degeneration and mild segmental demyelination. H&E stained sections reveal intravascular atypical mononuclear cells in the epineurium (Fig 10). Immunohistochemical stains show reactivity of the intravascular cells for CD20 (Fig 11) and weak reactivity for CD45. CD3 stain is negative.





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