December 24, 2021
B-Cell Lymphoma Muscle Mass
Figure 1: Hematoxylin and eosin stained frozen section
Sections demonstrate the presence of variably atrophic muscle fibers (including basophilic regenerating and necrotic muscle fibers) entrapped within a background cellular infiltrate composed of atypical mononuclear cells with enlarged nuclei and relatively sparse cytoplasm.
This 70-year-old patient presented with generalized muscle weakness, weight loss, decreased appetite, mild hypercalcemia, and a 2-month history of progressive right elbow swelling. The patient’s past medical history was significant for gout. Laboratory studies showed elevated ESR (80s-90s). The patient was treated with steroids prior to muscle biopsy and reported significant improvement. Muscle biopsy was performed to evaluate for myopathy.
What is your diagnosis based on Figures #1 through #4?
B. Pyogenic myositis
D. B-cell lymphoma
Figure 2: Hematoxylin and eosin stain paraffin section
Areas of geographic necrosis are present (left image). The nuclear detail is better demonstrated in formalin-fixed paraffin embedded tissue sections (right image) , and shows that the atypical cells have single to several prominent nucleoli.
Figure 3: CD20 (left) and CD3 (right) immunohistochemical stains
The atypical neoplastic cells show strong diffuse membranous staining for CD20, a marker of B-cell differentiation. Scattered admixed CD3-positive T-cells are present.
Figure 4: CD20 (left) and CD3 (right) immunohistochemical stains
The proliferative fraction, as demonstrated with KI67 (a marker of cell proliferation present in G1, S, G2, and mitotic phases, but absent in G0 resting phase) is very high.
Answer: B-cell lymphoma
The morphologic and immunophenotypic features are consistent with the presence of a “B-cell lymphoma”; specifically Diffuse Large B-cell Lymphoma (DLBCL). Further studies are needed to provide additional prognostic and predictive information, and guide treatment; including immunostains (i.e. Hans algorithm: CD10, BCL6, and MUM1 to determine cell of origin (GCB/germinal center B-cell-like versus ABC/activated B-cell-like subtypes), and Fluorescence In-Situ Hybridiation (FISH) to evaluate for cytogenetic rearrangements involving MYC [IGH-MYC t(8;14)], BCL2 [IGH-BCL2 t(14;18)(q32;q21)], and BCL6 [3q27 gene rearrangement].
More recently DLBCL subtypes are being further investigated using gene expression profiling, next-generation sequencing, and copy number variation type assays.
The lymphoid cells are atypical – rather than mature appearing as would be expected in polymyositis, and are present as a dense infiltrate of B-cells which nearly replaces the skeletal muscle tissue. No neutrophils are seen to suggest that this represents pyogenic/bacterial myositis. Granulomata characteristic of sarcoidosis are not present.
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