| Session: Extramedullary manifestation of neoplastic myeloid disorder |
| Case number: 130 |
Submitter(s): Karen L. Grogg, James D. Hoyer, William G. Morice.
Clinical history
74 year-old woman without significant past medical history presented with diffuse lymphadenopathy and progressive pancytopenia. An axillary lymph node was excised. Over the next four weeks, the patient was treated with prednisone. Follow-up CBC then showed WBC 84x10^9/L, Hgb 10 g/dL, MCV 98.3 fL, plt 42x10^9/L. White blood cell manual differential (%): Neutrophils 18, Lymphs 12, Monos 20, Metamyelocytes 1, Myelocytes 4, Blasts/promonocytes 45. A bone marrow biopsy was performed.
Details of gross/microscopic pathology:
Lymph node: Paracortical infiltrate of medium sized cells with reniform nuclei, moderately condensed chromatin, and abundant pale eosinophilic cytoplasm. No morphologically immature cell population identified.
Bone marrow: Markedly hypercellular with 60% blasts and promonocytes having round to delicately folded nuclear contours, finely dispersed chromatin, and sparse agranular cytoplasm. Scattered cells within the infiltrate possessed more abundant cytoplasm and condensed chromatin, morphologically similar to those in the lymph node.
Immunophenotype (flow cytometry/immunohistochemistry):
Lymph node: By paraffin immunohistochemical studies, the neoplastic cells expressed S100 (strong), CD68 (PGM1), lysozyme, bcl-6, CD4, CD43, CD33 (weak, focal) and CD45 (weak). CD163 staining highlighted distinct dendritic cell morphology in a subset of the cells in the paracortical infiltrate. They lacked expression of CD1a, myeloperoxidase, CD34, CD117, CD123, TCL1, Melan A, and tyrosinase.
Bone marrow: By flow cytometry, 20% of the cells fell into a classical blast gate (CD45 and side light scatter). These cells expressed CD7, CD13, CD33 (dim), CD34, CD117 and HLA-DR. An additional 40% of the cells had CD45 and side light scatter properties typical of monocytes. These cells were CD34 negative; they expressed CD13, CD33, CD14, CD117, and HLA-DR. Both populations were negative for CD1a, CD11c and a number of other T- & B-cell associated antigens.
By paraffin immunohistochemical studies, a subset of cells in the marrow infiltrate expressed S100 and bcl-6. No expression of CD1a was seen.
Cytogenetics:
Cytogenetic analysis on the bone marrow aspirate specimen showed a normal female karyotype (46, XX) in 20 of 20 metaphases analyzed.
Molecular analysis:
Interesting feature(s) of submitted case:
Although collections of mature monocytes/plasmacytoid monocytes have been reported in lymph nodes as extramedullary manifestations of acute or chronic myelomonocytic neoplasms, differentiation to an interdigitating dendritic cell morphology and phenotype has not been described. Interdigitating dendritic cell tumors show a widely variable clinical behavior, with some cured by simple excision and others pursuing a rapidly fatal course. The current case suggests that the more aggressive subgroup may in fact represent an extramedullary manifestation of acute myeloid leukemia.
Proposed diagnosis:
Acute myelomonocytic leukemia, with extramedullary differentiation to interdigitating dendritic cell tumor.
Panel diagnosis:
no consensus diagnosis; see comment
Comments:
Panel comment/stains: Macrophage differentiation, macrophage dendritic morphology (BCL6+, CD163+). Additional information from the submitter: image of an immunostain for CD163 on the bone marrow core bx included (Figure 10). When I submitted the case, I didn't have this stain to correspond to the one on the LN. I thought it was interesting that the CD163 shows a pattern in the bone marrow similar to S100; most of the blasts are negative, a small subset of blasts shows weak positivity, and a population with dendritic processes shows strong staining. It seems to support the idea of a cell spectrum with differentiation toward an interdigitating dendritic cell-like population.
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