Histologic and immunohistochemical study of bone marrow monocytic nodules in 21 cases with myelodysplasia

Previously, 4 cases of myelodysplastic syndrome were reported that had unusual, distinct monocytic nodules in bone marrow. The monocytic nodules, predominantly composed of monocytes with CD68+ immunostaining, had no or low expression of Ki-67 and topoisomerase II alpha. The purpose of the present study was to further define the associated clinical diseases, histologic features, and immunohistochemical characteristics of 21 such cases. Relevant hematopathologic slides of all cases were reviewed, and extensive immunohistochemical staining was performed. Most patients (15/21 [71%]) had monocytosis in the bone marrow, and chronic myelomonocytic leukemia was the most commonly associated clinical disease. In 4 patients, the monocytic nodules also were present in lymph node, spleen, or skin. Immunohistochemical staining results for the monocytes in the nodules were similar to those for plasmacytoid monocytes. Our study established that monocytic nodules can be present in myelodysplastic syndromes, myeloproliferative diseases, and acute myeloid leukemia; verified the monocytic lineage; and revealed the low proliferative state of these cells.