Bone marrow mast cell morphologic features and hematopoietic dyspoiesis in systemic mast cell disease

Systemic mast cell disease (SMCD) cannot be distinguished from reactive mastocytosis (RM) by quantitation of mast cells in aspirate smears, and few studies have analyzed systematically the morphologic features of mast cells in SMCD vs RM. In addition, although SMCD is associated with myeloproliferative disorders/myelodysplastic syndromes (MPD/MDS), it is not known whether subtle signs of dysplasia or MPD can be found in SMCD, suggesting most cases are part of a dysplastic or myeloproliferative process. We compared 18 bone marrow specimens with SMCD with 10 bone marrow specimens from patients with RM. Mast cells in SMCD were more likely to show cytoplasmic hypogranularity, uneven granule distribution, and fusiform morphologic features. Eight cases of SMCD (44%) demonstrated MPD/MDS, and 9 cases (50%) showed subtle evidence of dyspoiesis, with megaloblastic change, nuclear budding of erythroid precursors, and/or atypical megakaryocytes. Mast cells in SMCD appear morphologically different from those in reactive proliferations. Dyspoietic features were present in most cases of SMCD, suggesting that SMCD is part of a spectrum of chronic myeloproliferative/myelodysplastic disorders.