Introduction

Systemic mast cell disease is characterised by abnormal proliferation and accumulation of mast cells in bone marrow or other non-cutaneous organs.1 The abnormal proliferation of mast cells is also associated with other haematological disorders, classified as systemic mastocytosis with associated clonal haematological non-mast-cell lineage disease (SM-AHNMD). However, the presence and dysplasia of mast cells can easily be overlooked during routine bone marrow examination. Therefore, the laboratory staff and oncologists in our hospital decided to specifically stain mast cells with toluidine blue in bone marrow aspirate specimens of patients suspected to have different types of systemic mastocytosis (SM), or other clonal haematological disorders, such as myelodysplastic syndromes (MDS), thereby reducing the chance of missing the increased presence and dysplasia of mast cells in bone marrow specimens.2

MDS are classified by the WHO as myeloid neoplasms, and are characterised by cytopenia and dysplasia in one or more myeloid cell lines.3 This is a result of ineffective haematopoiesis and leads to increased risk of development of acute myeloid leukaemia. To establish the diagnosis of MDS can be challenging, particularly for low-grade MDS.4 Therefore, new diagnostic tools—for example, flow cytometry, to facilitate low-grade MDS diagnosis are needed.

In our laboratory, since the introduction of toluidine blue staining of bone marrow specimens, we have frequently found an increased number of mast cells, often showing dysplasia, in bone marrow aspirates of patients suspected to have MDS. To investigate whether this finding might be helpful in the diagnosis of MDS, we analysed whether the number and dysplasia of mast cells were indeed increased in patients diagnosed with MDS. Interestingly, we found that mast cell numbers and dysplasia …