Comparison of severe aplastic anaemia and lower risk hypoplastic myelodysplastic neoplasms: Critical role of megakaryocyte count in distinguishing aplastic anaemia from myelodysplastic neoplasms.

Although genetic abnormalities are increasingly crucial for diagnosing and classifying haematopoietic diseases, dysplasia remains crucial for distinguishing myelodysplastic neoplasms (MDS) from aplastic anaemia (AA). Erythroid dysplasia may be observed in AA, complicating the differentiation between these conditions. In a previous study using the data from the Japan Idiopathic Myelodysplastic Syndrome Study Group's registry, we found that erythroid dysplasia does not affect the prognosis of AA. This current study was designed to compare the prognosis of patients with lower risk hypoplastic MDS (LR-hMDS), as determined by our review, and patients with severe AA (SAA), all enrolled concurrently, to validate our diagnostic approach. Stringent criteria were used to rule out MDS, considering bone marrow cellularity and megakaryocyte counts, with a confirmed AA diagnosis only following a reduced megakaryocyte count. The study comprised 39 severe cases extracted from a cohort of 100 AA patients previously reported and 41 patients with LR-hMDS. Significant differences in overall and leukaemia-free survival were observed between the two groups (p < 0.0001). Even among patients undergoing immunosuppressive therapy, a marked prognostic distinction became evident after 5 years, although their response to the therapy did not differ significantly. Therefore, the megakaryocyte count is pivotal in differentiating MDS from AA.