Refractory cytopenia of childhood (RCC) is subdivided into myelodysplastic syndrome with multilineage dysplasia (MDS‐MLD) and RCC without (w/o) multilineage dysplasia (RCC without MLD). Although RCC is a histomorphological distinct entity, the bone marrow (BM) histology of RCC is not yet characterised in relation to multilineage dysplasia. We investigated the BM histological features of RCC to clarify the characteristics of BM histology of MDS‐MLD in childhood compared to RCC without MLD.

The BM histology and cytology in 60 RCC patients from the nationwide registry of Japanese Childhood AA‐MDS Study Group were reviewed retrospectively. Although a thorough genetic assessment, including GATA2 and/or SAMD9, was not performed, inherited BM failure disorders were excluded by a cytogenetic test, a chromosome fragility test and a telomere length measurement along with careful clinical assessments. Among the 60 patients, 20 (33%) of MDS‐MLD and 40 (67%) of RCC w/o MLD were classified according to their BM cytology. We then investigated the BM histological features and compared them between the two groups. The BM cellularity, distribution pattern of haematopoiesis, frequency of left‐shifted granulopoiesis, numbers of micromegakaryocytes and p53 immunostaining‐positive cells were significantly different between the groups. The BM histology of MDS‐MLD in childhood showed higher cellularity, the more common occurrence of diffuse distribution pattern, more frequently left‐shifted granulopoiesis and more micromegakaryocytes and p53 immunostaining‐positive cells than RCC without MLD.

Our results showed that MDS‐MLD in childhood had a characteristic BM histology compared to RCC without MLD. The clinical relevance of MDS‐MLD in childhood needs to be evaluated.