Are micromegakaryocytes specific for refractory cytopenia of childhood (RCC)? A study of 38 pediatric patients with thrombocytopenia unrelated to RCC

• Micromegakaryocytes are characteristic ofrefractory cytopenia of childhood (RCC).
• No threshold is established for number of micromegakaryocytes for RCC.
• We identified micromegakaryocytes in non-myelodysplastic syndrome/RCC cases.
• Hence the need for establishing the threshold for micromegakaryocytes for RCC.

BackgroundMicromegakaryocytes (microMKs) are considered the most reliable dysplastic feature for myelodysplastic syndrome (MDS), particularly refractory cytopenia of childhood (RCC); there is no minimal threshold for the diagnosis of RCC. Since most RCC patients present with thrombocytopenia, the presence of microMKs should raise concern for MDS/RCC. This study attempted to investigate the prevalence of microMKs and associated marrow fibrosis in patients with thrombocytopenia unrelated to MDS/RCC and the need for establishing a threshold for microMKs for the diagnosis of MDS/RCC.DesignBone marrow biopsies of pediatric patients with thrombocytopenia unrelated to RCC were examined for microMKs and fibrosis by CD61 immunohistochemical and reticulin stains respectively.ResultThirty eight patients (1–18 years old) were included: 33 immune thrombocytopenia (ITP), 3 chronic thrombocytopenia, and 2 inherited macrothrombocytopenia. Fourteen cases (37%) had microMKs; four cases showed increased marrow fibrosis associated with microMKs (two had ITP and two had macrothrombocytopenia). All patients are alive and none developed MDS (follow up: 3months to 4 years).ConclusionMicroMKs can be seen in pediatric patients with thrombocytopenia unrelated to RCC. Hence the mere presence of microMKs is insufficient for the diagnosis of RCC in the pediatric population, and a quantitative threshold needs to be established.