Severe Transient Abnormal Myelopoiesis: A Report of 2 Cases.

Transient abnormal myelopoiesis (TAM) occurring in infants with trisomy 21 self-resolves in >90% of cases. In a few infants, there is extensive myeloid proliferation which leads to life threatening symptoms and occasionally fatal outcome. The clinical features of such "high risk" infants have been described, but the diagnosis of "severe" or "high risk" TAM remains underutilized, and their pathologic findings are not widely reported. In this report we describe 2 cases of severe TAM that led to an early demise of these infants and discuss the histological and immunophenotypic findings, as well as the value of designating TAM as severe if the clinical scenario is appropriate. The findings of hepatomegaly, hyperleukocytosis, and liver dysfunction commonly reported in severe TAM were also present in the 2 infants. Dysplastic megakaryocytes typically seen in Down syndrome-Myeloid leukemia were frequently noted in liver infiltrates.