Clinical Pathology: General Principles, Hematology & Coagulation, Immunology & Histocompatibility, Urinalysis, Body Fluids, Clinical Microscopy, Genetic Testing

476) A 3-week-old boy with trisomy 21 is taken to his pediatrician for a checkup. He has been a healthy and happy baby since birth. The parents have no concerns at this time. Routine blood work is done that shows marked leukocytosis and thrombocytopenia. The peripheral smear is shown in the figure. Which one of the following statements is true?

• Transient abnormal myelopoiesis (TAM) occurs in approximately 10% of newborns with trisomy 21.

• There is an abnormal proliferation of myeloid precursors, typically megakaryocytes. CD61 immunohistochemistry can be useful is assigning the megakaryocytic lineage to such cells in tissue sections.

• TAM will typically resolve spontaneously within the first few months of life. Organomegaly and liver disease occur in a significant proportion of these patients and can be fatal. Only in such a circumstance would aggressive chemotherapy be warranted. Other patients can be completely asymptomatic.

• There is a substantial risk (20% to 30%) for the development of nontransient acute leukemia within the first 3 years of life in patients with TAM. The preleukemic phase can be associated with dysplasia and features of refractory cytopenia of childhood.

• The prognosis of acute myeloid leukemia (AML) in this setting (typically associated with GATA-1 mutation) is better than in cytogenetically normal children.

• Other clinical features include thrombocytopenia, vesicular skin disease, marrow fibrosis (teardrop cells), and if in utero, hydrops fetalis.

• Patients with trisomy 21 have an increased incidence of all types of leukemia in all age groups.

Brink DS: Transient leukemia (transient myeloproliferative disorder, transient abnormal myelopoiesis) of Down syndrome.Adv Anat Pathol 2006;13(5):256–262.

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