Background: Although acute promyelocytic leukemia displays a wide spectrum of morphological variants, the classic morphological variants are defined as hypergranular variants and the hypogranular or microgranular form.
Methods: We report here for the first time a rare morphological variant of APL mimicking myelodysplastic syndrome. A 49-year-old man presented with pancytopenia. Laboratory findings were as follows: White blood cell count was 1.39 x 109/L, hemoglobin was 120 g/L, platelet count was 103 x 109/L, fibrinogen was 3.42 g/L and D-dimer was 3.14 mg/L. Peripheral blood smear revealed no blast or immature cells. Very careful inspection of bone marrow smears indicated 5% blast cells, of which 50% had hyperbasophilic cytoplasm and obvious cytoplasmic blebs mimicking megakaryoblasts or micromegakaryocytes, the others were promyelocytes with obvious bilobed nuclei and fine azurophilic granules. One or a few Auer rods could be seen in 0.5% of the blasts. Myeloperoxidase was strongly positive in the blast cells. Immunophenotyping of the BM revealed an abnormal myeloid population, which was negative for CD34 and HLA-DR. Cytogenetic analysis of the bone marrow cells revealed a 46,XY,t(15;17)(q24;q21)/46,XY karyotype, and the PML-RARA fusion gene was positive.
Results: The patient was diagnosed with acute promyelocytic leukemia according to WHO classification.
Conclusions: The patient was initially diagnosed with myelodysplastic syndrome with excess blasts 2 based on cytological features. Due to the need for specific emergency treatment to avoid the risk of potentially fatal bleeding, recognition of the distinctive morphological features is vital for the diagnosis and prognosis of APL.