Acute promyelocytic leukemia masquerading as myeloid maturation arrest- A Case report.

Acute promyelocytic leukemia (APL) is a medical emergency. The diagnosis of APL requires morphological examination, cytochemistry, immunophenotyping, and reverse transcriptase polymerase chain reaction (RT-PCR) for PML::RARA or its variants. However, due to the rapid development of complications, diagnosis often relies on morphology and cytochemistry for early treatment. Herein, we describe a 72-year-old gentleman who presented with pancytopenia diagnosed as acute promyelocytic leukemia with an unusual morphology. The bone marrow smear showed 80% myelocyte-like cells with prominent granules and maturation arrest, with an occasional neutrophil. On careful re-examination of the peripheral smear and bone marrow, an occasional poorly preserved cell with a bundle of Auer rods was identified. Cytochemistry for MPO was strongly positive in abnormal promyelocytes and flow cytometry showed positivity for MPO, CD13, CD33, and CD117 and was negative for CD34 and HLA-DR. Cytogenetics showed a complex karyotype of 45,XY, -14, t(15;17)(q24;21)t(14;21)(q11.2;p13)[10]/ 45, XY, idem, add(5)(q35)[5]/ 45,X,-Y[5]. RT-PCR for PML-RARA was positive for the bcr-3 transcript and FISH was positive for t(15;17) (q24;q21). The take home point from our case is to look for the presence of cells with bundle of Auer rods whenever there is pancytopenia with the presence of myelocyte-like cells with prominent granulations.