LAUSR

A 32yearold woman with no previous medical history was admitted to the haematology unit with weakness and dyspnoea. Physical examination found cervical adenopathy and diffuse purpuric lesions. The blood count showed anaemia (haemoglobin 105 g/L), severe thrombocytopenia (platelet count 39 × 109/L), leukocytosis (white cell count 80 × 109/L) and blood smear revealed circulating blast cells and monocytosis. Bone marrow aspirate allowed the diagnosis of acute myelomonocytic leukaemia with morphology suggesting a CBFB/MYH11 fusion transcript. Surprisingly, some mature neutrophils showed bundles of Auer rods (May– Grünwald– Giemsa stain, ×100 objective). Flow cytometry analysis confirmed this myeloidtype blast proliferation expressing CD13, CD33 and intracytoplasmic myeloperoxidase antigens. This population also shows maturation into monocytes expressing CD45, CD14, CD64 and CD36 antigens. Conventional cytogenetic analysis revealed a pathological clone with an inv(16)(p13.1q22) and PCR analysis detected the presence of a CBFB::MYH11 fusion transcript and ruled out the PML::RARA rearrangement. The diagnosis of acute myeloid leukaemia (AML) with inv(16)(p13.1q22) according to the WHO classification was made and the patient received appropriate chemotherapy, achieving a complete remission after induction. Bundles of Auer rods in blasts is usually regarded as a morphologic clue to the diagnosis of acute promyelocytic leukaemia (APL) with PML::RARA fusion transcript, with their presence in mature granulocytes occurring during alltrans retinoic acid treatment. Bundles of Auer rods observed in only neutrophils are an extremely rare observation that is reported in few cases in the literature mainly in association with core binding factor lesions. This case of AML with inv (16)(p13.1q22) and unusual bundles of Auer rods emphasises the importance of the multidisciplinary diagnosis including morphology, immunophenotyping, and cytogenetic and molecular analyses.