Auer Rods in Chronic Myelomonocytic Leukemia Can Change the Diagnosis

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder with overlapping morphological features of myelodysplastic and myeloproliferative disease and a potential risk of transformation to acute myeloid leukemia. Presence of Auer rods in CMML is a rare finding and the presence of an occasional Auer rod gives the diagnosis of CMML-2 in spite of the presence of <5% blasts in peripheral blood/bone marrow [1,2]. A 39-year-old female, diagnosed outside our facility with Crohn’s disease, presented with severe anemia with weakness and fatigue for 1 month. The patient had been treated previously with prednisolone at 1 mg/kg/day. Diarrhea was resolved after 2 weeks of therapy. Steroid dose was reduced and stopped after 4 months. There were no bowel symptoms and the colonoscopy done at our institution was normal. Hemoglobin was 65 g/L, total leukocyte count was 16.4x109/L, and platelet count was 192x109/L. Peripheral blood smear showed 4% blasts and promonocytes, 3% myelocytes and metamyelocytes, 26% monocytes (including abnormal forms) (Figures 1A and 1B), and 2 nucleated red blood cells/100 white blood cells. Bone marrow aspirate was hypercellular with dyspoiesis in all 3 lineages with increased monocytic cells (Figures 1C and 1D). Erythroid series showed predominantly megaloblastoid erythropoiesis with nuclear budding, multinuclearity, and cytoplasmic vacuolation. Granulocytic series showed myeloid hyperplasia with 15%-20% monocytes, 2% basophils, and 4% blasts, with an occasional blast showing an Auer rod (Figure 1C, arrows). Micromegakaryocytes and megakaryocytes with abnormal lobation and multinucleation were seen. Bone marrow biopsy was hypercellular (100%) with grade 1 reticulin fibrosis. Megakaryocytes were increased in number and showed hypolobation and multinucleation. Conventional cytogenetics showed a normal female karyotype. There was no Philadelphia chromosome or BCR/ABL fusion gene. Overall features were compatible with a diagnosis of CMML type 2. She was started on 3+7 induction chemotherapy using daunorubicin and ara-C. Bone marrow aspirate done on day 28 confirmed morphological complete remission. She underwent HLA-identical allogeneic hematopoietic stem cell transplantation from her elder brother and currently (2 years posttransplant) continues to be disease-free. Auer rods are a hallmark of acute myeloid leukemia but are occasionally seen in myelodysplastic syndrome (refractory anemia with excess blasts type 2) or CMML cases, and rarely in patients with fewer than 5% blasts [3,4]. According to the World Health Organization 2008 diagnostic criteria, the presence of Auer rods fulfills the criteria for CMML-2 irrespective of the blast count [5]. Thus, in CMML, a thorough search for Auer rods should be done for a correct diagnosis as the treatment given for CMML-2 is different from that for CMML-1 and the risk of transformation to acute leukemia is greater. We also want to emphasize that the presence of Auer rods with fewer than 5% blasts is a rare phenomenon that seems to be clinically, morphologically, and cytogenetically heterogeneous, and it could be a valuable finding for early treatment options in patients with CMML-2 if there is a HLA-identical donor. Conflict of Interest Statement The author of this paper has no conflict of interest, including specific financial interests, relationships, and/ or affiliations relevant to the subject matter or materials included in this manuscript.