Case Presentation: A 73-year-old male with a history of Crohn’s disease presented to an outside hospital with exertional shortness of breath and palpitations. He was treated for symptomatic anemia secondary to vitamin B12 deficiency. He was then referred to our hospital due to the presence of rare blasts on blood smear. Upon arrival, he was hemodynamically stable but found to have pancytopenia with a WBC 1.76 K/μL, Hgb 9.0 g/dL, MCV 110.2 fL, and platelets 34 K/μL. Physical exam was unremarkable and did not show any of the common manifestations of vitamin B12 deficiency, including glossitis, peripheral neuropathy, and gait abnormalities. Repeat blood smear showed severe leukopenia, macrocytic anemia, and 8% blasts. Extensive infectious workup was negative. Because blasts were seen on blood smear, a bone marrow biopsy was indicated. While awaiting biopsy results, there was continued discussion of whether the results would justify the diagnosis of leukemia or if severe vitamin B12 deficiency would obscure a true diagnosis. Bone marrow showed hypercellularity and 26-30% blasts with a myeloid phenotype expressing CD56, and after deliberation with the tumor board, he was diagnosed with acute myeloid leukemia (AML). He was initiated on a 10-day course of IV decitabine and is currently on venetoclax for thirty days.
Discussion: Pancytopenia is a decreased production of all three blood cell lines. Rather than a clinical diagnosis, it is a feature of an underlying pathology that is discovered on a CBC. When assessing a patient with pancytopenia, it is crucial to complete a thorough diagnostic workup. Initially, one should consider the presence of drugs or toxins, such as chemotherapeutics, NSAIDs, and alcohol misuse, as they are well-known causes of cell line depletion. Secondary workup should include reticulocyte count, blood smears, iron studies, inflammatory markers, liver function tests, and LDH. Further workup should be conducted to determine disorders of cell consumption, destruction, or production. These tests include vitamin B12, haptoglobin, infectious diseases, splenic ultrasound, etc. Destruction and production disorders then indicate bone marrow biopsy to rule-out malignant etiologies. (1)It is well-known that blood smear findings in the setting of vitamin B12 deficiency show megaloblastic anemia by disrupting RBC production. By the same mechanism, it can disrupt the production of WBCs and platelets, leading to pancytopenia. As previously stated, a bone marrow biopsy following abnormal blood smear results is needed to differentiate the etiologies of pancytopenia. According to ICC and WHO guidelines, AML is diagnosed on bone marrow biopsy using cytomorphology and immunophenotyping. (2,3) Cytomorphology shows hypercellularity with replacement of normal cells by leukemic blasts. Immunophenotyping shows different markers associated with myeloid lineages. There have been cases where vitamin B12 deficiency also shows hypercellularity and blastic differentiation within the bone marrow. (4) Due to these similarities, it can be difficult to differentiate between vitamin B12 deficiency and AML using bone marrow biopsy findings.
Conclusions: In conclusion, this patient had a bone marrow biopsy that showed hypercellularity and blasts, which can be associated with both vitamin B12 deficiency and AML. Ultimately, he had findings convincing enough for a diagnosis of AML; however, it is important to consider vitamin B12 deficiency in the differential, as it can share a similar presentation to acute leukemia.