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Vitamin B12 Deficiency 2

Vitamin B12 deficiency
pathology

Question

Vignette:

A 56-year-old female presents to the clinic with a 2-month history of worsening fatigue, generalized weakness, and recurrent infections. On examination, physical findings are notable for pallor, petechiae, and mild splenomegaly. Her complete blood count shows Hb: 8 g/dL, WBC: 3.5 x 10^9/L, and platelets: 70 x 10^9/L. Her peripheral blood smear is shown below:

[Image: Peripheral blood smear showing hypersegmented neutrophils]

Which of the following is the most likely diagnosis?

Choices

A. Acute myeloid leukemia

B. Iron deficiency anemia

C. Megaloblastic anemia

D. Myelofibrosis

E. Thalassemia

Answer

C. Megaloblastic anemia

Explanation

The patient's symptoms of fatigue, weakness, and recurrent infections, along with the laboratory findings of anemia, leukopenia, and thrombocytopenia, suggest a problem with the bone marrow. The presence of hypersegmented neutrophils on the peripheral blood smear is characteristic of megaloblastic anemia, which is usually due to a deficiency in vitamin B12 or folate.

Hypersegmented neutrophils are neutrophils with 6 or more lobes (normal is 2-5). The presence of these cells is a specific but not sensitive marker for megaloblastic anemia. Other causes of hypersegmented neutrophils include myelodysplastic syndromes and severe infections. However, these conditions are less likely in this patient given the other clinical and laboratory findings.

Acute myeloid leukemia (choice A) typically presents with similar symptoms and pancytopenia, but the peripheral blood smear would show blasts rather than hypersegmented neutrophils. Iron deficiency anemia (choice B) would cause microcytic anemia, not the macrocytic anemia seen in this patient. Myelofibrosis (choice D) could cause similar symptoms and pancytopenia, but the peripheral blood smear would show teardrop cells and poikilocytosis. Thalassemia (choice E) would cause microcytic anemia and is less likely in this patient without a family history or ethnic predisposition.

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