Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 28-year-old woman has a 3-month history of easy bruising and bleeding gums. She feels otherwise well. Medical and family histories are unremarkable, and she takes no medications.

On physical examination, temperature is normal, blood pressure is 110/70 mm Hg, pulse rate is 64/min, and respiration rate is 14/min. Petechiae are present on the buccal mucosa and pretibial areas, and ecchymoses are noted on the upper thighs. There is no lymphadenopathy or splenomegaly.

Laboratory studies:

Hemoglobin	10.4 g/dL (104 g/L)
Leukocyte count	5200/µL (5.2 × 109/L)
Absolute neutrophil count	1200/µL (1.2 × 109/L) (normal >1500/µL [1.5 × 109/L])
Platelet count	18,000/µL (18 × 109/L)
Reticulocyte count	0.9% of erythrocytes
Direct antiglobulin (Coombs) test	Negative

A peripheral blood smear shows no circulating blasts. The platelets are decreased and are not clumped, enlarged, or bizarre in appearance. Bone marrow examination shows hypoplastic marrow (<20% cellularity) with trilineage normoblastic maturation and normal iron stores. There are no findings suggesting an infiltrative disease and no increases in CD34 blasts or reticulin fibrosis.

Which of the following is the most likely diagnosis?

A) Acute myeloid leukemia
B) Aplastic anemia
C) Immune thrombocytopenic purpura
D) Myelodysplastic syndrome

Answer and critique

The correct answer is B) Aplastic anemia. This item is available to MKSAP 15 subscribers as item 46 in the Hematology and Oncology section.

This patient has aplastic anemia. Patients with this disorder have pancytopenia and a hypoplastic bone marrow (<20 cellularity) with normal maturation of all cell lines. Aplastic anemia is a fatal disorder in which myeloid progenitor cells and stem cells are severely diminished or absent in the bone marrow because of an intrinsic defect of the stem cells or immune-mediated stem cell destruction, which leads to transfusion-dependent anemia, thrombocytopenia, and severe neutropenia. In approximately 50% of cases of aplastic anemia, there is no obvious cause, whereas chemicals, drugs, viral infections, collagen vascular diseases, and thymoma can be implicated in the remaining cases. Interferon-activated T lymphocytes are implicated in autoimmune destruction of stem cells in a significant proportion of patients with the idiopathic or the acquired form of the disease; this fact explains why immunosuppressive therapy is effective in some patients. Initial management involves withdrawal of any potentially causative agents and a CT scan of the chest to rule out an associated thymoma.

Patients with acute myeloid leukemia may have pancytopenia, but bone marrow examination shows infiltration with CD34 blasts, and circulating myeloblasts are likely to be present on the peripheral blood smear.

Patients with immune thrombocytopenic purpura (ITP) have petechiae and ecchymoses but do not have a decreased leukocyte count. Although patients with ITP and an associated autoimmune hemolytic anemia may have a low hemoglobin level, this patient’s direct antiglobulin (Coombs) test was negative, and she had a low reticulocyte count. In addition, her bone marrow did not show the increased number of megakaryocytes characteristic of ITP. Finally, some patients with ITP may have anemia secondary to bleeding; however, this patient does not have a clinical history of bleeding, and her iron stores are normal, suggesting that hemorrhage is not the cause of her anemia.

Although pancytopenia may be present in patients with a myelodysplastic syndrome, bone marrow examination typically shows hypercellular marrow. In addition, the diagnosis of a myelodysplastic syndrome requires the presence of dysplasia in at least two cell lines, which is not present in this patient.

Key Point

• Patients with aplastic anemia have pancytopenia, a low reticulocyte count, and hypoplastic bone marrow.

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