1.1.4 Differential Diagnosis

1.1.4 Differential Diagnosis

Aplastic anemia must be differentiated from the following diseases:

First, Paroxysmal Nocturnal Hemoglobinuria (PNH): Although some PNH patients also exhibit pancytopenia and may occasionally experience bone marrow hypoproliferation, making it easy to confuse with aplastic anemia, PNH typically presents with mild jaundice, slightly elevated reticulocyte counts, and positive results in acidified serum hemolysis test (Ham test), sugar water test, and urine ferritin test, whereas aplastic anemia tests negative. Red blood cells show markedly reduced cholinesterase activity, and neutrophils often exhibit significantly reduced alkaline phosphatase activity—features that distinguish PNH from aplastic anemia. Occasionally, aplastic anemia and paroxysmal nocturnal hemoglobinuria coexist or transform into each other.

Second, Bone Marrow Fibrosis: During bone marrow aspiration, this condition often yields only a small amount of blood rather than actual bone marrow tissue, and the smear contains very few cells, easily leading to misdiagnosis as aplastic anemia. However, blood smears frequently reveal numerous red blood cells of diverse shapes, such as teardrop-shaped cells, oval-shaped cells, and fragmented cells, along with nucleated cells and immature granulocytes; white blood cell counts are often elevated; the liver and spleen are markedly enlarged; and bone marrow biopsy shows extensive proliferation of fibrous tissue in the marrow—features absent in aplastic anemia.

Third, Acute Leukemia: Often presents with anemia, bleeding, and fever, with frequent hepatosplenomegaly; hematological findings show pancytopenia, and bone marrow morphology indicates hypoproliferation, easily confused with aplastic anemia. However, low-proliferation, low-percentage leukemia may exhibit immature cells in the blood, with the bone marrow filled with blast or immature cells, whereas aplastic anemia cases rarely show an increase in blast cells.

Fourth, Pre-leukemic State: Also characterized by pancytopenia, with many blood cells exhibiting abnormal morphologies, such as uneven red blood cell sizes, large oval-shaped red cells, and nucleated red cells. Commonly seen are a few immature granulocytes and typical single-nucleated granulocytes, along with abnormal platelet shapes; bone marrow examination reveals that pre-leukemic patients have active bone marrow proliferation, with no increase in leukemic blasts, but moderate to severe increases in intermediate and mature single-nucleated cells, as well as possible megaloblastic changes in young red cells. Megakaryocytes are mostly unchanged, which helps differentiate from aplastic anemia.

Fifth, Malignant Histiocytosis: Also presents with pancytopenia, but often accompanied by high fever that cannot be explained by infection, severe bleeding, hepatosplenomegaly, and lymph node enlargement. Bone marrow examination reveals abnormal histiocytes, distinguishing it from aplastic anemia.

Sixth, Myelodysplastic Syndrome (MDS): Also characterized by pancytopenia and chronic anemic symptoms, easily confused with aplastic anemia. Abnormal hematopoiesis can be observed across all three lineages—granulocyte, red blood cell, and megakaryocyte:

• Granulocyte Lineage: Excessive nuclear lobulation, abnormal nuclei, double-nucleated immature granulocytes, giant late-stage granulocytes, abnormal blast and early-stage granulocytes, irregular or diminished granule distribution, negative peroxidase staining, and reduced alkaline phosphatase activity.
• Red Blood Cell Lineage: Disrupted nuclear-cytoplasmic maturation, abnormal nuclei, multiple nuclei, nuclear rupture, and ring-shaped iron-rich granulocytes accounting for more than 20% of young red cells.
• Megakaryocyte Lineage: Presence of small megakaryocytes, excessive nuclear lobulation in megakaryocytes, and giant platelets.

MDS patients often exhibit active or markedly active bone marrow proliferation; in some cases, the bone marrow contains an increase in blast and early-stage cells, with enhanced red blood cell production, inverted granulocyte-to-red-cell ratio, and relatively stable megakaryocyte numbers. Peripheral blood sometimes shows increased platelet counts and a higher proportion of single-nucleated cells, with frequent nucleated red cells.

In addition, other diseases that can cause pancytopenia include bone marrow metastases, bone marrow sclerosis, marble disease, multiple myeloma, malignant lymphoma, systemic fungal infections, severe sepsis, and nutritional deficiencies. Each of these conditions has distinctive features, making them relatively easy to differentiate from aplastic anemia.