Chapter 2 Aplastic Anemia
PATHOPHYSIOLOGY
Aplastic anemia occurs when bone marrow failure leads to the depletion of all marrow elements. The production of blood cells is decreased or lacking. Pancytopenia and hypocellularity of the marrow occur. The manifestation of symptoms is dependent on the extent of the thrombocytopenia (hemorrhagic symptoms), neutropenia (bacterial infections, fever), and anemia (pallor, fatigue, congestive heart failure, tachycardia). Severe aplastic anemia is characterized by a granulocyte count of less than 500/mm3, a platelet count of less than 20,000/mm3, and a reticulocyte count of less than 1%. Aplastic anemia can be acquired or inherited. Acquired forms can be caused by drugs (chloramphenicol and chemotherapeutic agents), chemicals (benzene), radiation, or viral infection (hepatitis virus, human parvovirus, Epstein-Barr virus), and in rare instances are associated with paroxysmal nocturnal hemoglobinuria. Fanconi’s anemia is the most common inherited type and is associated with various physical findings and renal and cardiac abnormalities. Diamond-Blackfan anemia is a hypoplastic anemia that only affects the erythrocyte cell line; it is diagnosed in early infancy.
INCIDENCE
1. About 100 new cases of acquired aplastic anemia are diagnosed each year in children in the United States.
2. Aplastic anemia may occur at any age.
3. The majority of cases are idiopathic.
4. Long-term survival rate with bone marrow transplant from histocompatible donors is as high as 75% to 95% in children. Without bone marrow transplant, survival is about 50%.
5. Males and females are affected equally with Fanconi’s anemia. Most cases are diagnosed at about 7 years of age, although the disorder may be diagnosed in infancy or as late as 30 to 40 years of age.
CLINICAL MANIFESTATIONS
1. Petechiae, ecchymoses, epistaxis (occur first as a result of low platelet counts)
2. Oral ulcerations, bacterial infections, fever (occur later in course)
3. Anemia, pallor, fatigue, tachycardia (late signs)
4. Café-au-lait spots, melanin-like hyperpigmentation, absent thumbs, renal abnormalities, short stature (Fanconi’s anemia)
5. Pallor and anemia at birth or in early infancy (Diamond-Blackfan anemia)
COMPLICATIONS
LABORATORY AND DIAGNOSTIC TESTS
1. Bone marrow aspiration and biopsy—used to assess the cells in the bone marrow; findings are marrow hypoplasia with less than 25% normal cellularity.
2. Complete blood count with differential—used to evaluate circulating numbers and sizes of red and white blood cells. Findings with aplastic anemia include macrocytic anemia and decreased absolute neutrophil count to less than 500/μL. White blood cell counts are normal in Diamond-Blackfan anemia.
3. Platelet count—used to assess the number of platelets in the blood, which are needed for blood clotting. Findings include a platelet count of less than 20,000/μL. Platelet counts are normal in Diamond-Blackfan anemia.
4. Reticulocyte count—used to indirectly analyze hematopoiesis or the forming and development of blood cell lines. Decreased reticulocyte count in the presence of anemia indicates underlying pathology.
5. Hemoglobin electrophoresis—used to detect presence of fetal hemoglobin, which is increased in Diamond-Blackfan anemia.
