DIFFERENTIAL DIAGNOSIS
Dr. Edward J. Benz, Jr.: May we see the imaging studies?
Dr. Carol C. Wu: Posteroanterior (Figure 1AFIGURE 1
Imaging Studies.
) and lateral chest radiographs show mild enlargement of the cardiac silhouette and a paraspinal mass on the right, adjacent to the lower thoracic vertebral bodies. A CT scan of the chest (Figure 1B, 1C, and 1D) shows a smoothly marginated paraspinal mass on the right, measuring 5 cm (anteroposterior) by 3 cm (transverse) by 5 cm (craniocaudal), extending from the level of T9 to T11. A 1.2-cm soft-tissue mass adjacent to the right posterior eighth rib and a 1.0-cm mass adjacent to the left posterior ninth rib are also seen. Also, there is no evidence of cortical erosion of the vertebral bodies or ribs adjacent to these lesions. There is no evidence of intrathoracic lymphadenopathy. The paraspinal mass and the two paracostal lesions were isointense to the paraspinal muscle on T1-weighted and T2-weighted MRI before and after the administration of contrast material. There is no evidence of tumor widening or extension into the neural foramina or evidence of intralesional fat.
Infectious processes are unlikely, given the complete lack of involvement of adjacent bony structures and lack of inflammatory changes in the adjacent mediastinal fat. Two main differential considerations for a combination of paraspinal and paracostal masses include extramedullary hematopoiesis and multiple peripheral-nerve-sheath tumors. The paraspinal mass is taller than it is wide and is centered adjacent to the vertebral bodies rather than more posteriorly adjacent to the neural foramina; these features are atypical for peripheral-nerve-sheath tumors. The presence of intralesional fat on MRI would be supportive of extramedullary hematopoiesis, since fat is usually seen in the bone marrow, but its absence does not rule out the diagnosis. Clinical correlation with a history of anemia or neurofibromatosis would be helpful.
Dr. Benz: This patient presented with several striking findings: paraspinal masses, moderate anemia with profound microcytosis, splenomegaly, and recent onset of dyspnea and fatigue. It would be helpful to know whether these findings are long-standing or of recent onset, but we are hampered by the lack of a detailed medical history. Nevertheless, there is sufficient information to formulate a reasonable differential diagnosis. Certain chronic anemias that produce erythropoiesis with morphologic dysplasia (stress erythropoiesis) could also produce splenomegaly and masses of extramedullary hematopoiesis.1 Therefore, my approach will be to consider the most likely source of her anemia and whether this could be the source of the masses. I will then consider the relative likelihood of that cause versus others that should be considered in a 62-year-old woman.
Microcytic Anemia
What is most striking is the profound microcytosis in this patient who has only moderate anemia and a normal red-cell count. Microcytic anemias are due to defects in hemoglobin biosynthesis resulting from a reduced supply of iron (iron deficiency), inadequate delivery of iron (anemia of chronic inflammation), impaired production of heme (sideroblastic anemia), or defective synthesis of the globin component of hemoglobin (thalassemia) (Table 2TABLE 2
Differential Diagnosis of Hypochromic Microcytic Anemias.
).2 A mean corpuscular volume of 54 fl is so low that it effectively eliminates the possibility of anemia of chronic inflammation and sideroblastic anemia; in adults, these anemias almost never present with a mean corpuscular volume below 70 fl. Moreover, the mean corpuscular volume in iron deficiency rarely falls below 80 fl until the hematocrit is well below 30 and the red-cell count is less than 4 million. In contrast, a hallmark of thalassemia is a mean corpuscular volume that is disproportionately low for the degree of anemia. The Mentzer index (calculated as mean corpuscular volume ÷ red-cell count) is a quantitative expression of this phenomenon and was 8.92 in this patient.3 Microcytosis develops very late in iron deficiency, when hemoglobin synthesis is markedly impaired and the anemia is severe, whereas in thalassemia defective hemoglobin synthesis is present throughout life after the perinatal period. Further supporting the diagnosis of a thalassemia syndrome is this patient's Cambodian background. Gene frequencies for various forms of thalassemia are extraordinarily high in Southeast Asia (15 to 30%).4