Canadian Association of Pathologists - Case of the Month - October, 2007

Diagnosis:

Parvovirus infection of bone marrow.

Microscopic Description:

Both the marrow aspirate smear and biopsy specimens are remarkable for the almost complete absence of mature erythroid precursors. Close inspection of the aspirate smear (see arrows in central area of annotated aspirate smear) reveals giant atypical pronormoblasts with nuclear inclusions. Similarily, the biopsy shows, in addition to the dramatic decrease in mature erythrooiesis, atypical giant early hematopoietic precursors with unusual clear or 'ground glass' type nuclear inclusions representing pronormoblasts infected with Parvovirus. Immunohistochemistry on the biopsy shows the atypical giant cells are erythroid precursors staining positively for Hemoglobin A1. Parvovirus infection is included in the differential diagnosis of pure red cell aplasia.

Pure red cell aplasia:

In this disorder a normocytic anemia occurs with diminished reticulocytes (<1%), absence of polychromasia on the peripheral blood smear, and almost no erythroblasts in the bone marrow (<0.5% of the marrow differential count), despite normal megakaryocytes and white cell precursors. It may develop without apparent cause or be associated with a wide variety of systemic diseases. It occurs in about 5% of patients with thymoma, and this tumor accounts for approximately 10% of cases of pure red cell aplasia. Hematologic malignancies, especially chronic lymphocytic and large granular lymphocytic leukemias, have been associated, as have some solid tumors, rheumatic diseases (such as Sjogren's syndrome and systemic lupus erythematosus), and infections, primarily parvovirus B19. Numerous medications have been implicated, including phenytoin, azathioprine, and isoniazid. Sometimes, pure red cell aplasia occurs during pregnancy without any apparent explanation and typically disappears following delivery. In many patients no cause is found. Often in these cases, an IgG that inhibits erythropoiesis is present in the serum.

Key Fields of view in this case:

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Annotated Digital Slides:

Bone Marrow Aspirate Smear
Bone Marrow Biopsy

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