Infectious Processes in Blood and Bone Marrow

Viral Infections

Certain viral infections can cause cytopathic changes in blood cells or changes in the maturation of blood cells. The nuclear or cytoplasmic inclusions of some viruses, particularly the herpesviruses, are visible by light microscopy. The most easily identified cytopathic changes are those of cytomegalovirus (CMV) ( Fig. 17.1 ). Nonspecific findings in bone marrow of CMV-infected patients may include myeloid and megakaryocytic suppression, hemophagocytosis, granulomas, or lymphoid aggregates; atypical lymphocytosis similar to that seen in infectious mononucleosis may be seen in peripheral blood. Circulating CMV-infected endothelial cells may sometimes be present at the feathered edge of a peripheral smear. Primary Epstein-Barr virus (EBV) infection causes large atypical lymphocytes in peripheral blood that are the origin of the term “infectious mononucleosis.” The bone marrow of EBV-infected patients may show focal lymphocytosis or fibrin ring granulomas. Human parvovirus B19 replicates in late erythroid precursor cells in bone marrow, resulting in giant pronormoblasts ( Figs. 17.2–17.4 ). An occasional pronormoblast may contain an eosinophilic inclusion that displaces the nuclear chromatin to the periphery and may contain cytoplasmic vacuoles. Early in human immunodeficiency (HIV) infection, the bone marrow may be hypercellular but becomes hypocellular in advanced disease and following therapy. Other findings in HIV-infected patients may include increased plasma cells, scattered macrophages, dysplastic hematopoietic cells, fibrosis, lymphoid hyperplasia, or proliferation of immunoblasts. The peripheral blood findings of paroxysmal cold hemagglutination (red blood cell agglutination and erythrophagocytosis by neutrophils) may be seen in a variety of viral (e.g., varicella, measles, mumps, and upper respiratory) and bacterial (e.g., syphilis and Haemophilus influenzae ) infections.