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  • Classification is difficult because few diseases result solely in disturbance of monocytes.

  • Presence of monocytosis, monocytopenia, or histiocytosis may be an important diagnostic feature and may contribute to functional abnormalities.

  • The terms macrophage and histiocyte are synonymous.

    — Macrophage is the correct designation when discussing tissue disorders of the mononuclear phagocyte system.

    — The latter system is the sum of the marrow, blood, and tissue pool of monocytes and macrophages. (The term reticuloendothelial for this system is obsolete.)

    — For historical reasons, macrophage disorders are referred to by pathologists as a histiocytic disorder or a histiocytosis (eg, Langerhans cell histiocytosis).

Table 34–1 provides a comprehensive array of disorders of monocytes, macrophages, and (myeloid) dendritic cells. Chapter 35 discusses the various causes for increases and decreases in blood monocytes. Chapters 36 and 37 discuss the principal histiocytic disorders.


image For a more detailed discussion, see Marshall A. Lichtman: Classification and Clinical Manifestations of Monocytes and Macrophages, Chap. 69 in Williams Hematology, 10th ed.

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