Bone Marrow Cell Composition and Principles of Analysis

As indicated above, and as will be shown below, almost all disorders of the hematopoietic system can be diagnosed using clinical findings, blood analysis, and humoral data. There is no mystery about bone marrow diagnostics. The basic categories are summarized here to give an understanding of how specific diagnostic information is achieved; photomicrographs will show the appearance of specific diseases. Once the individual cell types, as given in the preceding pages, are recognized, it becomes possible to interpret the bone marrow smears that accompany the various diseases, and to follow further, analogous diagnostic steps. As a first step in the analysis of a bone marrow tissue smear or squash preparation, various areas in several preparations are broadly surveyed. This is followed by individual analysis of at least 200 cells from two representative areas. Table 4 shows the mean normal values and their wide ranges.

A combination of estimation and quantitative analysis is used, based on the following criteria:

Cell Density. This parameter is very susceptible to artifacts. Figure 18 shows roughly the normal cell density. A lower count may be due to the manner in which the sample was obtained or to the smearing procedure. A bone marrow smear typically shows areas where connective tissue adipocytes with large vacuoles predominate. Only if these adipocytes areas are present is it safe to assume that the smear contains bone marrow material and that an apparent deficit of bone marrow cells is real.

Increased cell density: e.g., in all strong regeneration or compensation processes, and in cases of leukemia and myeloproliferative syndromes (except osteomyelosclerosis).

Decreased cell density: e.g., in aplastic processes and myelofibrosis.

Table 4 Cell composition in the bone marrow: normal values (%)

Median

Median values and normal

values

range

(J. Boll)

(K. Rohr)

Red cell series

- Proerythrocytes

1

- Macroblasts (basophilic

3

3.5

0.5-7.5

erythroblasts)

- Normoblasts (poly-and

16

19

(7-40)

orthochromic erythro-

blasts)

Neutrophil series

- Myeloblasts

2.7

1

(0.5-5)

- Promyelocytes

9.5

3

(0-7.5)

- Myelocytes

14

15

(5-25)

- Metamyelocytes

10.5

15

(5-20)

- Band neutrophils

9.8

15

(5-25)

- Segmented neutrophils

17.5

7

(0.5-15)

Small cell series

- Eosinophilic granulocytes

5

3

(1-7)

- Basophilic granulocytes

1

0.5

(0-1)

- Monocytes

2

2

(0.5-3)

- Lymphocytes

6

7.5

(2.5-15)

- Plasma cells

1.5

1

(0.5-3)

Megakaryocytes

Cell densities vary widely, 0.5-2 per view

field during screening at low magni-

fication.

Ratios of Red Cell Series to White Cell Series. In the final analysis, bone marrow cytology allows a quantitative assessment only in relative terms.

The important ratio of red precursor cells to white cells is 1: 2 for men and 1: 3 for women.

Shifts towards erythropoiesis are seen in all regenerative anemias (hemorrhagic anemia, iron deficiency anemia, vitamin deficiency anemia, and hemolysis), pseudopolycythemia (Gaisböck syndrome), and poly-cythemia, also in rare pseudo-regenerative disorders, such as sideroach-restic anemia and myelodysplasias. Shifts toward granulopoiesis are seen in all reactive processes (infections, tumor defense) and in all malignant processes of the white cell series (chronic myeloid leukemia, acute leukoses).

Distribution and Cell Quality in Erythropoiesis. In erythropoiesis polychromatic erythroblasts normally predominate. Proerythroblasts and basophilic erythroblasts only make up a small portion (Table 4). Here, too, a left shift indicates an increase in immature cell types and a right shift an increase in orthochromatic erythroblasts. Qualitatively, vitamin B12 and folic acid deficiency lead to a typical loosening-up of the nuclear structure in proerythroblasts and to nuclear segmentation and break-up in the erythroblasts (megaloblastic erythropoiesis).

A left shift is seen in regenerative anemias except hemolysis. Atypical proerythroblasts predominate in megaloblastic anemia and erythremia.

A right shift is seen in hemolytic conditions (nests of normoblasts, ery-throns).

Distribution and Cell Quality in Granulopoiesis. The same principle is valid as for erythropoiesis: the more mature the cells, the greater proportion of the series they make up. A left shift indicates a greater than normal proportion of immature cells and a right shift a greater than normal proportion of mature cells (Table 4). Strong reactive conditions may lead to dissociations in the maturation process, e.g., the nucleus shows the structure of a myelocyte while the cytoplasm is still strongly basophilic. In malignancies, the picture is dominated by blasts, which may often be difficult to identify with any certainty.

A left shift is observed in all reactive processes and at the start of neo-plastic transformation (smoldering anemia, refractory anemia with excess blasts [RAEB]). In acute leukemias, undifferentiated and partially matured blasts may predominate. In agranulocytosis, promyelocytes are most abundant.

A right shift is diagnostically irrelevant.

Cytochemistry. To distinguish between reactive processes and chronic myeloid leukemia, leukocyte alkaline phosphatase is determined in fresh smears of blood. To distinguish between different types of acute leukemia, the peroxidase and esterase reactions are carried out (pp. 97 and 99), and iron staining is performed (p. 109) if myelodysplasia is suspected.

Cytogenetic Analysis. This procedure will take the diagnosis forward in cases of leukemia and some lymphadenomas. The fresh material must be heparinized before shipment, preferably after discussion with a specialist laboratory.

The bone marrow contains a mixture of all the hematopoietic cells

Mice Bone Marrow Smears

Fig. 18 Bone marrow cytology. a Bone marrow cytology of normal cell density in a young adult (smear from a bone marrow spicule shown at the lower right; magnification X100). b More adipocytes with large vacuoles are present in this bone marrow preparation with normal hematopoietic cell densities; usually found in older patients. c Normal bone marrow cytology (magnification X400). Even this overview shows clearly that erythropoiesis (dense, black, round nuclei) accounts for only about one-third of all the cells.

Fig. 18 Bone marrow cytology. a Bone marrow cytology of normal cell density in a young adult (smear from a bone marrow spicule shown at the lower right; magnification X100). b More adipocytes with large vacuoles are present in this bone marrow preparation with normal hematopoietic cell densities; usually found in older patients. c Normal bone marrow cytology (magnification X400). Even this overview shows clearly that erythropoiesis (dense, black, round nuclei) accounts for only about one-third of all the cells.

Qualitative and Quantitative Assessment of the Remaining Cells. Lymphocyte counts may be slightly raised in reactive processes, but a significant increase suggests a disease of the lymphatic system. The exact classification of these disease follows the criteria of lymphocyte morphology (Fig. 16). If elevated lymphocyte counts are found only in one preparation or within a circumscribed area, physiological lymph follicles in the bone marrow are likely to be the source. In a borderline case, the histology and analysis of lymphocyte surface markers yield more definitive data.

Plasma cell counts are also slightly elevated in reactive processes and very elevated in plasmacytoma. Reactive increase of lymphocytes and plasma cells with concomitant low counts in the other series is often an indication of panmyelopathy (aplastic anemia).

Raised eosinophil and monocyte counts in bone marrow have the same diagnostic significance as in blood (p. 44).

Megakaryocyte counts are reduced under the effects of all toxic stimuli on bone marrow. Counts increase after bleeding, in essential thrombocytopenia (Werlhof syndrome), and in myeloproliferative diseases (chronic myeloid leukemia, polycythemia, and essential thrombocythemia).

Iron Staining of Erythropoietic Cells. Perls' Prussian blue (also known as Perls' acid ferrocyanide reaction) shows the presence of ferritin in 20-40 % of all normoblasts, in the form of one to four small granules. The iron-containing cells are called sideroblasts. Greater numbers of ferritin granules in normoblasts indicate a disorder of iron utilization (side-roachresia, especially in myelodysplasia), particularly when the granules form a ring around the nucleus (ring sideroblasts). Perls' Prussian blue reaction also stains the diffuse iron precipitates in macrophages (Fig. 19 b).

Under exogenous iron deficiency conditions the proportion of sideroblasts and iron-storing macrophages is reduced. However, if the shift in iron utilization is due to infectious and/or toxic conditions, the iron content in normoblasts is reduced while the macrophages are loaded with iron to the point of saturation. In hemolytic conditions, the iron content of normoblasts is normal; it is elevated only in essential or symptomatic refractory anemia (including megaloblastic anemia).

Not just the individual cell, but its relative proportion is relevant in bone marrow diagnostics

Mice Bone Marrow Smears

Fig. 19 Normal bone marrow findings. a Normal bone marrow: megakaryocyte (1), erythroblasts (2), and myelocyte (3). b Iron staining in the bone marrow cytology: iron-storing macrophage. c Normal bone marrow with slight preponderance of granulocytopoiesis, e.g., promyelocyte (1), myelocyte (2), metamyelocyte (3), and band granulocyte (4). d Normal bone marrow with slight preponderance of erythropoiesis, e.g., basophilic erythroblast (1), polychromatic erythroblasts (2), and orthochromatic erythroblast (3). Compare (differential diagnosis) with the plasma cell (4) with its eccentric nucleus.

Fig. 19 Normal bone marrow findings. a Normal bone marrow: megakaryocyte (1), erythroblasts (2), and myelocyte (3). b Iron staining in the bone marrow cytology: iron-storing macrophage. c Normal bone marrow with slight preponderance of granulocytopoiesis, e.g., promyelocyte (1), myelocyte (2), metamyelocyte (3), and band granulocyte (4). d Normal bone marrow with slight preponderance of erythropoiesis, e.g., basophilic erythroblast (1), polychromatic erythroblasts (2), and orthochromatic erythroblast (3). Compare (differential diagnosis) with the plasma cell (4) with its eccentric nucleus.

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