164 Erythrocyte and Thrombocyte Abnormalities

Thrombocyte Abnormalities

EDTA in blood collection tubes (e.g., lavender top tubes) can lead to aggregation (pseudothrombocytopenia). A control using citrate as anticoagulant is required.

The clinical sign of spontaneous bleeding in small areas of the skin and mucous membranes (petechial bleeding), which on injury diffuses out to form medium-sized subcutaneous ecchymoses, is grounds for suspicion of thrombocyte (or vascular) anomalies.

Thrombocytopenia

Thrombocytopenias Due to Increased Demand (High Turnover)

A characteristic sign of this pathology can be that among the few thrombocytes seen in the blood smear, there is an increased presence of larger, i.e., less mature cell forms.

The bone marrow in these thrombocytopenias shows raised (or at least normal) megakaryocyte counts. Here too, there may be an increased presence of less mature forms with one or two nuclei (Figs. 60, 61).

Drug-induced immunothrombocytopenia As in drug-induced agranulocytosis, the process starts with an antibody response to a drug, or its metabolites, and binding of the antibody complex to thrombocytes. Rapid thrombocyte degradation by macrophages follows (Table 29). The most common triggers are analgesic/anti-inflammatory drugs and antibiotics.

Thrombocytes: increases, reductions, and anomalies may be seen

a

b

Fig. 59 Forms of thrombocytopenia. a This blood smear shows normal size and density of thrombocytes. b In this blood smear thrombocyte density is lower and size has increased, a feature typical of immunothrombocytopenia. continued !

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166 Erythrocyte and Thrombocyte Abnormalities

Table 29 Most common triggers of drug-induced immunothrombocytopenia

Analgesics	Quinine	Isoniazid
Antibiotics	Digitalis preparations	Methyldopa
Anticonvulsive drugs	Furosemide	Spironolactone
Arsenic, e. g., in water	Gold salts	Tolbutamide
Quinidine	Heparin!

“Idiopathic” immunothrombocytopenia. The name is largely historical, because often a trigger is found.

Postinfectious = acute form, usually occurs in children after rubella, mumps, or measles.

Essential thrombocytopenia, thrombocytopenic purpura (Werlhof disease)

Thrombocyte antibodies develop without an identifiable trigger. This is thus a primary autoimmune disease specifically targeting thrombocytes.

Secondary immunothrombocytopenias, e.g., in lupus erythematosus and other forms of immune vasculitis, lymphomas, and tuberculosis.

Post-transfusion purpura occurs mostly in women about one week after a blood transfusion, often after earlier transfusions or pregnancy.

Thrombocytopenia in microangiopathy. This group includes thrombotic– thrombocytopenic purpura (see p. 144) and disseminated intravascular coagulation.

Thrombocytopenia in hypersplenism of whatever etiology.

Fig. 59 Continued. c Pseudothrombocytopenia. The thrombocytes are not lying ! free and scattered around, but agglutinated together, leading to a reading of thrombocytopenia from the automated blood analyzer. d Giant thrombocyte (as large as an erythrocyte) in thrombocytopenia. Döhle-type bluish inclusion (arrow)

in the normally granulated segmented neutrophilic granulocyte: May-Hegglin anomaly.

Thrombocytes: increases, reductions, and anomalies may be seen

c d

e

Fig. 59 e Large thrombocyte (1) in thrombocytopenia. Thrombocyte-like fragments from destroyed granulocytes (cytoplasmic fragments) (2), which have the same structure and staining characteristics as the cytoplasm of band granulocytes

(3). Clinical status of sepsis with disseminated intravascular coagulation. In automated counters cytoplasmic fragments are included in the thrombocyte fraction.

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168 Erythrocyte and Thrombocyte Abnormalities

Thrombocytopenias Due to Reduced Cell Production

In this condition, blood contains few, usually small, pyknotic (“old”) thrombocytes. Only a very few megakaryocytes are found in the bone marrow, and these have a normal appearance.

Causes

Chronic alcoholism. There may be some overlap with increased turnover and folic acid deficiency.

Chemical and radiological noxae. Cytostatics naturally lead directly to a dose-dependent reduction in megakaryocyte counts. A large therapeutic radiation burden in the area of blood-producing bone marrow has the same result, which may persist for many months.

Virus infections. Measles, mononucleosis (Epstein–Barr virus, cytomegalovirus), rubella, and influenza may (usually in children) trigger thrombocytopenias of various types. In these cases, the virus affects the megakaryocytes directly. However, antibodies to thrombocytes may also arise in the course of these infections (p. 166), so that the pathomechanism of the parainfectious thrombocytopenias described by Werlhof in children may lie in impaired production and/or increased degradation of thrombocytes.

Neoplastic and aplastic bone marrow diseases. All neoplasms of the bone marrow cell series (e.g., leukemia, lymphoma, and plasmacytoma), together with their precursor forms (e.g., myelodysplasia), lead to progressive thrombocytopenia, as do panmyelophthisis and bone marrow infiltration by metastases from solid tumors.

Vitamin deficiency. Folic acid and vitamin B12 deficiencies from various causes (p. 152) also affect the rapidly proliferating megakaryocytes. In these cases, thrombocytopenia is often present before anemia and leukocytopenia in circulating blood, while the bone marrow shows copious megakaryocytes that have been blocked from maturation.

Constitutional diseases. An amegakaryocytic thrombocytopenia without any of the above causes is rare. It is seen in children with congenital radial aplasia; in adults it tends usually to be an early sign of leukemia, myelodysplastic syndrome, or aplastic anemia.

Wiscott-Aldrich syndrome (thrombocytopenia, immune deficiency, and eczema) is an X-chromosomal recessive disease in boys and presents with thrombocytopenia with ineffective megakaryopoiesis.

The May-Hegglin anomaly (dominant hereditary transmission) is characterized by thrombocytopenia with giant thrombocytes and granulocyte inclusions, which resemble Döhle bodies (endoplasmatic reticulum aggregates).

Variant forms of thrombocyte and megakaryocyte morphology in the bone marrow are diagnostic aids in thrombocytopenia

a	b
c	d
e	f

Fig. 60 Morphology of thrombocytes and megakaryocytes. a Bone marrow in thrombocytopenia due to increased turnover (e.g., immunothrombocytopenia). Mononuclear “young” megakaryocytes clearly budding a thrombocyte (irregular, cloudy cytoplasm structure). b In thrombocytopenia against a background of myelodysplasia, the bone marrow shows various megakaryocyte anomalies: here, too small a nucleus surrounded by too wide cytoplasm. c–f In myelodysplasia (c and d) and acute myeloid leukemia (e and f), bizarre anomalous thrombocyte shapes (arrows) may occasionally be found.

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170 Erythrocyte and Thrombocyte Abnormalities

Thrombocytosis (Including

Essential Thrombocythemia)

Reactive. Thrombocytosis in the form of a constant elevation of thrombocyte counts above an upper normal range of 300 000–450 000/µl, may be reactive, i.e., may appear in response to various tumors (particularly bronchial carcinoma), chronic inflammation (particularly ulcerative colitis, primary chronic polyarthritis), bleeding, or iron deficiency. The pathology of this form is not known.

Essential Thrombocythemia

Essential thrombocythemia, by contrast, is a myeloproliferative disease (see p. 114) in which the main feature of increased thrombocytes is accompanied by other signs of this group of diseases that may vary in severity, such as leukocytosis and an enlarged spleen. Severe thrombocythemia may also be seen in osteomyelosclerosis, polycythemia vera, and chronic myeloid leukemia, and for this reason the following specific diagnostic criteria have been suggested:

Diagnostic criteria for essential thrombocytopenia (according to Murphy et al.)

Thrombocytes !600 "109/l (with control)

Normal erythrocyte mass or Hb #18.5 g/dl !, 16.5 g/dl "

No significant bone marrow fibrosis

No splenomegaly

No leukoerythroblastic CBC

Absence of morphological or cytogenetic criteria of myelodysplasia

Secondary thrombocytosis (iron deficiency, inflammation, neoplasia, trauma, etc.) excluded

Large thrombocytes are found in the peripheral blood smear. However, these also occur in polycythemia vera and osteomyelosclerosis.

Bone marrow cytology will show markedly elevated megakaryocyte counts, with the cells often forming clusters and often with hypersegmented nuclei.

Fig. 61 Essential thrombocythemia. a Increased thrombocyte density and mar- ! ked anisocytosis in essential thrombocythemia. b Large thrombocytes (1) and a micro(mega)karyocyte nucleus (2) in essential thrombocythemia. Micro(mega)karyocytes are characterized by a small, very dense and often lobed nucleus with narrow, uneven cytoplasm, the processes of which correspond to thrombocytes (arrow).

		Thrombocyte proliferation with large megakaryocytes: essential
		thrombocythemia, a chronic myeloproliferative disease
a			b
c			d

Fig. 61 c and d Bone marrow cytology in essential thrombocythemia: there is a striking abundance of very large, hyperlobulated megakaryocytes (c); such megakaryocytes may also be seen in polycythemia vera. d Size comparison with basophilic erythroblasts (arrow). The cloudy cytoplasm of the megakaryocyte is typical of effective thrombocyte production.

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Cytology of Organ Biopsies

and Exudates*

*Special thanks to Dr. T. Binder, Wuppertal, for the generous gift of several preparations.