Platelet diseases

Thrombocytes, or blood platelets, play a key role in the processes of vascular-platelet hemostasis - the initial stage of thrombus formation.

Platelets are non-nuclear cellular elements of the blood, 1-4 µm in size (young forms of platelets are larger) and have a lifespan of 7-10 days. 1/3 of platelets are in the spleen and 2/3 in the bloodstream. The number of platelets in human peripheral blood varies between 150,000-400,000/mm ³. The average platelet volume is 7.1 femtoliters (1x10 ¹⁵ l).

When the number of platelets decreases or their function is impaired, bleeding may occur. The most typical bleeding is from damaged skin and mucous membranes: petechiae, purpura, ecchymosis, nasal, uterine, gastrointestinal bleeding, hematuria. Intracranial hemorrhages are quite rare.

The most common cause of thrombocytopenia is immune destruction of platelets under the influence of auto-, allo- or drug-induced antibodies.

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Pathophysiological classification of thrombocytopenic conditions

Increased destruction of platelets (with a normal or increased number of megakaryocytes in the bone marrow - megakaryocytic thrombocytopenia).

Immune thrombocytopenia

• Idiopathic:
  • ITP.
• ♦ Secondary:
  • induced by infections, including viral (HIV, cytomegalovirus [CMV], Epstein-Barr, herpes, rubella, measles, mumps, parvovirus B19) and bacterial (tuberculosis, typhoid);
  • drug-induced;
  • post-transfusion purpura;
  • autoimmune hemolytic anemia (Fischer-Evans syndrome).
  • systemic lupus erythematosus;
  • hyperthyroidism;
  • lymphoproliferative diseases;
  • allergy, anaphylaxis.
• Congenital immune thrombocytopenias:
  • congenital transimmune thrombocytopenia;
  • congenital alloimmune thrombocytopenia;
  • fetal erythroblastosis - Rh incompatibility.

Non-immune thrombocytopenia

• Caused by increased platelet consumption:
  • microangiopathic hemolytic anemia;
  • DIC syndrome;
  • chronic recurrent schizocytic hemolytic anemia;
  • hemolytic uremic syndrome;
  • TTP;
  • Kasabach-Merritt syndrome (giant hemangioma);
  • "blue" heart defects.
• Caused by increased platelet destruction:
  • medicinal (ristocetin, protamine sulfate, bleomycin, etc.);
  • aortic stenosis;
  • infections;
  • cardiac (artificial valves, repair of intracardiac defects, etc.);
  • malignant hypertension.

Disturbance of platelet distribution and deposition

• Hypersplenism (portal hypertension, Gaucher disease, congenital "blue" heart defects, neoplasms, infections, etc.)
• Hypothermia.

Decreased platelet production (decreased or absent megakaryocytes in the bone marrow - amegakaryocytic thrombocytopenia)

Hypoplasia or suppression of megakaryocytes 1

• Medicinal (chlorothiazides, estrogens, ethanol, tolbutamide, etc.).
• Constitutional:
  • thrombocytopenia in TAR syndrome (congenital absence of the radius bones);
  • congenital platelet hypoplasia without anomalies;
  • congenital hypoplastic thrombocytopenia with microcephaly;
  • rubella embryofetopathy;
  • trisomy 13.18;
  • Fanconi anemia.
• Ineffective thrombopoiesis:
  • megaloblastic anemia (deficiency of vitamin B ₁₂ and folic acid);
  • severe iron deficiency anemia;
  • hereditary thrombocytopenia;
  • paroxysmal nocturnal hemoglobinuria.
• Disorders of thrombocytopoiesis regulation:
  • thrombopoietin deficiency;
  • intermittent platelet dysgenesis;
  • cyclic thrombocytopenia.
• Metabolic disorders:
  • methylmalonic acidemia;
  • ketone glycinemia;
  • carboxyl synthetase deficiency;
  • isovaleric acidemia;
  • idiopathic hyperglycinemia;
  • newborns from mothers with hypothyroidism.
• Hereditary platelet disorders 2:
  • Bernard-Soulier syndrome;
  • May-Hegglin anomaly;
  • Wiskott-Aldrich syndrome;
  • sex-linked thrombocytopenia;
  • Mediterranean thrombocytopenia.
• Acquired aplastic diseases:
  • idiopathic;
  • drug-induced (overdose of antitumor drugs, organic and inorganic arsenic, mesantoin, trimetin, antithyroid, antidiabetic, antihistamine drugs, butadion, insecticides, gold preparations, idiosyncrasy to chloramphenicol);
  • radiation;
  • virus-induced (hepatitis, HIV, Epstein-Barr virus, etc.).

Infiltrative processes in the bone marrow

• Benign:
  • osteopetrosis;
  • storage diseases.
• Malignant:
  • neoplasms: leukemia, myelofibrosis, Langerhans cell histiocytosis.
  • secondary: lymphomas, neuroblastoma, metastases from solid tumors.

In case of decreased megakaryocyte count in bone marrow, in addition to aspiration, bone marrow biopsy is mandatory to prevent typical errors. These conditions are associated with normal or increased megakaryocyte count in bone marrow.