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thrombocytosis (thrombocythemia)

Etiology: 1) myeloproliferative disorders a) essential thrombocythemia b) polycythemia vera c) chronic myelocytic leukemia d) myelofibrosis 2) secondary thrombocytosis a) recovery from acute infection b) malignancy - carcinoma - Hodgkin's disease - lymphoma c) hemolytic anemia d) postoperative - splenectomy - other surgical procedures e) acute & chronic hemorrhage f) iron deficiency g) pharmaceutical agents - epinephrine - vincristine h) chronic inflammatory disorders - rheumatoid arthritis - ulcerative colitis - hepatic cirrhosis - sarcoidosis - chronic infection [3] i) exercise j) stress k) recovery from myelosuppressive therapy l) therapy of vitamin B12 deficiency m) osteoporosis Epidemiology: - secondary thrombocytosis is more common than essential thrombocythemia - 20% of patients with essential thrombocythemia are < 40 years of age [2] Genetics: - associated with JAK2 V617F mutation - autosomal dominant form associated with defects in THPO Clinical manifestations: 1) essential thrombocytosis is associated with - arterial thrombosis - venous thrombosis - hemorrhage - splenomegaly 2) 2/3 of patients with essential thrombocytosis are asymptomatic 3) secondary thrombocytosis is NOT associated with thrombosis, hemorrhage, splenomegaly Laboratory: 1) complete blood count (CBC) sufficient if secondary thrombocytosis a) elevated platelet count (> 600,000/uL) b) platelet count can exceed 1E06/uL for primary or secondary thrombocytosis c) normal red cell volume (MCV) d) hemoglobin < 13 g/dL e) leukocyte count elevated in 1/2 of patients with essential thrombocythemia f) basophilia may be noted [2] 2) impaired platelet aggregation response to: a) epinephrine b) collagen c) adenosine diphosphate 3) comprehensive metabolic panel - hyperkalemia if platelets > 1E06/mm3 - lysis of platelets or leukocytes during clot formation & retraction - determine plasma K+ rather than serum K+ 4) bone marrow biopsy a) presence of adequate iron b) absence of collagen fibrosis c) absence of Philadelphia chromosome or other bcl-abl gene rearrangements 5) stem cell culture - spontaneous growth of megakaryocyte colony forming units in essential thrombocythemia 6) JAK2 V617F mutation (essential thrombocythemia) - JAK2 exon 12 mutation analysis 7) calreticulin gene mutation 8) MPL gene mutation Complications: 1) essential thrombocythemia associated with arterial thrombosis venous thrombosis, hemorrhage, splenomegaly 2) secondary thrombocytosis is NOT associated with thrombosis, hemorrhage, splenomegaly, or abnormal cytogenetic findings Management: 1) see essential thrombocythemia - hydroxyurea for high-risk essential thrombocythemia 2) secondary thrombocytosis: treat underlying disorder

Related

thrombocytopenia thrombophilia

Specific

essential thrombocythemia

General

platelet disorder; thromboasthenia

Database Correlations

OMIM 187950

References

  1. Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 1763
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 16, 17, 19. American College of Physicians, Philadelphia 1998, 2006, 2012, 2015, 2022
  3. Schiller G, in: UCLA Intensive Course in Geriatric Medicine & Board Review, Marina Del Ray, CA, Sept 12-15, 2001
  4. Geriatrics at your Fingertips, 13th edition, 2011 Reuben DB et al (eds) American Geriatric Society