From the Guidelines
Thrombocytosis is primarily caused by either primary thrombocytosis, also known as essential thrombocythemia, which is due to genetic mutations in bone marrow stem cells, or secondary thrombocytosis, which occurs as a reaction to underlying conditions such as inflammation, infections, iron deficiency anemia, and malignancies. The most recent and highest quality study on this topic is from 2021 1, which discusses the thrombotic risk in myeloproliferative neoplasms, including essential thrombocythemia. According to this study, primary thrombocytosis is associated with an increased risk of thrombotic events, particularly arterial thrombosis. Some common causes of secondary thrombocytosis include:
- Acute or chronic inflammation
- Infections
- Iron deficiency anemia
- Tissue damage
- Malignancies, such as lung, gastrointestinal, breast, and lymphoma
- Post-splenectomy state
- Certain medications, like epinephrine, vincristine, and all-trans retinoic acid Inflammatory conditions, such as rheumatoid arthritis, inflammatory bowel disease, and connective tissue disorders, can also trigger thrombocytosis through increased production of thrombopoietin and inflammatory cytokines like IL-6 1. It's worth noting that the presence of a condition associated with reactive thrombocytosis does not exclude the possibility of essential thrombocythemia if other criteria are met, as stated in the 2008 revision of the World Health Organization classification of myeloid neoplasms and acute leukemia 1. In clinical practice, it's essential to distinguish between primary and secondary thrombocytosis, as the management and treatment of these conditions differ significantly, with primary thrombocytosis requiring specific hematologic management to prevent thrombotic complications.
From the Research
Causes of Thrombocytosis
Thrombocytosis, or elevated platelet count, can be caused by various factors, including:
- Myeloproliferative neoplasms, such as essential thrombocythemia, polycythemia vera, primary myelofibrosis, and chronic myeloid leukemia 2, 3, 4, 5
- Inflammatory conditions, such as rheumatoid arthritis and systemic lupus erythematosus 2
- Infections 2
- Splenectomy 2
- Iron deficiency anemia 2
- Solid tumors, such as lung cancer 2
- Genetic variants that upregulate the JAK-STAT signaling pathway, including Janus kinase 2 (JAK2), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL) 2, 3, 4, 5
- Other mutations, such as TET2, ASXL1, DNMT3A, and SF3B1 3
Disease Characteristics
Essential thrombocythemia is characterized by:
- A persistent platelet count of 450 × 10^9/L or greater 2
- An increased risk of thrombosis and bleeding 2, 3, 4, 5
- A median age at diagnosis of 59 years 2
- A median overall survival of more than 35 years in those diagnosed at 40 years or younger 2
- A risk of transformation into myelofibrosis or acute myeloid leukemia 2, 3, 4, 5
Risk Factors
Risk factors for thrombosis in essential thrombocythemia include: