Published: 18 Jun 2025

ICD9: 238.71      ICD10: D47.3      ICD11: 3B63.1Z

Essential thrombocytosis (ET), also known as primary thrombocythemia, is a rare, chronic blood disorder characterized by the overproduction of platelets by the bone marrow.
Platelets, also known as thrombocytes, are essential for blood clotting. This overproduction can lead to a variety of complications, primarily related to blood clots and, paradoxically, bleeding.

Here's a more detailed breakdown:

Key Features:

Overproduction of Platelets: The bone marrow, specifically the megakaryocytes (cells that produce platelets), becomes hyperactive and produces an excessive number of platelets. The platelet count is typically significantly elevated, often exceeding 450,000 per microliter of blood, and sometimes reaching over 1,000,000.
Chronic Myeloproliferative Neoplasm (MPN): ET is classified as a chronic myeloproliferative neoplasm. This means it's a type of cancer that affects the blood-forming cells in the bone marrow. However, it's generally a slower-growing and less aggressive cancer than some others.
JAK2, CALR, or MPL Mutations: A significant percentage of ET patients have mutations in genes that regulate blood cell production, most commonly the *JAK2*, *CALR*, or *MPL* genes. These mutations contribute to the uncontrolled growth of megakaryocytes. However, a significant portion of ET patients do not have any identifiable mutation (called "triple negative").
Differentiation from Reactive Thrombocytosis: It's crucial to distinguish ET from reactive thrombocytosis, which is an elevated platelet count caused by another underlying condition, such as infection, inflammation, iron deficiency, or recent surgery. Reactive thrombocytosis is a secondary condition, and the platelet count usually returns to normal once the underlying cause is treated. ET, in contrast, is a primary disorder of the bone marrow.

Symptoms:

Many people with ET have no symptoms, especially in the early stages. When symptoms do occur, they can vary widely and include:

Blood Clots (Thrombosis): The increased number of platelets can lead to the formation of blood clots in various parts of the body, potentially causing:
Stroke: Clots in the brain.
Heart Attack: Clots in the heart.
Deep Vein Thrombosis (DVT): Clots in the legs.
Pulmonary Embolism (PE): Clots in the lungs.
Splenic Vein Thrombosis: Clots in the vein leading from the spleen.
Erythromelalgia: Burning pain and redness in the hands and feet, often triggered by warmth or exercise. This is caused by small vessel blood clots.
Bleeding (Paradoxical): Despite the high platelet count, some people with ET experience bleeding problems. This occurs because the platelets, while numerous, may not function properly. Bleeding can manifest as:
Nosebleeds: Frequent or heavy nosebleeds.
Easy Bruising: Bruising easily.
Gastrointestinal Bleeding: Bleeding in the stomach or intestines.
Prolonged Bleeding After Minor Cuts: Cuts that take longer than usual to stop bleeding.
Other Symptoms:
Headaches: Can be severe and persistent.
Dizziness: Feeling lightheaded or unsteady.
Fatigue: Feeling unusually tired or weak.
Visual Disturbances: Blurred vision or temporary loss of vision.
Enlarged Spleen (Splenomegaly): May cause abdominal discomfort or a feeling of fullness.

Diagnosis:

Diagnosis typically involves:

Complete Blood Count (CBC): Shows an elevated platelet count.
Peripheral Blood Smear: Examination of blood cells under a microscope to look for abnormalities.
Bone Marrow Biopsy and Aspirate: The most definitive diagnostic test. It helps to rule out other causes of thrombocytosis and assess the megakaryocytes in the bone marrow.
Genetic Testing: To detect mutations in the *JAK2*, *CALR*, and *MPL* genes.
Ruling Out Reactive Thrombocytosis: Investigating for underlying conditions that could be causing a secondary increase in platelet count.

Treatment:

The goal of treatment is to reduce the risk of blood clots and bleeding. Treatment options depend on the patient's risk factors for these complications and may include:

Low-Dose Aspirin: To help prevent blood clots.
Cytoreductive Therapy: Medications to lower the platelet count. Common medications include:
Hydroxyurea: A chemotherapy drug that reduces platelet production.
Anagrelide: A drug that specifically reduces platelet production.
Interferon alfa: Another drug that can lower the platelet count, often used in younger patients or pregnant women.
Phlebotomy: Removing blood from the body to lower the blood cell count (rarely used anymore).
Monitoring: Regular blood tests and monitoring for signs of complications.

Prognosis:

The prognosis for ET is generally good, especially with appropriate treatment and monitoring. Most people with ET have a normal life expectancy. However, there is a small risk of transformation to more aggressive myeloproliferative neoplasms like myelofibrosis or acute leukemia. The risk of these transformations is relatively low, but it's essential to be aware of it.

Important Considerations:

Individualized Treatment: Treatment decisions are highly individualized and depend on a patient's specific risk factors, symptoms, and overall health.
Close Monitoring: Regular follow-up with a hematologist (blood specialist) is crucial for monitoring the disease and adjusting treatment as needed.
Patient Education: Understanding the condition, its potential complications, and the importance of adhering to treatment plans is essential for managing ET effectively.
Pregnancy: Pregnancy in women with ET requires careful management to minimize the risk of complications for both the mother and the baby.

In summary, essential thrombocytosis is a chronic blood disorder characterized by the overproduction of platelets. While often asymptomatic, it can lead to serious complications related to blood clots or bleeding. Diagnosis involves blood tests and bone marrow examination, and treatment aims to reduce the risk of these complications through medication and lifestyle management. The prognosis is generally good with appropriate care and monitoring.

Disclaimer: This information is for general knowledge and educational purposes only, and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.