29th May 2023

Thrombocytosis

As with polycythaemia, thrombocytosis can be split into primary and secondary causes. Primary thrombocytosis can be associated with a number of haematological disorders, mostly myeloproliferative diseases. This includes PV, MF, CML, CMML and most commonly ET.

Essential thrombocytosis (ET)

This is the most common form of myeloproliferative neoplasm (MPN). Unlike PV, only platelet count is increased. Most patients present between 50-60 years.

It is associated with the following common mutations:

• JAK2 ~50%
• CALR ~30%
• MPL ~10%

The remainder of cases are classed as triple negative. If one of the above mutations is present, along with a platelet count over 450 x 10^9/L, this is sufficient to establish a diagnosis, providing there is no evidence of another MPN. Without one of the above three mutations, bone marrow investigation is usually necessary to confirm the diagnosis.

Features:

• Increased risk of venous and arterial thrombosis
• Increased risk of haemorrhage
• Constitutional symptoms
• Hepatosplenomegaly may be present
• Headache and dizziness
• Erythromelalgia
• Pregnancy complications

Prognosis

This is generally better than PV. Life expectancy is not affected for the first 10 years but is difficult to quantify afterwards. There is a risk of progression to MF and AML, but this is lower than in PV.

Treatment is similar to PV:

1. Manage CV risk factors
2. Aspirin for all patients
3. Cytoreductive patients only for high-risk patients (age >60, plt >1500, thrombotic or haemorrhagic complication)

Reactive thrombocytosis

There are a multitude of causes for this.

• Infection or inflammation/tissue damage
• Iron deficiency
• Hyposplenism
• Haemorrhage
• Drugs e.g. steroids
• Other malignancy e.g. sarcoma