In 2016, the WHO revised some of its myeloproliferative neoplasms to include the designation of pre-fibrotic primary myelofibrosis (pre-PMF), distinct from ET or the other MPNs. It was since found that most cases of pre-PMF were previously diagnosed as ET. Many criteria overlap in the two categories, including the JAK2 V617F mutation and the high platelet counts. One of the main differences is progression to myelofibrosis is only 0-1% in patients with true ET versus 10-12% in those with pre-PMF.
Other differences include the tendency for patients with pre-PMF to have lower hemoglobin and WBC counts (our patient had normal values) and more constitutional symptoms such as night sweats, fatigue, and weight loss (our patient had all three of these).
It has now been proposed that more patients have pre-PMF than ET. The major significance of this is that pre-PMF patients have a worse prognosis than true ET patients. The pre-PMF are more likely to evolve into other categories. The most significant difference in predicted life span is 14.7 - 21.8 years (depending on the age of diagnosis) for true ET compared to 10.5 - 14 years for pre-PMF.
The prevalence of ET has been estimated at 38-57 per 100,000 people.
