Essential Thrombocythemia (ET) is a rare, chronic blood disorder characterized by the overproduction of platelets in the bone marrow. Platelets are tiny blood cells that play a crucial role in forming blood clots to stop bleeding. This condition is an acquired genetic disorder, meaning it develops due to gene changes that occur after birth.
The Numbers Behind Its Rarity
Essential Thrombocythemia is classified as a rare disease, with its prevalence and incidence rates highlighting its uncommon occurrence. Prevalence, the total number of existing cases, is estimated between 38 and 57 cases per 100,000 people. In the United States, prevalence is estimated at 1 in 4,200 individuals.
Incidence, the number of new cases diagnosed over a specific period, ranges from 0.2 to 2.5 new cases per 100,000 people per year. In the U.S., the annual incidence rate is approximately 1.5 per 100,000 persons.
What Essential Thrombocythemia Is
Essential Thrombocythemia is a type of myeloproliferative neoplasm (MPN), a group of blood cancers where the bone marrow produces too many blood cells. In ET, abnormal megakaryocytes, which are large cells in the bone marrow, produce an excessive number of platelets.
Platelets are cell fragments responsible for stopping bleeding by forming clots. When there are too many platelets, they can lead to abnormal blood clot formation, blocking blood vessels, or cause bleeding problems due to dysfunctional platelets. These complications can affect various parts of the body, potentially leading to serious events like heart attacks or strokes.
Identifying Essential Thrombocythemia
Many individuals with Essential Thrombocythemia do not experience symptoms, especially in the early stages, leading to an incidental diagnosis during routine blood tests. When symptoms do occur, they are often related to either blood clots or bleeding issues. Common symptoms can include fatigue, headaches, dizziness, blurred vision, or burning pain and redness in the hands and feet. Less frequently, bleeding problems such as easy bruising, nosebleeds, or gastrointestinal bleeding may manifest.
The diagnostic process typically begins with a complete blood count (CBC), which will reveal an elevated platelet count, usually above 450,000 per microliter. A peripheral blood smear allows for microscopic examination of blood cells to observe any abnormalities in platelet size or shape. To confirm the diagnosis and rule out other causes of high platelet counts, a bone marrow biopsy may be performed to examine the bone marrow for an increased number of megakaryocytes. Genetic testing for specific mutations, such as JAK2, CALR, or MPL, is also a routine part of the diagnostic workup.
Why Essential Thrombocythemia is Considered Rare
The rarity of Essential Thrombocythemia can be attributed to several factors, including the specific genetic mutations involved and the typical age of onset. The most common mutations associated with ET are JAK2 V617F, found in approximately 50% to 64% of patients, and mutations in the CALR gene, present in about 23% to 33% of cases. MPL gene mutations are less common, occurring in about 4% of patients.
ET is more frequently diagnosed in older adults, with the median age at diagnosis often ranging from 59 to 65 years. While it can occur at any age, including in younger individuals, especially women, the higher incidence in an older demographic naturally limits the overall number of cases compared to conditions that affect a broader age spectrum. The combination of specific, less common genetic mutations and an age-related prevalence pattern underpins why Essential Thrombocythemia remains a rare diagnosis.