Polycythemia is a blood disorder characterized by an abnormally high number of red blood cells. The age of onset varies significantly depending on the type of polycythemia, which is broadly classified as either primary (caused by an intrinsic bone marrow problem) or secondary (caused by another medical condition or external factor).
Age of onset for polycythemia vera (Primary polycythemia)
Polycythemia vera (PV) is the most well-known form of primary polycythemia. It is a rare, slow-growing blood cancer that results from a genetic mutation in the bone marrow's blood-forming cells.
- Median age at diagnosis: For PV, the median age at diagnosis is typically around 60 years old.
- Higher incidence in older adults: The risk of developing PV increases with age, with most cases occurring in people over 60. Men are also slightly more likely to be affected than women.
- Rare in younger populations: Though rare, PV can affect individuals of any age. Cases have been reported in children and young adults, but less than 10% of cases occur in people under 40. The onset can be in early adulthood and occasionally in children and adolescents, but this is uncommon.
Age of onset for secondary polycythemia
Secondary polycythemia occurs when another medical condition or external factor causes the body to produce too many red blood cells. The age of onset for this type is entirely dependent on the underlying cause.
- Chronic lung or heart disease: Conditions like severe chronic obstructive pulmonary disease (COPD) or congenital heart disease can lead to secondary polycythemia. In these cases, polycythemia develops alongside or as a result of the primary condition, which can occur at various ages. For example, studies have shown that patients with secondary polycythemia due to such conditions have a median age of diagnosis around 63 years, though it is not exclusive to older age.
- Environmental factors: Living at high altitudes, where oxygen levels are lower, can cause secondary polycythemia as the body compensates by producing more red blood cells. This can affect individuals of any age who move to or live in these areas. Similarly, heavy smoking can also cause chronically low oxygen levels, leading to polycythemia.
- Neonatal polycythemia: A specific type of secondary polycythemia can occur in newborns and is detected before or at birth. This can be caused by delayed umbilical cord clamping, twin-twin transfusion syndrome, or a diabetic birth mother.
Congenital and familial polycythemia
Some forms of polycythemia are hereditary, meaning they are caused by genetic mutations present from birth. These are a type of primary polycythemia but are distinct from polycythemia vera.
- Early onset: Unlike PV, these inherited conditions can manifest in childhood or early adulthood.
- Specific genetic causes: Examples include Primary Familial and Congenital Polycythemia (PFCP), caused by mutations in the erythropoietin receptor gene, and Chuvash polycythemia, caused by a mutation in the VHL gene. The age of onset for these can be quite young, and in some cases, symptoms may not appear until later in life despite the genetic predisposition.
Comparison of polycythemia types by age of onset and cause
| Feature | Polycythemia Vera (Primary) | Secondary Polycythemia | Congenital/Familial Polycythemia |
|---|---|---|---|
| Median Age of Diagnosis | Around 60 years old | Variable, often alongside an underlying condition, such as around 63 years for COPD patients | Varies from childhood to adulthood, depending on the specific genetic mutation |
| Rare Age Occurrences | Rare cases in children and young adults under 40 | Neonatal cases are a specific subtype | Onset can range from early childhood to adulthood |
| Underlying Cause | Acquired genetic mutation (e.g., JAK2) in bone marrow stem cells | Response to an external factor causing tissue hypoxia (e.g., lung disease, high altitude, smoking) or an erythropoietin-secreting tumor | Inherited genetic mutation affecting red cell production (e.g., EPOR or VHL gene mutations) |
Symptoms and complications related to age
The symptoms and risks associated with polycythemia can also differ depending on the age of onset.
Adults with Polycythemia Vera:
- Risk of blood clots: Age is a major risk factor for thrombosis (blood clots) in patients with PV. Adults over 60 are considered high-risk, alongside those with a history of thrombosis. Blood clots can lead to serious complications like heart attacks or strokes.
- Symptom progression: Since PV is slow-growing, many adults, especially those over 60, are diagnosed incidentally during routine blood work. Other symptoms often appear gradually over time and can include headaches, dizziness, itchy skin, and an enlarged spleen.
Children with Polycythemia:
- Pediatric risks: For children with polycythemia, risks can include developmental issues and, in some cases, severe bleeding or thrombotic events. Congenital forms can be associated with an increased risk of vascular problems later in life.
- Budd–Chiari syndrome: This rare but serious complication, involving blood clots in the liver veins, has been reported in younger patients with polycythemia.
Conclusion
The age at which polycythemia occurs is not a single value but depends on the specific type of the condition. While polycythemia vera is most commonly a disease of older adulthood, with a median age of diagnosis around 60, other forms exist across the entire lifespan. Congenital and familial polycythemia can manifest in childhood, and secondary polycythemia can appear at any age depending on the triggering factor, such as lung disease or high altitude exposure. This highlights the importance of a proper medical diagnosis to determine the underlying cause and ensure appropriate management for any patient presenting with elevated red blood cell counts, regardless of their age.
For more in-depth information on blood cancers like polycythemia vera, refer to the Leukemia & Lymphoma Society.
