Several biological factors contribute to spleen enlargement in polycythemia vera:

1. Overproduction of blood cells: The spleen helps remove older or damaged red blood cells. In PV, the increased number of cells forces it to work harder, causing it to expand.
2. Bone marrow stress or scarring: When the bone marrow becomes scarred (fibrosis), it cannot make blood effectively, so the spleen begins producing blood cells instead (the spleen starts making blood cells itself) [3].
3. Inflammatory and vascular growth factors: Substances such as vascular endothelial growth factor (VEGF), a natural chemical that helps the growth of new blood vessels and may contribute to spleen enlargement [4].

Splenomegaly is one of the physical findings in PV. Newer imaging-based studies have shown spleen enlargement, even when it can’t be felt by touch. [5].

Notably, one study found that spleen size at diagnosis can predict future outcomes; patients with larger spleens tended to have a higher risk of developing bone marrow scarring after PV and a shorter survival compared to those without splenomegaly [2].

An enlarged spleen can cause a variety of symptoms, many of which affect comfort, appetite, and energy levels. These include:

• Abdominal fullness or pain: Especially under the left rib cage.
• Early satiety: Feeling full after eating small amounts, due to pressure on the stomach.
• Bloating or distension: From increased spleen size.
• Fatigue and weight loss: Due to metabolic strain and inflammation.
• Pain that radiates to the left shoulder: From nerve irritation near the spleen capsule.

In some cases, patients may not experience any symptoms, and splenomegaly is only detected during imaging or a physical examination [6].

Doctors can detect an enlarged spleen by:

• Physical examination: Feeling (palpating) the abdomen for the spleen edge below the left rib cage.
• Ultrasound or CT/MRI scans: Imaging can quantify spleen size more precisely, identifying even small increases in volume [5].
• Symptom assessment: Tracking fullness, discomfort, or early satiety helps correlate spleen size with patient experience.

Regular spleen checks help doctors adjust treatment and watch for signs the disease is getting worse.

Splenomegaly in PV is not just a symptom — it can have prognostic (predictive) significance.

• Patients with larger spleens tend to have higher white blood cell counts and more advanced disease [7].
• In long-term studies, splenomegaly has been correlated with an increased risk of myelofibrosis (bone marrow scarring) and shorter overall survival [2].
• It may also increase the risk of bleeding and thrombosis (clotting) events when combined with high blood counts [7].

Treatment for spleen enlargement focuses on controlling the underlying disease and alleviating symptoms:

1. Cytoreductive therapy: Drugs like interferon can help control blood counts and reduce spleen size over time [1].
2. JAK inhibitors: Medicines are used when PV is resistant to other treatments. They are effective in reducing spleen volume and improving related symptoms [8].
3. Phlebotomy and aspirin: While these don’t shrink the spleen directly, they lower blood thickness and help reduce symptoms.
4. Spleen-directed treatments: In rare, severe cases, radiation or surgery (splenectomy) may be considered, though these carry risks and are usually last-resort options [6].

Managing spleen symptoms is an integral part of living well with PV. Patients can:

• Eat smaller, more frequent meals to avoid discomfort from early fullness.
• Report new or worsening left-sided abdominal pain promptly.
• Keep up with regular blood tests and imaging as recommended.
• Discuss treatment options with your hematologist that target both blood counts and spleen size.

With careful monitoring and therapy, many individuals can maintain a good quality of life despite having splenomegaly.

1. What causes the spleen to enlarge in PV?

The spleen enlarges because it helps manage the excess red blood cells produced in PV. Over time, it may also begin producing blood cells on its own, especially if the bone marrow becomes scarred or less effective.

2. How common is splenomegaly in polycythemia vera?

Around 30% of PV patients have an enlarged spleen, though imaging studies suggest even more have hidden (non-palpable) enlargement. It often develops gradually as the disease progresses.

3. What are the main symptoms of an enlarged spleen?

Patients may feel fullness or pain under the left ribs, get full quickly while eating, or experience bloating and fatigue. Occasionally, there may be pain spreading to the left shoulder.

4. Does having splenomegaly mean my PV is getting worse?

Not always, but it can be a sign of more advanced disease or early transformation to myelofibrosis. Regular monitoring enables your doctor to track changes and adjust treatment as needed.

5. How is splenomegaly treated in PV?

Treatment focuses on managing the underlying PV with medications such as interferon or JAK inhibitor. In rare cases, radiation or surgery may be used if the spleen causes severe symptoms or complications.

1. Spivak, J. L. (2018). Polycythemia vera. Current treatment options in oncology, 19(2), 12.
2. Silver, R. T., Erdos, K., Taylor III, E., Scandura, J. M., & Abu-Zeinah, G. (2023). Splenomegaly (SPML) in polycythemia vera (PV): its clinical significance and its relation to symptoms, post-polycythemic myelofibrosis (PPMF) and survival. Leukemia, 37(3), 691-694.
3. Wolf BC, Banks PM, Mann RB, Neiman RS. Splenic hematopoiesis in polycythemia vera. A morphologic and immunohistologic study. Am J Clin Pathol. 1988 Jan;89(1):69-75.
4. Murphy, P., Ahmed, N., & Hassan, H. T. (2002). Increased serum levels of vascular endothelial growth factor correlate with splenomegaly in polycythemia vera. Leukemia Research, 26(11), 1007-1010.
5. Lee, M. W., Yeon, S. H., Ryu, H., Song, I. C., Lee, H. J., Yun, H. J., ... & Jo, D. Y. (2022). Volumetric splenomegaly in patients with polycythemia vera. Journal of Korean Medical Science, 37(11).
6. Aldulaimi, S., & Mendez, A. M. (2021). Splenomegaly: diagnosis and management in adults. American Family Physician, 104(2), 271-276.
7. Chou, Y. S., Gau, J. P., Yu, Y. B., Pai, J. T., Hsiao, L. T., Liu, J. H., ... & Tzeng, C. H. (2013). Leukocytosis in polycythemia vera and splenomegaly in essential thrombocythemia are independent risk factors for hemorrhage. European journal of haematology, 90(3), 228-236.
8. Vannucchi AM, Kiladjian JJ, Griesshammer M, Masszi T, Durrant S, Passamonti F, Harrison CN, Pane F, Zachee P, Mesa R, He S, Jones MM, Garrett W, Li J, Pirron U, Habr D, Verstovsek S. Ruxolitinib versus standard therapy for the treatment of polycythemia vera. N Engl J Med. 2015 Jan 29;372(5):426-35.