Myeloproliferative Neoplasms and Your Enlarged Spleen

Myeloproliferative neoplasms are a group of diseases where the body produces too many red or white blood cells or platelets. Often, these diseases result in an enlarged spleen.

If your physician told you that you have this type of blood disorder, you might wonder, "Then why is my spleen so big?" or "What does my spleen have to do with my blood?" or even, "What is the spleen?" These are all excellent questions. 

This article explains the function of the spleen, why the spleen enlarges in myeloproliferative neoplasms, and describes the treatment options for splenomegaly (enlargement of the spleen).

What Is the Spleen?

The spleen is a relatively small organ (about the size of your fist). It sits on the left side of the abdomen underneath the ribcage. The spleen consists of two types of tissue:

• Red pulp filters the red blood cells. In the red pulp, old or misshapen red blood cells (such as sickle cells) are removed from the circulation. The red pulp also helps the body filter out infections, particularly certain bacterial infections.
• White pulp is part of the immune system. The white pulp helps produce lymphocytes, a type of white blood cell, that help make antibodies to infections or in response to immunizations.

Before birth, the spleen is the primary producer of blood cells (hematopoiesis). However, towards the end of gestation and after birth, the bone marrow takes over this production.

Why the Spleen Becomes Enlarged

Some types of myeloproliferative neoplasms result in an enlarged spleen. This enlargement occurs because the spleen can't effectively do its job when the body produces too many blood cells. Thus, it gets overworked and becomes enlarged.

Polycythemia Vera

In polycythemia vera, an excessive number of red blood cells are produced, causing the blood to thicken. This increased number of red blood cells then collect in the spleen, leading to splenomegaly.

Primary Myelofibrosis

In primary myelofibrosis, abnormal blood cells build up, causing damage to the bone marrow. In this disease, large amounts of blood stem cells become blood cells before they've adequately matured.

This process causes the blood inside the marrow to become thick, slowing the ability to make blood cells. Thus, to make up for the lack of blood cells produced in the bone marrow, the liver and spleen begin to make blood cells. The spleen's extra workload causes it to grow larger.

Essential Thrombocythemia

In essential thrombocythemia, too many platelets are made in the bone marrow. With this disease, platelets become sticky and can clump together, making it hard for the blood to flow. This clumping can increase the risk of blood clots, stroke, and heart attack. In addition, when the blood can't flow adequately, the spleen may become enlarged.

Symptoms of an Enlarged Spleen

Many people who have an enlarged spleen may not know, especially if the spleen is only slightly enlarged.

Symptoms of an enlarged spleen include:

• Fullness: A "full" sensation in the abdomen on the lower left side
• Stomach discomfort: When the spleen is significantly enlarged, it can press on the stomach, which may give you the sensation of feeling like you just ate a big meal when you only ate a small amount.
• Injury: The spleen is fragile and usually protected by the ribcage. As it enlarges, it is no longer protected and may be prone to injury, particularly trauma from a car accident or contact sport (like football or hockey). Trauma to an enlarged spleen can cause massive bleeding.

Treatment of Enlarged Spleen

If your spleen is only mildly enlarged, you may not need treatment. So, your physician will likely monitor your blood counts and the size of your spleen closely.

If your doctor recommends treatment, there are three options: medical therapy, splenectomy, and radiotherapy.

Medical Therapy

In general, medications for enlarged spleen work by reducing blood cell production. One of the most common medications used to reduce spleen size in the myeloproliferative neoplasms is hydroxyurea.

Other times, doctors use therapies to treat the underlying cause of enlarged spleen.

These may include:

• Busulfan
• Melphalan
• Alpha interferon
• Thalidomide
• Lenalidomide
• Prednisone (as supportive with thalidomide or lenalidomide)

JAK-2 inhibitors, such as the drug Ruxolitinib, can be used in some circumstances.

Second-line therapies include:

• Cladribine (also called 2CDA)
• Daunorubicin
• Decitabine
• 5-azacytidine

Treatment depends on your specific diagnosis, other medical problems, and the side effects of treatment.

Splenectomy

After medication, the second treatment choice is splenectomy, which is the surgical removal of the spleen.

The most significant risk of removing the spleen is the potential for serious life-threatening infections. If you haven't already, you should receive specific vaccines to protect you from pneumococcal and meningococcal infections before splenectomy. In addition, once the spleen is removed, you will likely be prescribed antibiotics to prevent these infections.

Radiotherapy

A third treatment option is radiotherapy (also called radiation therapy). Radiation directed towards the spleen can help shrink it in size.

These effects are temporary, so splenic radiotherapy is considered palliative treatment to minimize symptoms to improve quality of life. This therapy may be a good option for people who are not candidates for splenectomy.

Summary

Myeloproliferative neoplasms are a group of blood disorders that can lead to an enlarged spleen. If you have an enlarged spleen, you may not notice it at all. However, at times, an enlarged spleen can cause symptoms like a full sensation in the abdomen, and there is an increased risk of injury when it becomes too large to be protected by the ribcage.

An enlarged spleen doesn't always require treatment. If you need treatment, it may include medication, surgery to remove the spleen, or radiation to reduce the spleen's size.

A Word From Verywell

There are many things to consider when deciding if or how to treat an enlarged spleen in polycythemia vera, primary myelofibrosis, and essential thrombocythemia. So, make sure to discuss with your physician the benefits and possible side effects of these treatments.