Mast cell disease and the spleen

Spleen is known mostly for having a stupid name, but it actually does a lot of really important things.  It is located in the upper left quadrant of the abdomen.  It is essentially a filter.  It removes old or damaged red blood cells.  It retains a supply of blood that can be used to regulate blood pressure in case of hemorrhage.  It also recycles and conserves iron by metabolizing hemoglobin removed from red blood cells filtered out.  The spleen also produces antibodies and filters out bacteria and blood cells that have been attacked by antibodies and marked for removal.  In this way, it is effectively a very large lymph node. 

Another very important function of the spleen is creation of blood cells.  In cases where the bone marrow is producing fewer blood cells than normal (like myelofibrosis), the spleen can actually compensate to produce red and white blood cells.  About ¼ of the body’s white cells are stored in the spleen at any time. 
Swelling of the spleen is called splenomegaly.  If a swollen spleen can be felt manually, it is at least twice its normal size.  The spleen usually swells when it is working harder than normal.  This can happen for several reasons. 
Swelling of the spleen often has no symptoms.  It can cause abdominal, chest or back pain and the feeling of having a “small stomach,” being able to eat less than normal in one sitting.  Anemia may also be present.  The most common reason is developed countries is mononucleosis, followed by infiltration by benign or neoplastic cells, or portal hypertension.  Bacterial infections like syphilis can also cause a swollen spleen.  In people whose bone marrow is not producing enough cells, the spleen can become swollen by the effort of producing extra cells. 
It is should be stated that swelling of the spleen is pretty common in blood disorders.  It is sometimes found in systemic mastocytosis.  As the spleen gets bigger, it grows beyond the borders of the protective rib cage and can be more easily damaged.  Swollen spleens present an increased risk of rupture. 
In SM, splenomegaly (swollen spleen) is NOT a C finding indicating aggressive disease.  It is a B finding.  This is because mast cells often infiltrate the spleen, causing swelling, but not necessarily impairing function.  Hypersplenism with splenomegaly is a C finding.  Hypersplenism is when the spleen is working too hard. 
Hypersplenism is indicated by swelling of the spleen, reduction in circulating red blood cells, platelets or granulocytes (neutrophils, eosinophils, basophils or mast cells), increased proliferation by the bone marrow to compensate for the decrease in circulating cells, and probable resolution of these symptoms by removal of the spleen.    Hypersplenism can cause additional complications, including portal hypertension and ascites.
Portal hypertension is increased pressure in the vein that connects the GI tract and spleen to the liver.  Ascites is free fluid in the abdomen.  Both portal hypertension and ascites are also mastocytosis C findings.  Removal of the spleen can decrease the patient’s risk of portal hypertension and ascites, thus improving prognosis.  Additionally, in the context of mast cell disease, an infiltrated organ is inflamed, which is in turn activating to mast cells.  Removal of a source of inflammation can cause relief of systemic activation.
People living without a spleen are more susceptible to certain types of infections, including H. influenzae, S. pneumoniae, and Meningococcus spp.  They should receive vaccinations for these organisms and also regular flu vaccinations.  In some cases, long term prophylactic antibiotics are needed.  Often, patients without a spleen develop a stable high white blood cell or platelet count as their numbers are not regulated by the spleen. 

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