Merck Manual

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(Mast Cell Disease)


James Fernandez

, MD, PhD, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University

Reviewed/Revised Oct 2022 | Modified Mar 2023
Topic Resources

Mastocytosis is an uncommon abnormal accumulation of mast cells in the skin and sometimes in various other parts of the body.

  • People may have itchy spots and bumps, flushing, digestive upset, and sometimes bone pain or anaphylactic and anaphylactoid reactions.

  • Symptoms suggest the diagnosis, and a biopsy of the skin and/or bone marrow can confirm it.

  • If mastocytosis affects only the skin, it may resolve without treatment, but if it affects other parts of the body, it cannot be cured.

  • Antihistamines help relieve itching, and histamine-2 (H2) blockers help relieve digestive upset.

  • People with mastocytosis should always carry self-injecting syringe of epinephrine for prompt emergency treatment of anaphylactic or anaphylactoid reactions.

Mastocytosis develops when mast cells increase in number and accumulate in tissues over a period of years. Mast cells are part of the immune system Overview of the Immune System The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include Microorganisms (commonly called germs, such as bacteria, viruses, and fungi) Parasites... read more and are normally present in many body tissues, particularly the skin, lungs, and lining of the intestine. Mast cells produce histamine, a substance involved in inflammatory and allergic reactions and in the production of stomach acid. Because the number of mast cells increases, levels of histamine increase. Histamine can cause many symptoms, including digestive problems.

Mastocytosis is rare. It differs from typical allergic reactions because it is chronic rather than episodic.

Some people have a genetic mutation that causes mastocytosis. What causes the disorder in others is sometimes unclear.

Types of mastocytosis

There are two main types of mastocytosis:

  • Cutaneous mastocytosis (primarily in the skin)

  • Systemic mastocytosis (affecting organs other than the skin)

Cutaneous mastocytosis usually occurs in children. Occasionally, mast cells accumulate only as a single mass in the skin (mastocytoma), typically before age 6 months. More commonly, mast cells congregate in many areas of the skin, forming small reddish brown spots or bumps (called urticaria pigmentosa). Urticaria pigmentosa rarely progresses to systemic mastocytosis in children but may do so more often in adults.

Systemic mastocytosis usually occurs in adults. Typically, mast cells accumulate in bone marrow (where blood cells are produced). Often, they also accumulate in the skin, stomach, intestine, liver, spleen, and lymph nodes. Organs may continue to function, with little disruption. But if many mast cells accumulate in the bone marrow, too few blood cells are produced, and serious blood disorders, such as leukemia, can develop. If many mast cells accumulate in organs, the organs malfunction. The resulting problems can be life threatening.

Images of Urticaria Pigmentosa

Mast cell activation syndrome (MCAS) develops when mast cells become overactive and release their contents, which include histamine and other substances that cause inflammation and allergy symptoms. Thus, MCAS, unlike mastocytosis, is not caused by accumulation of excess mast cells in the skin and other tissues. However, symptoms may resemble those of systemic mastocytosis. They may include a rapid heart rate, fainting, hives, flushing, nausea, vomiting, and brain fog. Symptoms may occur frequently and suddenly. MCAS should be diagnosed based on characteristic symptoms, laboratory test results, and a lessening of symptoms in response to treatment for MCAS. People are usually treated with antihistamines Antihistamines Allergic reactions (hypersensitivity reactions) are inappropriate responses of the immune system to a normally harmless substance. Usually, allergies cause sneezing, watery and itchy eyes, a... read more Antihistamines , leukotriene inhibitors Leukotriene Modifiers Drugs allow most people with asthma to lead relatively normal lives. Most of the drugs used to treat an asthma attack can be used (often in lower doses) to prevent attacks. (See also Asthma... read more Leukotriene Modifiers , and mast cell stabilizers Mast Cell Stabilizers Drugs allow most people with asthma to lead relatively normal lives. Most of the drugs used to treat an asthma attack can be used (often in lower doses) to prevent attacks. (See also Asthma... read more Mast Cell Stabilizers . Whether mast cell activation syndrome progresses to mastocytosis is unclear.

Symptoms of Mastocytosis

A single mastocytoma may not cause symptoms.

Spots and bumps may itch, particularly if they are rubbed or scratched. Itching may be worsened by the following:

  • Changes in temperature

  • Contact with clothing or other materials

  • Use of some drugs, including nonsteroidal anti-inflammatory drugs (NSAIDs)

  • Consumption of hot beverages, spicy foods, or alcohol

  • Exercise

Flushing is common.

Peptic ulcers Peptic Ulcer Disease A peptic ulcer is a round or oval sore where the lining of the stomach or duodenum has been eaten away by stomach acid and digestive juices. Peptic ulcers can result from infection with Helicobacter... read more Peptic Ulcer Disease may develop because too much histamine is produced, stimulating secretion of excess stomach acid. Ulcers can cause stomach pain. Nausea, vomiting, and chronic diarrhea may also occur. Mast cells may accumulate in the liver and spleen, causing them to malfunction. As a result, fluid may accumulate in the abdomen, causing it to enlarge.

If bone marrow is affected, bone pain and anemia can result.

People with mastocytosis may become irritable, depressed, or moody.

Systemic mastocytosis may affect bone marrow, and up to 30% of adults with systemic mastocytosis develop cancers, particularly myeloid leukemias Acute Myeloid Leukemia (AML) Leukemia is a cancer of white blood cells. White blood cells have many jobs, including helping your body's immune system fight off infection. White blood cells form in your bone marrow, the... read more . In these people, life expectancy may be shortened.

Diagnosis of Mastocytosis

  • Bone marrow biopsy

  • Sometimes blood tests

Doctors suspect mastocytosis based on symptoms, particularly spots that, when scratched, result in hives and redness.

A bone marrow biopsy can confirm the diagnosis of mastocytosis. Usually, a sample of bone marrow Bone Marrow Examination Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Sometimes a sample of bone marrow must be examined to determine... read more is removed and examined under a microscope to check for mast cells and, if they are present, to determine how many there are and what they look like. Sometimes a skin biopsy can be done to check for mast cells, but a bone marrow biopsy is still needed to check for systemic mastocytosis.

Doctors use specific criteria to diagnose mastocytosis based on results of the bone marrow biopsy, including gene tests for a specific mutation present in many people with mastocytosis, and blood tests.

If the diagnosis is unclear, doctors may do the following:

  • Blood and urine tests to measure levels of substances related to mast cells: High levels support the diagnosis of systemic mastocytosis but do not confirm it.

  • A bone scan

  • Biopsy (using an endoscope) to determine whether the number of mast cells in the digestive tract is abnormally high

Treatment of Mastocytosis

  • Drugs to relieve symptoms

  • For aggressive systemic mastocytosis, other drugs, such as interferon and prednisone, or surgery, such as splenectomy

A single mastocytoma may disappear spontaneously.

Itching due to cutaneous mastocytosis may be treated with antihistamines. For children, no other treatment is needed. If adults have itching and rashes, psoralen (a drug that makes the skin more sensitive to ultraviolet light) plus ultraviolet light or corticosteroid creams may be applied to the skin.

Systemic mastocytosis cannot be cured, but symptoms can be controlled with H1 and H2 histamine blockers. (Both of these blockers are antihistamines Antihistamines Allergic reactions (hypersensitivity reactions) are inappropriate responses of the immune system to a normally harmless substance. Usually, allergies cause sneezing, watery and itchy eyes, a... read more Antihistamines , but the term antihistamine is usually used only for H1 blockers.) H1 blockers can relieve itching. H2 blockers Histamine-2 (H2) Blockers Stomach acid plays a role in a number of disorders of the stomach, including peptic ulcer, gastritis, and gastroesophageal reflux disease (GERD). Although the amount of acid present in the stomach... read more reduce acid production in the stomach and thus relieve symptoms caused by peptic ulcers and help ulcers heal. Cromolyn, a mast cell stabilizer, is taken by mouth, and can relieve digestive problems and bone pain. Ketotifen, which is a H1 blocker and a mast cell stabilizer, is taken by mouth and may be effective. Aspirin can relieve flushing but may make other symptoms worse. Children are not given aspirin because Reye syndrome Reye Syndrome Reye syndrome is a very rare but life-threatening disorder that causes inflammation and swelling of the brain and impairment and loss of function of the liver. The cause of Reye syndrome is... read more is a risk.

If systemic mastocytosis is aggressive, the chemotherapy drugs midostaurin or avapritinib can be used. Interferon-alpha, injected under the skin once a week, may reduce the disorder’s effects on bone marrow. Corticosteroids Corticosteroids: Uses and Side Effects Corticosteroids: Uses and Side Effects (such as prednisone), taken by mouth, may also be used but only for a short time. When taken by mouth for more than 3 to 4 weeks, they can have many, sometimes serious side effects.

If many mast cells accumulate in the spleen, the spleen may be removed.

If leukemia develops, chemotherapy drugs (such as daunomycin, etoposide, and mercaptopurine) may help.

People with systemic mastocytosis should always carry a self-injecting syringe of epinephrine for prompt emergency treatment of anaphylactic or anaphylactoid reactions.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Adrenaclick, Adrenalin, Auvi-Q, Epifrin, EpiPen, Epipen Jr , Primatene Mist, SYMJEPI, Twinject
Deltasone, Predone, RAYOS, Sterapred, Sterapred DS
Alaway, Children's Alaway, Claritin Eye, Eye Itch Relief, Itchy Eye, Zaditor, Zyrtec Itchy Eye
Anacin Adult Low Strength, Aspergum, Aspir-Low, Aspirtab , Aspir-Trin , Bayer Advanced Aspirin, Bayer Aspirin, Bayer Aspirin Extra Strength, Bayer Aspirin Plus, Bayer Aspirin Regimen, Bayer Children's Aspirin, Bayer Extra Strength, Bayer Extra Strength Plus, Bayer Genuine Aspirin, Bayer Low Dose Aspirin Regimen, Bayer Womens Aspirin , BeneHealth Aspirin, Bufferin, Bufferin Extra Strength, Bufferin Low Dose, DURLAZA, Easprin , Ecotrin, Ecotrin Low Strength, Genacote, Halfprin, MiniPrin, St. Joseph Adult Low Strength, St. Joseph Aspirin, VAZALORE, Zero Order Release Aspirin, ZORprin
Etopophos, Toposar, VePesid
Purinethol, PURIXAN
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