MSD Manual

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Peter J. Delves

, PhD, University College London, London, UK

Last full review/revision Oct 2020| Content last modified Sep 2022
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 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 is rare. It differs from typical allergic reactions because it is chronic rather than episodic.

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 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 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.

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

Types of mastocytosis

Mastocytosis may affect primarily the skin (called cutaneous mastocytosis) or other parts of the body (called systemic mastocytosis).

  • Cutaneous mastocytosis: 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 only rarely progresses to systemic mastocytosis in children but may do so more often in adults.

  • Systemic mastocytosis: 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

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 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. The abdomen may enlarge if the liver and spleen malfunction, causing fluid to accumulate within the abdomen.

If bone marrow is affected, bone pain 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

  • A doctor's evaluation

  • Biopsy

  • Sometimes blood tests to rule out other disorders

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

A biopsy can confirm the diagnosis of mastocytosis. Usually, a sample of skin tissue is removed and examined under a microscope for mast cells. Sometimes a sample is taken from the bone marrow.

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.

  • Blood and urine tests to rule out disorders that cause similar symptoms

  • A bone scan

  • Tests for the genetic mutation present in many people with mastocytosis

  • 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, 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 blockers. H1 blockers (commonly called antihistamines) 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, given by mouth, can relieve digestive problems and bone pain. 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, 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.

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