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.
• 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.

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, a component of the immune system, 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. Some people have a genetic mutation that causes mastocytosis. What causes the disorder in others is sometimes unclear.

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

• Cutaneous mastocytosis: This form 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: This form usually occurs in adults. Mast cells accumulate in the skin, stomach, intestine, liver, spleen, lymph nodes, and bone marrow (where blood cells are produced). 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.

Symptoms

A single mastocytoma does not cause symptoms. Spots and bumps may itch, particularly if they are rubbed or scratched. Itching may be worsened by changes in temperature, contact with clothing or other materials, or use of some drugs (including nonsteroidal anti-inflammatory drugs). Consuming hot beverages, spicy foods, or alcohol or exercising may also make itching worse. Rubbing or scratching the spots may result in hives and make the skin turn red.

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

Widespread reactions may occur. With systemic mastocytosis, the widespread reactions tend to be severe. They include anaphylactic and anaphylactoid reactions (see Allergic Reactions and Other Hypersensitivity Disorders: Anaphylactoid Versus Anaphylactic), which cause fainting and a life-threatening drop in blood pressure (shock). Anaphylactoid reactions resemble anaphylactic reactions, but no allergen triggers them.

Systemic mastocytosis may affect bone marrow, and up to 30% of adults with systemic mastocytosis develop cancers, particularly myelocytic leukemias. In these people, life expectancy may be shortened.

Diagnosis

Doctors suspect the diagnosis based on symptoms, particularly spots that, when scratched, result in hives and redness. A biopsy can confirm the diagnosis. 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. Blood tests to measure levels of chemical substances related to mast cells are done. High levels support the diagnosis of systemic mastocytosis.

Treatment

A mastocytoma usually disappears spontaneously. Itching may be treated with antihistamines. For children, no other treatment is needed. If adults have itching and rashes, ultraviolet light and corticosteroid creams may be applied to the skin.

Systemic mastocytosis cannot be cured, but symptoms can be controlled with antihistamines and histamine-2 (H₂) blockers, which reduce acid production in the stomach (see Peptic Disorders: Drugs Used to Treat Peptic Disorders). CromolynSome Trade Names
CROLOM INTAL
, given by mouth, can relieve digestive problems and bone pain. AspirinSome Trade Names
BAYER
can relieve flushing but may make other symptoms worse. Children are not given aspirinSome Trade Names
BAYER
because Reye's syndrome 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 (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, etoposideSome Trade Names
VEPESID
, and mercaptopurineSome Trade Names
PURINETHOL
) may help.

A self-injecting syringe of epinephrine should always be carried for prompt emergency treatment of anaphylactic or anaphylactoid reactions.

Last full review/revision August 2012 by Peter J. Delves, PhD