Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 1999;59(11):3059-3060

See related article on mastocytosis.

What is mastocytosis?

Mastocytosis (say “mas-toe-sigh-toe-sis”) is a rare disease of the skin (the most common form), or of other parts of the body (very rare), like the stomach, the intestines and the bone marrow. It's caused by having too many mast cells. Mast cells are a kind of blood cell.

Mastocytosis can occur at any age. It's more serious in adults. It's usually mild in children, and they often outgrow it.

What are mast cells?

Mast cells are made by your bone marrow. They're part of your immune system. They help you fight off infections. There are more of them in the skin, the lungs and the intestines. Mast cells make a chemical called histamine. Histamine can cause swelling, itching and redness when your body reacts to something like an insect bite or a bee sting.

What causes mastocytosis?

We don't know what causes mastocytosis. We do know some things that trigger the release of histamine and cause symptoms. Symptoms may be triggered by cold or heat, certain medicines, emotional stress and insect bites. The triggers aren't the same in every person.

What are the symptoms of mastocytosis?

The symptoms are different, depending on where the extra mast cells are. You might have a red and itchy rash if there are too many mast cells in your skin. You could get hives or have a rash that looks like freckles. If you rub the rash, it can get red and swollen. Sometimes the mast cells collect at one spot in your skin and cause one large lump.

You might have diarrhea and stomach pain if the mast cells are in your stomach and intestines. (This is rare).

In a few patients, the extra mast cells cause a serious reaction, like a bad allergy reaction. The blood pressure may suddenly drop to a low level and cause fainting. The person may have trouble breathing. This reaction can cause death if treatment isn't started right away. (This kind of severe reaction is very rare.)

  • Red, itchy rash

  • Rash that looks like freckles

  • Hives

  • One large lump on the skin

  • Diarrhea

  • Stomach pain

  • Fainting

  • Difficulty breathing

How does my doctor know I have mastocytosis?

The symptoms of mastocytosis can be like the symptoms of many other health problems. Your doctor may do a skin biopsy to find out what you have. Your doctor removes a small piece of skin and puts it under a microscope to look for extra mast cells. When an adult gets mastocytosis, a bone marrow biopsy may be needed to look for other blood diseases that might come along with the mastocytosis.

If you don't have a rash but you have other symptoms, like diarrhea, your doctor may do a blood test or a urine test.

How is mastocytosis treated?

Antihistamines, which are often used to treat allergies, are helpful. If a rash bothers you, your doctor may suggest that you be treated with ultraviolet light. If you have diarrhea, an oral version of a medicine called cromolyn (brand name: Gastrocrom) may help.

Treatment can stop your mast cells from releasing histamine. It can also keep the histamine from causing problems. You need to get treatment if your symptoms are severe.

Because mastocytosis can cause a severe allergy reaction, keep an emergency kit with you at all times so you can give yourself medicine to stop a bad reaction.

The best treatment for mastocytosis may be to stay away from the things that trigger your symptoms. It may help if you and your doctor list all the things that cause your symptoms. Did your symptoms start after you were exposed to heat or cold? Emotional stress? A medicine? An insect bite? Share what you learn with your doctor.

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