What is mastocytosis?

Mastocytosis is a condition where certain immune cells, called mast cells, build up under the skin and/or in the bones, intestines and other organs.

This abnormal growth of mast cells causes a range of symptoms, including itchy bumps on the skin, gastrointestinal (GI) issues such as diarrhea, and bone pain. It can increase the risk of anaphylaxis (a severe allergic response) when patients come across certain environmental triggers (such as a bee sting). In some cases, the mastocytosis can be aggressive and lead to death if left untreated. Mastocytosis is not contagious.

What are mast cells?

Mast cells are type of white blood cells located all over your body. People have the highest numbers of mast cells where the body meets the environment: the skin, lungs and intestinal tract.

Normally, mast cells are part of your immune system. When mast cells detect a germ or virus, they set off an inflammatory (allergic) response by releasing a chemical called histamine. This response protects your body from germs and infections.

Mast cells are also involved with other vital functions in your body. They are part of wound healing, bone growth and forming new blood vessels.

What are the types of mastocytosis?

There are two main types of mastocytosis. They are:

  • Cutaneous: This type of mastocytosis affects the skin only. It occurs more often in children. Mast cells build up in the skin, causing red or brown lesions that itch. By itself, cutaneous mastocytosis isn’t life-threatening. But people with the disorder have significant symptoms and have a much higher risk of a severe allergic reaction, which can be fatal.
  • Systemic: Occurring mainly in adults, systemic mastocytosis affects parts of the body other than the skin. Mast cells accumulate in the bone marrow and organs, such as the intestines. In cases of aggressive systemic mastocytosis, it can be life-threatening. Systemic mastocytosis includes two rare forms: mast cell leukemia and mast cell sarcoma. Mast cell sarcoma occurs when a tumor made up of mast cells forms somewhere in the body. Mast cell leukemia is a very aggressive form of the disease where large numbers of mast cells are found in the blood and bone marrow.

What causes mastocytosis?

Mastocytosis, in particular systemic mastocytosis, is often caused by a mutation (a change in the code or sequence) in a gene called KIT. The change happens after conception. In most cases, it is not inherited (passed down from one generation to another).

If you have mastocytosis, certain activities and factors can trigger an attack. What causes an attack for one person may not affect someone else. There are dozens of potential triggers. You should talk to your doctor about medications and situations you should avoid.

Some common triggers include:

  • Rubbing or friction on the skin.
  • Exercise and physical activity.
  • Insect bites (especially ant bites) and wasp and bee stings.
  • Alcohol, certain food and some medications, including nonsteroidal anti-inflammatory drugs (NSAIDS), muscle relaxers and anesthesia.
  • Sudden changes in temperature.
  • Physical or emotional stress.

Who does mastocytosis affect?

Mastocytosis can occur in children and adults. Systemic mastocytosis usually affects adults. Cutaneous mastocytosis typically appears in children, usually before the child’s second birthday. The condition affects males and females mostly equally.

How common is mastocytosis?

Mastocytosis is rare. One estimate reports that it occurs in one in every 10,000 people, while another estimate is one in every 20,000 people.

What are the symptoms of mastocytosis?

Symptoms of mastocytosis can range from mild to severe. They include:

  • Brown or red blotches on the skin, or bumps or spots that itch.
  • Skin blisters (this symptom usually occurs in children).
  • Nausea, stomach pain, diarrhea and vomiting.
  • Bone pain.
  • Flushing (when skin all over the body turns red).
  • A drop in blood pressure.
  • Fainting.

Last reviewed by a Cleveland Clinic medical professional on 09/17/2020.


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