Systematic mastocytosis is a rare disorder in which immune cells, known as mast cells, build up in various internal organs within the body. It can cause an itchy rash, headache, and nausea.

Mastocytosis is rare, affecting about 1 out of every 10,000 to 20,000 people. Although children and adults can both experience mastocytosis, it’s most common in adults.

While there’s no cure for the condition, you can manage it with medications such as antihistamines and steroid treatments. It’s very rare to have a severe case, but if you think you do, it’s a good idea to contact your doctor.

Read on to learn more about systemic mastocytosis.

Mast cells are usually produced in the bone marrow and are found in connective tissues throughout the body.

If you are exposed to an allergen, your immune system senses a foreign particle, triggering mast cells to release an inflammatory substance called histamine.

Mastocytosis is a group of disorders where many mast cells develop and build up in the tissues. There are two main types:

  • Cutaneous: mast cells build up only in the skin
  • Systemic: mast cells accumulate in internal organs such as the liver, spleen, small intestine, and bone marrow

Indolent systemic mastocytosis is the most common form of the condition. It’s associated with fewer mast cells, so it usually causes less severe symptoms. It rarely progresses to a more advanced form of mastocytosis.

Mutations in the KIT gene can cause systemic mastocytosis. The KIT gene encodes a protein that controls cell growth and migration. When this gene undergoes a mutation, it may lead to overproduction of mast cells. These cells then accumulate in parts of the body where they aren’t needed.

Some common skin symptoms of systemic mastocytosis are itching and flushing. If the condition is systemic, it means you’ll have symptoms affecting the rest of your body.

Because systemic mastocytosis may affect different organs in the body, you may experience symptoms elsewhere than the skin. Some additional symptoms of systemic mastocytosis are:

  • headache
  • abdominal or stomach pain
  • nausea or vomiting

Intestinal malabsorption may occur, which means that the body has difficulty absorbing fluid and nutrients from food. Signs of this include:

  • diarrhea
  • muscle or bone pain
  • mood changes
  • fatigue

When mast cells build up, you may also experience symptoms similar to a severe allergic reaction. This can include flushing of the skin, low blood pressure, and fainting. In rare cases, this may be life threatening.

There’s no cure for systemic mastocytosis, so treatment mainly involves relieving the effects of mast cell overgrowth and avoiding dietary and environmental triggers. Examples of triggers include:

  • extreme heat or cold
  • skin irritation
  • exercise
  • emotional stress
  • insect stings
  • spicy foods
  • alcohol (if you drink)
  • certain medications

Since mast cells are producers of histamine, antihistamines are usually a component of the treatment plan. These can help manage many of the skin and gastrointestinal symptoms. Mast cell stabilizers, such as cromolyn sodium, can also prevent the release of histamine.

The goal of most other treatment options is to manage the effects of systemic mastocytosis. These may include:

  • Proton pump inhibitors: These work by reducing the production of stomach acid, helping with gastrointestinal symptoms.
  • Oral steroids: These improve nutrient uptake.
  • Epinephrine: You may need this to treat anaphylaxis (severe allergic reaction) or low blood pressure.

If you have a more aggressive form of systemic mastocytosis, you might need further treatments like interferon, immune modulators, chemotherapy drugs, or targeted therapies. Your doctor might also recommend ways to manage side effects, like osteoporosis treatment for bone loss and transfusions for anemia and low platelet counts.

Although aggressive forms of systematic mastocytosis are rare, they can be very serious. The mast cells can progressively accumulate in the organs, and over time, this may cause complications.

In even rarer cases, systemic mastocytosis can cause mast cell leukemia. This is an aggressive cancer characterized by the accumulation of mast cells within the blood or bone marrow.

In 2017, the Food and Drug Administration (FDA) approved a medication called midostaurin (Rydapt) to treat the aggressive forms of systemic mastocytosis. In a phase 2 clinical study, 60% of people experienced at least some relief in their symptoms.

To diagnose systemic mastocytosis, your doctor may order tests including:

  • bone marrow biopsy
  • bloodwork and a urinalysis to check for mast cell markers
  • imaging to determine what organs may be involved
  • genetic testing

Even though genetic mutation may cause systemic mastocytosis, it’s generally not an inherited disease.

The mutations that cause the condition are typically new and occur after conception. As a result, they only occur in certain cells of the body. Unless these mutations occur in the egg or sperm, which is very rare, they do not pass on to future generations.

Because systemic mastocytosis is so rare, it’s important to work with a specialist who is familiar with the condition.

Your doctor may be able to connect you with experts like allergists, immunologists, or hematologists. The American Academy of Allergy, Asthma, & Immunology also provides an online database to find allergists and immunologists near you.

The outlook is generally favorable for people with indolent systemic mastocytosis. The condition progresses fairly slowly and usually doesn’t have a significant effect on their lifespan.

More aggressive forms of the disease affect multiple organ systems and are generally associated with a less favorable outlook. For example, the condition may lead you to develop mast cell leukemia. While this condition is rare, it has a less favorable outlook and lower survival rates.

Accumulation of mast cells causes systemic mastocytosis in various organs throughout the body. This can cause skin conditions, gastrointestinal symptoms, and allergic reaction symptoms.

For people with indolent systemic mastocytosis, the outlook may be fairly positive. You can usually manage symptoms using a combination of antihistamines and other medications.

If you think you may have systemic mastocytosis, talk with a healthcare professional to determine if your symptoms should be evaluated by a specialist.