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Systemic mastocytosis
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Systemic mastocytosis

Systemic mastocytosis is a blood disorder characterized by the abnormal accumulation of mast cells in various body tissues, leading to a wide range of symptoms and potential organ dysfunction.

Overview

Systemic mastocytosis is a blood disorder that can affect many different body systems. While individuals with the condition can develop signs and symptoms at any age, it usually appears after adolescence. The condition is estimated to occur in 1 per 10,000 to 20,000 individuals worldwide.

Symptoms

Signs and symptoms of systemic mastocytosis vary based on the subtype but often include:

  • Extreme tiredness (fatigue)
  • Skin redness and warmth (flushing)
  • Nausea, abdominal pain, bloating, and diarrhea
  • Backflow of stomach acids into the esophagus
  • Nasal congestion and shortness of breath
  • Low blood pressure (hypotension), lightheadedness, and headache
  • Attention or memory problems, anxiety, or depression
  • Urticaria pigmentosa: A skin condition characterized by raised patches of brownish skin that sting or itch with contact or temperature changes
  • Severe allergic reactions (anaphylaxis), which occur in nearly half of affected individuals

Causes & Risk Factors

Systemic mastocytosis occurs when mast cells, a type of white blood cell produced in the bone marrow, abnormally accumulate in tissues. In most cases, this is caused by a somatic mutation in the KIT gene, which is acquired during a person's lifetime rather than inherited.

The KIT gene mutation results in a protein that is constantly "turned on," leading to overactive signaling pathways that increase the production and accumulation of mast cells. These cells can gather in the bone marrow, gastrointestinal tract, and other tissues. When activated by environmental triggers, these excess mast cells release mediator proteins that cause an increased immune response.

Common triggers include:

  • Changes in temperature
  • Friction and minor trauma
  • Surgery
  • Insect stings
  • Vaccines
  • Anxiety and stress
  • Certain medications, including aspirin, opioids, or non-steroidal anti-inflammatory drugs (NSAIDs)

Types & Prognosis

There are five subtypes of systemic mastocytosis, differentiated by severity:

  • Indolent and Smoldering: The mildest forms. Indolent is the most common type. Individuals with these forms generally have a normal or near-normal life expectancy.
  • Aggressive Systemic Mastocytosis, Systemic Mastocytosis with an Associated Hematologic Neoplasm, and Mast Cell Leukemia: These severe types are associated with a reduced life span. They often involve organ dysfunction, such as fluid buildup in the abdomen (ascites), bone tissue loss (osteoporosis and osteopenia), and blood cell disorders or cancer. Mast cell leukemia is the rarest and most severe form.

Frequently Asked Questions

Sudden swelling of the face or throat, difficulty breathing, a rapid drop in blood pressure, severe hives, and a feeling of impending doom are classic signs. If any of these appear, use an epinephrine auto‑injector immediately and call emergency services.
Daily antihistamines (H1 and H2 blockers) and mast‑cell stabilizers (like cromolyn) can blunt mediator release. Avoid known triggers such as extreme temperatures, alcohol, certain foods, and stress. Wearing loose, breathable clothing and keeping a symptom diary helps identify personal triggers.
serum tryptase level above 20 ng/mL is highly suggestive. A bone‑marrow biopsy with immunohistochemistry for CD117 and CD25, plus PCR for the KIT D816V mutation, provides definitive proof. Elevated tryptase, a positive KIT mutation, and increased mast cells in tissue are the hallmarks.
If you develop persistent abdominal pain, diarrhea, liver or spleen enlargement, bone pain, or unexplained fatigue, consult a hematologist or a specialist in mast cell disorders. They may initiate targeted therapy such as tyrosine‑kinase inhibitors (e.g., midostaurin) or consider stem‑cell transplantation in severe cases.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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