What to Know About Indolent Systemic Mastocytosis (ISM)

Patient Portrayal
What is Indolent Systemic Mastocytosis?
ISM is a rare disease that affects the production and accumulation of mast cells, a type of white blood cell.
Normally, your body makes mast cells as part of your immune response, but a buildup of mast cells in different parts of the body can lead to symptoms similar to severe allergic reactions.

What causes ISM?
In about 95% of cases, ISM is thought to be caused by a gene mutation called KIT D816V.
How many people have ISM?
Systemic mastocytosis (SM) is a rare condition that affects around 1 in 10,000 patients. The most common form of SM is Indolent Systemic Mastocytosis (ISM), which accounts for around 75-90% of cases of SM.
What are some of the common symptoms of ISM?
Skin lesions and rash
Potentially severe allergic reactions including anaphylaxis
Nausea, vomiting and diarrhea
Other symptoms:
Each patient with ISM may experience different symptoms in different ways. Several symptoms are associated with ISM, including:
- Brain fog
- Dizziness
- Headache
- Fatigue
- Flushing
- Bone pain
- Itching
- Spots on the skin
- Abdominal pain
- Diarrhea
- Nausea
Talk to your doctor about your symptoms and for medical advice.
How is ISM diagnosed?
ISM is diagnosed by a doctor who may:
- Take biopsies (bone and/or organ)
- Measure signs of excess mast cells
- Test for KIT D816V gene mutation
- Test for serum tryptase
KIT D816V testing
A KIT D816V blood test may be helpful to aid in the diagnosis of patients who are being evaluated for ISM. Since the gene mutation is found in approximately 95% of ISM cases, measurement of this genetic marker can help evaluate for ISM. There are different types of KIT tests available that vary in sensitivity. High-sensitivity tests may be required to detect the mutation.
Symptom Triggers
ISM symptoms may occur in response to certain triggers. These can differ from person to person, but some common ISM symptom triggers may include:
- Alcohol
- Certain foods
- Skin irritation
- Exercise
- Changes in temperature
- Anxiety and stress
- Certain medications
- Insect stings