Medically reviewed by Gagandeep Brar, MD

• Avoid triggers, but carry an epinephrine pen for emergency treatment of anaphylaxis for when triggers are unavoidable or unknown.
• Antihistamines are a key part of treatment for both skin and gastrointestinal symptoms. 
• You may need additional treatments for skin or gastrointestinal symptoms that aren’t manageable with antihistamines or for bone disease.

Treatment for indolent systemic mastocytosis (ISM) largely focuses on preventing and controlling specific symptoms and anaphylaxis. Newer treatments work by targeting the root cause of the condition.

The First Step: Avoid Triggers 

An important part of treatment for ISM is avoiding the things that trigger your symptoms. 

Potential triggers of ISM include:

• Heat, cold, or changes in temperature
• Exercise
• Sleep deprivation
• Stress and anxiety
• Alcohol
• Certain foods 
• Certain medications, such as aspirin, opiate medications, or dyes used in medical imaging
• Bee or wasp stings

Editor’s Note: The abnormal and excessive mast cells present in ISM release large amounts of a molecule called histamine, which causes symptoms. Some of the most common ISM treatments, called antihistamines, work by blocking the receptors for these histamines.

Skin Treatments

Skin symptoms, such as itchy skin with raised red streaks, are some of the most common symptoms in ISM. 

What's usually used: H1 antihistamine

For skin symptoms, you’d usually start with an oral medication called an H1 antihistamine. Many of these medications are available over-the-counter, but your healthcare provider might write you a prescription if you need to take them at higher-than-normal doses. 

You might recognize these drugs from their use in treating seasonal allergies. Examples of H1 antihistamines are: 

• Benadryl (diphenhydramine)
• Vistaril (hydroxyzine)
• Zyrtec (cetirizine)
• Claritin (loratadine)
• Clarinex (desloratadine)

The last three are newer drugs that don’t have the same side effects of sleepiness as the older ones, so you might prefer them.

If those don't work

If H1 antihistamines don’t work, you might try another class of oral drugs called leukotriene antagonists. They are usually used for asthma, but they can also help with ISM. Examples are Singulair (montelukast) and Accolate (zarfirlukast).

If these aren’t sufficient, other potential options include:

• Oral aspirin
• Corticosteroid creams (used temporarily)
• Ultraviolet light phototherapy

Gastrointestinal Treatments

Some people with ISM get symptoms like abdominal pain, nausea, diarrhea, and gastroesophageal reflux-related heartburn. Another group of oral antihistamines, called H2 antihistamines, block histamine in receptors mostly found in your stomach. You might need to take these in addition to H1 antihistamines. 

What's usually used: H2 antihistamine

Some examples of H2 antihistamines are:

• Zantac (ranitidine)
• Pepcid (famotidine)
• Tagamet (cimetidine)

These are the same medications many people use over-the-counter for symptoms like heartburn after meals. However, you might get a prescription if you need a higher dose. 

If those don't work

If H2 antihistamines don’t work, you might need to try another kind of medication called a proton pump inhibitor, also available over-the-counter. Examples are Prilosec (omeprazole) and Protonix (pantoprazole). 

If you are still having symptoms, you might need to try an oral medication called Gastrocom (cromolyn sodium). It might help improve your skin symptoms as well.

Providers sometimes prescribe oral corticosteroids like prednisone for symptoms that are hard to treat. However, you usually can’t use these long-term due to their side effects.

Bone Treatments

Some people with ISM experience bone issues, especially bone weakening from osteoporosis. 

What's usually used: Bisphosphonates

Bisphosphonates are a group of medications commonly used in age-related osteoporosis. These come in both oral and intravenous (through the vein) forms. Some examples of bisphosphonates are:

• Fosamax (alendronate)
• Actonel (risedronate)
• Aredia (pamidronate)
• Reclast (zoledronate)

If those don't work

If bisphosphonates aren’t effective, you might be prescribed a newer osteoporosis medication, Prolia (denosumab), which is given as an injection.

Could a supplement help? You may need to take supplemental vitamin D and calcium to help prevent and treat bone issues. 

Anaphylaxis Treatments

ISM can lead to episodes of lightheadedness, fainting, low blood pressure, and increased heart rate. At the extreme, these can be signs of anaphylaxis, in which swelling and narrowing of your airway make it difficult to breathe. This can happen after a trigger, but sometimes no trigger can be found. 

Everyone with ISM needs to carry emergency self-injectable epinephrine in case they experience anaphylaxis. You’ll also need someone to evaluate you in a medical setting, and you might need additional treatments like intravenous fluids. 

Treatments To Prevent Anaphylactic Episodes

Taken regularly, both H1 and H2 antihistamines help prevent future episodes of anaphylaxis. Singulair (montelukast) can also work to prevent anaphylaxis.

Taking a newer injectable therapy, Xolair (omalizumab), may also help prevent episodes. However, it isn’t approved by the U.S. Food and Drug Administration for ISM, so some insurance plans might not cover it. Xolair may also help reduce other symptoms of ISM, like skin symptoms. 

Medications To Decrase Mast Cells

In ISM, your body makes large amounts of abnormal mast cells. Some people with ISM need therapies that reduce their mast cell numbers. Two examples are Intron A (interferon alpha-2b) and Mavenclad (cladribine). Usually, though, you don’t need these kinds of therapies unless you have severe symptoms, like significant bone disease that isn’t improving with standard treatments.

A newer medication, Ayvakit (avapritinib), works by targeting the gene mutation (gene KIT D816V) that causes the overproduction of abnormal mast cells in the first place.

Next Steps

• Keep a diary of your symptoms so you can try to identify potential triggers of ISM symptoms.
• Practice with your EPI-Pen trainer so you know how to use your EPI-Pen if you are having anaphylaxis.
• Talk to your provider about Xolair or other options if you're still experiencing symptoms with treatment.

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Kristina Dawson