What is Mast Cell Activation Syndrome (MCAS)

By: Katherine Vuong

To understand the condition of Mast Cell Activation Syndrome, you must first understand the concept of Mast cells. Mast cells play an important role in the body's immune response to infections and allergens. When activated, allergy antibodies known as IgE bind to proteins and release mediator chemicals. The released mediators stimulate immune responses associated with symptoms such as headaches, hypotension, bronchoconstriction, nausea, arrhythmia, fatigue, and inflammation. While this is a normal immune system reaction, someone with MCAS will experience repeated anaphylactic episodes because of high levels of mast cell mediators.

MCAS is typically diagnosed when there is evidence of multiple anaphylactic symptoms experienced due to high levels of mast cell mediators or when a patient experiences allergic reactions to innocuous objects such as food, fragrances, and environmental changes. There are three classifications of mast cell activation disorders (MCA). Primary MCA is when categorized as an abnormal production of mast cells, whereas secondary is normal mast cells that are activated by micro-environmental triggers. The third classification, idiopathic, is considered after extensive investigation when a likely cause for the trigger cannot be identified. In some cases, mast cells can produce identical clones that are spontaneously released, stimulating these mediators and triggering an allergic reaction.

What are the symptoms of MCAS?

Symptoms of MCAS can range from mild to severe and depend upon the type of mediator released when activated. Because mast cells are found in all areas of the body, the symptoms correlate with what mediator chemicals are being released as well as where in the body they are being activated. For example, one of the most common mediators is histamine. When activated within the skin, the patient can experience irritation, swelling, hives, and dermatitis. Consequently, when activated within the gastrointestinal system, patients can experience symptoms such as diarrhea and vomiting.

Other common symptoms include:

• Itching
• Hives
• Swelling
• Flushing
• Hypotension (low blood pressure)
• Rapid pulse
• Bronchoconstriction (shortness of breath)
• Cardiac arrhythmias
• Inflammation

What is the treatment for MCAS?

MCAS can be treated both preventatively and with different medications. Patients who are diagnosed or are suspected of having MCAS should always avoid known and possible triggers. Medication options strongly depend on the treatment of specific symptoms. Antihistamines are typically the first line of defense in treating a wide range of symptoms because they act as an inverse agonist (receptor blocker) to hinder mediators from binding. Patients with MCAS should use antihistamines as a way of prophylactically treating their symptoms. It is also important for patients with MCAS to carry and be trained in using EpiPens in case of an emergency.

What medications are used to treat MCAS?

As mentioned before, certain medications are used to treat different symptoms of MCAS.

Skin - itching, flushing, hives, inflammation, raised lines or welts can be treated with.

• H1-Blockers and H2-blockers such as diphenhydramine (Benadryl) and Cimetidine (Tagamet)
• Leukotriene antagonists such as Montelukast
• Aspirin
• Ketotifen

Gastrointestinal - Diarrhea, abdominal cramping, vomiting and nausea can be treated with.

• H2-blockers such as Cimetidine
• Cromolyn Sodium
• Proton Pump Inhibitors such as omeprazole (Prilosec) and Lansoprazole (Prevacid)
• Leukotriene antagonists such as Montelukast
• Ketotifen

Neurological - Headache, brain fog, poor concentration can be treated with.

• H1-Blockers and H2-blockers such as diphenhydramine (Benadryl) and Cimetidine (Tagamet)
• Cromolyn Sodium
• Ketotifen

Cardiovascular - Light headedness, dizziness, blurry vision, fainting, increased heart rate can be treated with.

• H1-Blockers and H2-blockers such as diphenhydramine (Benadryl) and Cimetidine (Tagamet)
• Corticosteroids such as cortisone, hydrocortisone, prednisone
• Omalizumab (Xolair)

Pulmonary - Wheezing, throat swelling can be treated with.

• H1-Blockers and H2-blockers such as diphenhydramine (Benadryl) and Cimetidine (Tagamet)
• Corticosteroids such as cortisone, hydrocortisone, prednisone
• Omalizumab (Xolair)
• Leukotriene antagonists such as Montelukast

Anaphylaxis

• Epinephrine (EpiPen)
• H1-Blockers and H2-blockers such as diphenhydramine (Benadryl) and Cimetidine (Tagamet)
• Corticosteroids such as cortisone, hydrocortisone, prednisone
• Omalizumab (Xolair)

Naso-ocular - Nasal stuffiness, nasal swelling, runny nose

• H1-blockers including topical such as Olopatadine and Doxepin cream
• Topical corticosteroids such as hydrocortisone cream
• Topical formulations of Cromolyn sodium

While certain medications can help relieve the symptoms of Mast Cell Activation Syndrome (MCAS), the inactive ingredients or fillers in these medications can sometimes trigger episodes. Common fillers that may cause reactions include:

• Lactose
• Cornstarch
• Polyethylene glycol (PEG)
• Povidone
• Carboxymethylcellulose
• Gelatin
• Dyes such as brilliant blue, sunset yellow FCF, allura red, indigo carmine
• Propylene glycol
• Mannitol
• Sucrose

Compounding pharmacies, like CareFirst Specialty Pharmacy, can customize medications by removing fillers that may trigger mast cell activation. For more information, contact us at 844-822-7379.

References:

1. Bonamichi-Santos, R., & Castells, M. (2016). Mast Cell Activation Syndromes. Current Treatment Options in Allergy, 3(4), 384-400. https://doi.org/10.1007/s40521-016-0100-6
2. Frieri, M. (2018). Mast Cell Activation Syndrome. Clinical Reviews in Allergy & Immunology, 54(3), 353-365. https://doi.org/10.1007/s12016-015-8487-6