"Mast cells are allergy cells responsible for immediate allergic reactions. They cause allergic symptoms by releasing products called “mediators” stored inside them or made by them. In allergic reactions, this release occurs when the allergy antibody IgE, which is present on the mast cell surfaces, binds to proteins that cause allergies, called allergens. This triggering is called activation, and the release of these mediators is called degranulation." [1]
"MCAS is a condition in which the patient experiences repeated episodes of the symptoms of anaphylaxis – allergic symptoms such as hives, swelling, low blood pressure, difficulty breathing and severe diarrhea. High levels of mast cell mediators are released during those episodes."
Heart related symptoms: tachycardia, hypotension, syncope
Skin related symptoms: itching, hives, swelling and flushing
Lung related symptoms: wheezing, shortness of breath and harsh noises while breathing that occurs with throat swelling
Gastrointestinal tract symptoms: diarrhea, nausea with vomiting and crampy abdominal pain
The treatment of acute episodes should follow the recommendations for treatment of anaphylaxis, starting with epinephrine, if indicated by the severity of symptoms.
Antihistamines, such as the first generation histamine type 1 receptor blockers diphenhydramine and hydroxyzine, can be effective for itching, abdominal discomfort and flushing, but their use may be limited by side effects (sleepiness). Second generation antihistamines, including loratadine, cetirizine and fexofenadine, are preferable due to fewer side effects.
Treatment with histamine type 2 receptor blockers, such as ranitidine or famotidine, can be helpful for abdominal pain and nausea.
Aspirin blocks production of prostaglandin D2 and can reduce flushing.
Montelukast and zafirlukast block the effects of leukotriene C4 (LTC4) and zileuton blocks LTC4 production, so these reduce wheezing and abdominal cramping.
Corticosteroids are helpful for edema, hives and wheezing but should only be used as a last resort.
Omalizumab (which blocks binding of IgE to its receptors) has been reported to reduce mast cell reactivity and sensitivity to activation which can reduce anaphylactic episodes.
