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Pathophysiology
Everyone has mast cells in their body, and they play many complex roles in keeping us healthy. Mast cells are immune system cells that can be found in the bone marrow and body tissues, internal and external, such as the skin, gastrointestinal tract, the lining of the airway, and intestines. These cells help by playing a role in the immune defense against by helping our body protect us from infection and also playing an active role in the inflammatory process. Mast cells also involved in an allergic reaction. This can range from a tiny papule from a mosquito bite or a full-blown anaphylactic reaction. Mast cells have within them small sacs, or granules, surrounded by membranes. The sacs contain many different kinds of substances called mediators, which participate in all of the roles above, including allergic response and anaphylaxis. The mediators are selectively released when there is an allergic or mast cell-based reaction. When someone is healthy mast cells function differently than someone with mast cell disease. Someone with mast cell disease, who’s mast cells may be activating inappropriately in response to triggers or may also be proliferating and accumulating in organ tissues (Jennings & Slee 2020-2021).

Mast cell activation can be localized or systemic. MCAS can present with a wide range of symptoms in multiple body systems, these symptoms may range from digestive discomfort to chronic pain, mental issues as well as an anaphylactic reaction ( The Mastocytosis Society). Some examples of  tissue specific consequences of mast cell activation include urticaria, allergic rhinitis, and wheezing. Systemic mast cell activation presents with symptoms involving 2 or more organ systems (skin: urticaria, angioedema, and flushing; gastrointestinal: nausea, vomiting, diarrhea, and abdominal cramping; cardiovascular: hypotensive syncope or near syncope and tachycardia; respiratory: wheezing; naso-ocular: conjunctival injection, pruritus, and nasal stuffiness). This can result from the release of mediators from a specific site, such as the skin or mucosal tissue, or activation of mast cells around the vasculature (Akin, 2017).

Symptoms can wax and wane over time and vary in intensity. Many times, there is histamine involvement and will include typical allergy symptoms such as itching, rashes, swelling inflammation ,and vomiting. These triggers can vary some easily recognized some not so easily recognized. These could be from chemical, food, heat cold or exercise. MCAS can present simultaneously in patients who have Ehlers Danlos Syndrome (EDS) a connective tissue disorder, or Postural Orthostatic Tachycardia Syndrome (POTS) (Mast Cell Action,2020).