Mast Cell Activation Disorder

What are Mast Cells?


Mast cells are an important part of our immune system. They are a type of blood cell found in every part of the body and play a complex and vital role in keeping us healthy. One of the main functions of a mast cell is mounting an allergic response when the body senses a threat. This can range from localized swelling and irritation to widespread anaphylaxis. 


Mast cells play their part by releasing different chemical mediators when triggered by the threat, resulting in different responses throughout the body. These chemical mediators include histamines, tryptase, heparin, leukotrienes, prostaglandins, interleukins, and tumor necrosis factor-α. In a healthy individual, these chemical mediators serve to protect the body and neutralize the threat. In individuals with mast cell dysfunction, the mast cells respond inappropriately to triggers or can multiply and accumulate in organ tissue. 

L:  Woman's face/neck with red blotches. R:  Inset mast cell degranulating.

What are Mast Cell Activation Disorders?


In Mast Cell Activation Disorders (MCAD), patients’ mast cells activate at abnormal times resulting in a variety of allergic symptoms throughout the body. Respiratory symptoms may include wheezing, shortness of breath, itchy throat, or congestion. Gastrointestinal symptoms may include nausea, vomiting, diarrhea, bloating, abdominal pain, or GERD. Circulatory symptoms may include low hypotension, tachycardia, fainting, chest pain, or problems with clotting. Skin symptoms may include hives, itching, flushing (face, neck, chest), or swelling. Other symptoms include headaches, brain fog, osteoporosis, bone pain, body aches, enlarged lymph nodes, menstrual cramps, and so on.


The unpredictability of MCAD can make it difficult to manage and in some cases very disabling. Patients may struggle to determine their triggers as they can be numerous and can change over time. Potential triggers include infection, medications, venom, perfumes or odors, hot or cold environments, stress, fatigue, and so on. Symptoms may be episodic or cyclical, and may change in frequency or intensity over time. Sometimes patients whose symptoms are mild and easier to manage may suddenly experience a drastic worsening of their case.


As there is no cure for MCAD, treatment seeks to stabilize the misbehaving mast cells by utilizing a variety of different medications, depending on the patients’ symptoms. The most common medications used to treat MCAD are H1 and H2 antihistamines, anti-leukotrienes, or mast cell stabilizers. Corticosteroids, aspirin, Xolair, immune modulators, chemotherapy, or other medications may be used depending on the circumstances and severity.

Three Types


There are three types of Mast Cell Activation Disorders- primary, secondary, and idiopathic.


Primary MCAD includes Mastocystosis and Monoclonal Mast Cell Activation Syndrome. Mastocytosis is a clonal MCAD where gene mutations trigger mast cell growth receptor (KIT) to produce an abnormally high number of mast cells in the body. Most of these mutations occur spontaneously and are not inherited. The most common c-KIT mutation is D816V. The mutation may be detected with a blood test, but a bone marrow biopsy is much more accurate in finding the mutated cells. Mastocytosis can manifest as localized tumors, Cutaneous Mastocytosis, or Systemic Mastocystosis. Monoclonal Mast Cell Activation Syndrome is diagnosed in patients who have a c-KIT mutation, but do not fulfill enough of the diagnostic criteria for Mastocystosis.


Secondary MCAD occurs in patients whose mast cell activation occurs as the result of another illness. It is non-clonal and not the result of an abnormal number of mast cells in the body. A commonly cited example is IgE-mediated allergies. Typically, patients with secondary MCAD can identify the specific triggers that cause their reactions.


The third type of MCAD is Idiopathic Mast Cell Activation Syndrome (MCAS). To be diagnosed with MCAS patients’ symptoms must occur in at least two body systems and the biological cause for the symptoms must be unknown. MCAS is diagnosed after primary and secondary forms of MCAD are ruled out. Like secondary MCAD, MCAS is non-clonal and does not the result of an abnormal number of mast cells in the body. Instead, MCAS results from the abnormal behavior of mast cells.


MCAS can be a challenge to diagnose as there is no definitive test to confirm it. Serum tryptase, 24-hour urine histamine, prostaglandin D2, prostaglandin F2-alpha, and other tests may be of diagnostic use but do not always rule our MCAS. Therefore, many in the field argue that the best way to diagnose MCAS is see if patients respond to treatment. If treatment is not successful then this would suggest that the patient does not suffer from MCAS.

Additional Resources:


Curr Allergy Asthma Rep. 2013 Feb;13(1):27-32. doi: 10.1007/s11882-012-0322-z. Mast cell activation syndrome: a review.

Image source: staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. (Own work) [CC BY 3.0 (], via Wikimedia Commons