Mast cell activation syndrome

Mast cell activation syndrome (MCAS) is one type of mast cell activation disorder (MCAD), and is an immunological condition in which mast cells inappropriately and excessively release chemical mediators, resulting in a range of chronic symptoms, sometimes including anaphylaxis or near-anaphylaxis attacks.[1][2][3] Primary symptoms include cardiovascular, dermatological, gastrointestinal, neurological and respiratory problems.[2]

Mast cell activation syndrome
SpecialtyImmunology (Allergy)

Unlike mastocytosis, another type of MCAD, where patients have an abnormally increased number of mast cells, patients with MCAS have a normal number of mast cells that do not function properly and are defined as "hyperresponsive".[2] MCAS is still a poorly understood condition and is a current topic of research.[4]

Signs and symptomsEdit

MCAS is a condition that affects multiple systems, generally in an inflammatory manner. Symptoms typically wax and wane over time, varying in severity and duration. Many signs and symptoms are the same as those for mastocytosis, because both conditions result in too many mediators released by mast cells.[5] It has many overlapping characteristics with recurrent idiopathic anaphylaxis, although there are distinguishing symptoms, specifically hives and angioedema.[6]

Common symptoms include:[4][7]

  • Dermatological
    • flushing
    • hives
    • easy bruising
    • either a reddish or a pale complexion
    • itchiness
    • burning feeling
    • dermatographism
  • Cardiovascular
  • Gastrointestinal
    • diarrhea and/or constipation, cramping, intestinal discomfort
    • nausea, vomiting, acid reflux
    • swallowing difficulty, throat tightness
  • Respiratory
    • congestion, coughing, wheezing
  • Anaphylaxis If too many mediators are released into a patient's system, they may also experience anaphylaxis, which primarily includes: difficulty breathing, itchy hives, flushing or pale skin, feeling of warmth, weak and rapid pulse, nausea, vomiting, diarrhea, dizziness and fainting.


There are no known causes, but the condition appears to be inherited in some patients.[8] Symptoms of MCAS are caused by excessive chemical mediators inappropriately released by mast cells. Mediators include leukotrienes, histamines, prostaglandin, and tryptase. The condition may be mild until exacerbated by stressful life events, or symptoms may develop and slowly trend worse with time.[4][8]


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 ([9] 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.[10]


MCAS is often difficult to identify due to the heterogeneity of symptoms and the "lack of flagrant acute presentation."[7] The condition can also be difficult to diagnose, especially since many of the numerous symptoms are non-specific in nature. Mast cell activation was assigned an ICD-10 code (D89.40, along with subtype codes D89.41-43 and D89.49) in October 2016.

Although different diagnostic criteria are published, a commonly used strategy to diagnose patients is to use all three of the following:
  1. Symptoms consistent with chronic/recurrent mast cell release:
    Recurrent abdominal pain, diarrhea, flushing, itching, nasal congestion, coughing, chest tightness, wheezing, lightheadedness (usually a combination of some of these symptoms is present)
  2. Laboratory evidence of mast cell mediator (elevated serum tryptase, N-methyl histamine, prostaglandin D2 or 11-beta- prostaglandin F2 alpha, leukotriene E4 and others)
  3. Improvement in symptoms with the use of medications that block or treat elevations in these mediators"[4]

The World Health Organization has not published diagnostic criteria.


Common pharmacological treatments include:


The prognosis of MCAS is uncertain because of lack of studies.[13]


MCAS is a relatively new diagnosis, being unnamed until 2007, and is believed to be under-diagnosed.


The condition was hypothesized by the pharmacologists John Oates and Jack Roberts of Vanderbilt University in 1991, and following a build-up of evidence featured in papers by Sonneck et al.[14] and Akin et al.,[15] finally named in 2007.[5]

Diagnostic criteria were proposed in 2010.[2]

See alsoEdit


  1. ^ Valent P (April 2013). "Mast cell activation syndromes: definition and classification". Allergy. 68 (4): 417–24. doi:10.1111/all.12126. PMID 23409940. S2CID 43636053.
  2. ^ a b c d Akin C, Valent P, Metcalfe DD (December 2010). "Mast cell activation syndrome: Proposed diagnostic criteria". The Journal of Allergy and Clinical Immunology. 126 (6): 1099–104.e4. doi:10.1016/j.jaci.2010.08.035. PMC 3753019. PMID 21035176.
  3. ^ Akin C (May 2015). "Mast cell activation syndromes presenting as anaphylaxis". Immunology and Allergy Clinics of North America. 35 (2): 277–85. doi:10.1016/j.iac.2015.01.010. PMID 25841551.
  4. ^ a b c d White A (17 February 2015). "A Tale of Two Syndromes – POTS and MCAS"". The Dysautonomia Dispatch. Dysautonomia International.
  5. ^ a b c d Afrin LB, Molderings GJ (February 2014). "A concise, practical guide to diagnostic assessment for mast cell activation disease". World Journal of Hematology. 3 (1): 1–7. doi:10.5315/wjh.v3.i1.
  6. ^ a b c d e Frieri M (June 2018). "Mast Cell Activation Syndrome". Clinical Reviews in Allergy & Immunology. 54 (3): 353–365. doi:10.1007/s12016-015-8487-6. PMID 25944644. S2CID 5723622.
  7. ^ a b Afrin L (2013). "Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome.". Mast Cells: Phenotypic Features, Biological Functions and Role in Immunity. Nova Science. pp. 155–232. Archived from the original on 2018-08-18. Retrieved 2015-10-13.
  8. ^ a b Milner K (2015). "Research Update: POTS, EDS, MCAS Genetics". Dysautonomia International Conference & CME. Washington DC:
  9. ^ "About MCAS | Mast Cell Action". Retrieved 2020-03-26.
  10. ^ Akin C (August 2017). "Mast cell activation syndromes". The Journal of Allergy and Clinical Immunology. 140 (2): 349–355. doi:10.1016/j.jaci.2017.06.007. PMID 28780942.
  11. ^ Finn DF, Walsh JJ (September 2013). "Twenty-first century mast cell stabilizers". British Journal of Pharmacology. 170 (1): 23–37. doi:10.1111/bph.12138. PMC 3764846. PMID 23441583. A diverse range of mast cell stabilizing compounds have been identified in the last decade from; natural, biological and synthetic sources to drugs already in clinical uses for other indications. Although in many cases, the precise mode of action of these molecules is unclear, all of these substances have demonstrated mast cell stabilization activity and therefore may have potential therapeutic use in the treatment of allergic and related diseases where mast cells are intrinsically involved.Table 1: Naturally occurring mast cell stabilizers
  12. ^ Weng Z, Zhang B, Asadi S, Sismanopoulos N, Butcher A, Fu X, et al. (2012). "Quercetin is more effective than cromolyn in blocking human mast cell cytokine release and inhibits contact dermatitis and photosensitivity in humans". PLOS ONE. 7 (3): e33805. Bibcode:2012PLoSO...733805W. doi:10.1371/journal.pone.0033805. PMC 3314669. PMID 22470478.
  13. ^ Weiler CR, Austen KF, Akin C, Barkoff MS, Bernstein JA, Bonadonna P, et al. (October 2019). "AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management". The Journal of Allergy and Clinical Immunology. 144 (4): 883–896. doi:10.1016/j.jaci.2019.08.023. PMID 31476322. Retrieved 27 April 2020.
  14. ^ Sonneck K, Florian S, Müllauer L, Wimazal F, Födinger M, Sperr WR, Valent P (2007). "Diagnostic and subdiagnostic accumulation of mast cells in the bone marrow of patients with anaphylaxis: Monoclonal mast cell activation syndrome". International Archives of Allergy and Immunology. 142 (2): 158–64. doi:10.1159/000096442. PMID 17057414. S2CID 25058981.
  15. ^ Akin C, Scott LM, Kocabas CN, Kushnir-Sukhov N, Brittain E, Noel P, Metcalfe DD (October 2007). "Demonstration of an aberrant mast-cell population with clonal markers in a subset of patients with "idiopathic" anaphylaxis". Blood. 110 (7): 2331–3. doi:10.1182/blood-2006-06-028100. PMC 1988935. PMID 17638853.

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