MCAS (Mast Cell Activation Syndrome) — Is that a real disease? (citations)

3 min readOct 17, 2018

by Russell Johnston, last edited February 23, 2019

Bad news first: the WHO doesn’t recognize it… yet. Which doesn’t mean you can’t die from it. You certainly can.

“the World Health Organization 2008 classification scheme … does not recognize MCAS” [1]

(The WHO does recognize Systemic Mastocytosis (SM), which involves having too many mast cells.)

But the good news is that there are ICD-10-CM codes for Mast Cell Activation Syndrome as of 2016. ICD = International Classification of Diseases, which is created and updated by the U.S. National Center for Health Statistics (NCHS).
https://tmsforacure.org/icd-10-cm/

Quick history of Mast Cell Activation Syndrome:
MCAS was suggested in the literature for decades according to Wikipedia.

It was suggested in 1991 and named in 2007 according to this source:
https://experts.umn.edu/en/publications/presentation-diagnosis-and-management-of-mast-cell-activation-syn

2012 “Consensus Proposal”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3224511/

Akin article 2014
https://www.jaci-inpractice.org/article/S2213-2198(14)00098-1/fulltext

Recognition of more widespread effects of MCAS is dawning slowly:
Mast cell activation disease: An underappreciated cause of neurologic and psychiatric symptoms and diseases.
https://www.ncbi.nlm.nih.gov/pubmed/26162709

Perhaps the best “evidence for” MCAS come from its connection to Ehlers-Danlos Syndrome.

Increasingly, MCAS is recognized as being comorbid (and perhaps even uniformly comorbid according to very preliminary studies) with Ehlers-Danlos Syndrome (EDS) especially Hypermobile EDS (hEDS.) That is, it may be that if you have hEDS, you have MCAS (but not necessarily vice versa.)
http://www.jacionline.org/article/S0091-6749(14)02927-3/fulltext
https://www.hoffmancentre.com/2017/11/tell-mast-cell-activation-syndrome/

In that regard, the alpha-tryptasemia study no doubt covers a large segment of hEDS cases and is our best evidence so far not only of the above comorbidity, but of a necessary (not sufficient) genetic trait that underlies this group of hEDS cases.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5397297/
https://www.ncbi.nlm.nih.gov/pubmed/30007465

There is a test for this genetic trait available:
https://www.genebygene.com/products/TPSAB1-Copy-Number---Clinical

So if your doctor or even allergist doesn’t recognize MCAS that’s not crazy, but they aren’t exactly ahead of the curve, or up to date on the literature, either. Doctors rarely are, if only because they have another job: treating patients (in many countries doctors aren’t paid to read, just to treat.) Some delay in uptake of empirical research is understandable (and even prudent) but this delay is extreme in current medical practice, and very general — it applies to a lot more than MCAS and diagnosis:

“One study in medicine, for example, examined the aftermath of nine different major treatment discoveries such as the finding that the pneumococcus vaccine protects not only children but also adults from respiratory infections, one of our most common killers. On average, the study reported, it took doctors seventeen years to adopt the new treatments for at least half of American patients.”
- The Checklist Manifesto, by Atul Gawande, p133

For a more current look at #MCASdenial and the phrase “True allergies,” see my article:
Understanding why MCAS (Mast Cell Activation Syndrome) triggers do what they do

If you are interested in knowing more about MCAS:

I can recommend an excellent 2017 article:
https://www.hoffmancentre.com/mast-cell-activation-syndrome-histamine-immune-system-runs-rampant/

MCAS (Mast Cell Activation Syndrome) — Is that a real disease? (citations)

Written by Russell Irvin Johnston

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