The acronym MCD is the (new in 2022) umbrella term for ALL forms of Mast Cell Diseases or Disorders, including the very rare (thankfully) MC Leukemias, followed by the still rare but less so forms of Mastocytosis (several, including cutaneous and systemic); and lastly the newly but most poorly recognized yet quite common form of Mast Cell Activation Diseases (MCAD) now called Mast Cell Activation Syndrome or MCAS for which an ICD-10 code finally came out in October 2016.
Editor’s note 9/17/22: I’m just now re-writing this entire site to reflect the new umbrella term MCD to represent the entire collection of Mast Cell Diseases, which includes all forms of Masto, plus all forms of MCAD (MCAS, HaTS, MMAS, and anything else we uncover that involves inappropriate mast cell activation.) Please forgive any outdated or erroneous leftover writing if I haven’t quite gotten to it yet. We used to use MCAD as the umbrella term.
MCAS may run as high as 10% of the population we are now realizing. I’ve seen some sources cite as high as 14% and even higher in one case. Not rare at all! Just rarely recognized. Find best articles for your doctors to learn more here on my MCAD resources page.
All forms of MCDs, but especially MCADs cause what you might call “extra” allergies & sensitivities in the absence of elevated IgE for same that your allergist can’t easily test for due to the the lack of IgE antibodies driving it. You may have plenty of “regular” IgE-driven allergies also, but those can be diagnosed more easily and only involve organic proteins. (Pollen, dander, bugs, foods.)
Yet we suffer from over-activation of our mast or “allergy” cells which are throughout your body but especially the skin and GI tract. (I secretly wish we’d rename it “MCOAS” for Mast Cell OVER-Activation Syndrome, but that’s just me.)
It also runs in all races and ethnicities and skin types. (I’m slowly updating the below to better reflect this in 2022. Most literature only refers to the appearance in white skin yet, sorry.)
Folks with Mastocytosis have too many and/or misshapen mast cells in clumps in various places throughout the body (on the skin, and/or in the bone marrow or GI tract) which may or may not also be over-active. They may have to treat for both (over) activation and proliferation. But some just treat or monitor their proliferation.
Folks with MCAS and HaTS have normal or lower numbers of mast cells more evenly distributed (not clumped together usually, and normally shaped) but they are highly reactive and too easily triggered making them very sick still.
MCAS is not necessarily less severe than masto either – some patients with “just” MCAS can be more anaphylactoid than some masto patients. It really varies.
You can be just as reactive and go into anaphylaxis from any form of MCAD as from “traditional” *(IgE-driven) allergies and (IgG) sensitivities, but also to non-protein substancesincluding chemicals like chlorine and fluoride, scents, hormones, exercise, temperature changes, pain, stress, sunlight and vibration to name a few. Yes, crazy making and challenging to live with!
And partly why the MCA diseases are so hard to recognize – they drive and/or mimic many other diseases and conditions, much like a chameleon. They’re hard to differentiate and properly diagnose for everybody.
Many people accidentally use the term MCAD to mean MCAS only, and many use the two terms interchangeably. (It doesn’t help they are off by only one letter on English keyboards either.) While technically incorrect, in the end, it’s the inappropriate mast cell over-activation in all cases that is aggravating us and sending us to the doctor (no matter how many mast cells we have and in what shape) so I don’t get too worked up about it. Just be sure to rule out mastocytosis and leukemia when appropriate. And do not use mastocytosis as the umbrella term any more.
(I was pleased to see the Mastocytosis Society actually change their name to The Mast Cell Disease Society for this very reason in 2020, thank you!)
Anaphylaxis comes in grades by the way, though doctors and EMTs are usually only interested or concerned with the highest levels/throat closing signs since that’s when it can kill you, and is what your school nurses are constantly watching for. Knowing the milder signs/levels can help you stay calm and medicate in time (or get away from a trigger) to help avoid it escalating to that level. (Staying calm really helps.)
No two people will have the same course of symptoms when reacting either. Some also react slower than others – we call ourselves “lucky leakers”, vs shockers. Finding this info useful? I can really use your support at any level here, TY!
So When to Suspect It?
This is accordingly really tricky, as truly no two patients even with the same form will present alike, even in the same family. As we say about some other conditions, it’s truly as individual as fingerprints just like EDS. Thus it is extremely widely varying in nature of onset, course, and response to medications as the brilliant US hematologist Dr. Lawrence Afrin depicts so thoroughly in his new book Never Bet Against Occam (Amazon 2016). (Highly recommended for both patients and doctors to read – both will find it validating in different ways.)
However, there are some common “themes” and experiences I am listing here, noting that this list is by no means official, nor comprehensive, no two patients will experience all of these issues, but most will experience a good handful if I’m on the right track. (This list is not officially endorsed by anyone yet.) Again, use this as a starting point for suspecting a form of MCAD with your doctor.
And yes, it highly resemblesHistamine Intolerance, which is a flip-side of the same coin: failure to out-process (metabolize and degrade) histamine leading to the signs of excess, vs over-production of histamine from over-activation.
And yes, some poor souls may even have both, along with methylation issueslending to even higher histamine levels in the body. (Try to keep your histamine levels down, both by not adding any from high histamine foods, avoiding triggers – so you don’t produce your own, and making sure you out-process what you do have okay.)
I’m increasingly convinced MCAD-driven inflammation probably underlies a large percentage of ER cases that are diagnosed as “just anxiety” or panic attacks, or angina and heart attacks that show no signs of heart disease. (Do play it safe and get yourself checked out if suspect any heart problem!) Hopefully this list will help folks to know when to suspect it:
Easy flushing darker or red, particularly of the “mantle” (upper chest, neck and face, not always 100%), and especially to stress, heat or triggers (including emotional)
Hives, especially stress-driven ones, can be large or small and not always all over
Urticaria Pigmentosa (persistent hives or bumpy “freckles” that fade but never disappear, and itch during reactions), TMEP, Purpura
Dermatographism – aka “skin writing” where you either turn dark or red easily or even get a hive-like welt (wheal) with a light skin scratch. (Google it for images.) You may notice (darker or red) indented sock & underwear “tattoos” where the elastic rests on your skin in winter
Adult onset or flare-ups of acne
Sudden onset diarrhea especially alternating with constipation (often called IBS)
Sudden abdominal bloating and swelling (can look “pregnant” when you’re not)
Sudden onset of gas and belching
Sudden onset nausea, trouble swallowing (rule out comorbid HDCT driven neurological drivers of this), early satiety
Tendency to run cold (but can alternate with sudden hot flashes/sweating bouts or run hot also)
React easily (are sensitive) to sunlight, vibration, startling, pressure, stress, hot or cold
Sensitive to alcohol and molds (the penicillin class of anti-biotics, mushrooms)
Reaction to bee stings and iodine contrast dyes, local & general anesthesia
Itching of unknown origin, may migrate, often severe
Tingling or burning sensation anywhere in the mouth or GI tract (BMS)
Tinnitus of all kinds, but especially after eating certain things
Variable blood pressure (BP), may run quite high or low on average and can swing widely at times. Some have a spike with anaphylactic reactions, followed by later drop.
Angio-edema (swelling) especially that “migrates”, e.g., shows up in different places (lips, eyes, hands, feet), not always in the same place nor due to being upright (gravity-driven)
Shortness of breath and asthma like symptoms and outright asthma
A persistent non-productive but wet-sounding cough with no identifiable infectious origin
Chronic post-nasal drip or rhinitis in the absence of allergies
Watery eyes, burning eyes (feeling of granularity or sandiness behind eyelids)
Rashes of unknown origin, adult onset acne or acne-like spots (not same as Urticaria Pigmentosa which is a form of cutaneous mastocytosis)
Easy nose-bleeds (epistaxis) of unknown origin, easy bruising or bleeding (w or w/o a comorbid connective tissue disorder)
Sudden onset aphasia, or loss of words or speech, slurred speech or “word salad” and confusion that clears up after the reaction/stress subsides or with anti-histamines or mc stabilizers (be sure to rule out stroke! as well as epilepsy).
Any and all forms and levels of anaphylaxis which comes in grades. It’s also different/harder to quantify under anesthesia as noted here.) Many are in mild constant low level state with occasional spikes to higher states or rebound events. (Most medical personnel refuse to call it anaphylaxis until it’s the higher level/s however be prepared for some differences of opinion here and try to stay calm and keep your epi and Benadryl handy.)
Sensitivities or anaphylaxis to any and all drugs, fillers, dyes, additives, preservatives, fluoride, chlorine, etc. We can react to any degree to almost anything, truly. (Yes, crazy making for all.) Sometimes it’s not the active ingredient, but a dye or filler. Or the fact you were upset when you ingested it.
Chronic fatigue, sometimes severe, often identical in onset/nature to opioid-induced respiratory depression (many find this in reaction to gluten and dairy) often misdiagnosed with Chronic Fatigue Syndrome
Pre-syncope – or dizziness, light-headedness, feeling about to faint (but you don’t)
Full syncope – full fainting (less common but also happens)
Clotting or alternatively bleeding disorders (either direction) that defy normal hematological diagnosis and workup (and treatment)
Swollen lymph nodes of unknown origin, not true lymphomas
Any other forms of hematologic disorders (strange cell counts/sizes, changes in same) that do not strictly match true workup for similar conditions (e.g. polycythemia in absence of the JAK2 mutation) or don’t respond appropriately to treatment for same
Migraines and cluster headaches, hydrocephalus and “corking” driven dysautonomia
Low blood volume from 3rd spacing and urinating more than ingesting during reactions (lends to BP drops and very low BP)
Interstitial Cystitis (IC) or chronic UTI’s that don’t resolve easily or at all with anti-biotics (i.e. “sterile” inflammation)
Women may notice “flares” of these symptoms on a monthly basis from their cycles, and or during lifetime hormonal changes, especially any time after age 30 from peri-menopause
Again, this list is neither official, nor comprehensive, but is a start for when to suspect these very tricky to diagnose Mast Cell Activation Diseases.
A very large dose of patience is in order – very few doctors are up on the the prevalence of the conditions yet even in May 2016 – nor know how to diagnose (very tricky,no single easy test for all) and how to treat (equally tricky: no single easy medication course works for all, and you may react to any and everything including known helpful medications for others – always start low and slow until you know).
Generally avoiding stress and high histamine foods (leftovers, ground meats, fish) and taking anti-histamines seems to be helpful on the whole.
Please be very patient, try to log and track triggers for yourself (and then avoid them as able), be mindful of your mood, condition and environment (including temperature and scents) at all times (I can eat chicken when calm but not when stressed or rushed, e.g.).
Try to eat single ingredients and whole foods vs complex or processed meals to reduce potential triggers and maintain best nutrition. (Some will fare better than others, some even react just to the physical act of eating, laughing, sex, travel etc. – yes, crazy-making as previously stated!)
Common comorbidities include heritable connective tissue diseases (especially some forms of Ehlers-Danlos Syndrome, notably the more common hypermobile type or a Hypermobility Spectrum Disorder), Fibromyalgia (often misdiagnosed hEDS or HSD in milder form), migraine, high cholesterol (increasingly recognized as a a sign of inflammation and not dietary driven), diabetes, auto-immune diseases of all kinds, CVID and all forms of primary immunodeficiencies (tendency to get sick easily and often), UTI’s, IC, easy bleeding (in absence of von Willebrands) and bruising, APABS (anti-phospholipid anti-body syndrome) and much more.
I’d like to suggest the chameleon as our official mascot: I’m starting to appreciate just how many diseases MCAD both mimics, and drives while going unrecognized for what it truly is.
I will add to this list as able. Again, it’s not meant to be comprehensive nor official yet, just suggestive. Consult a savvy* allergist to start, followed by a hematologist who is aware of MCAS as well as Mastocytosis if needed later. (*Not all allergists are aware of – nor believe in – MCAS yet, alas. You might join TMS to find a local support group to help you find the best doctors near you.)
See my MCAD Resources page for help with educating yourself and your doctors on the matter and consider joining The Mast Cell Diseases Society (now free!) for additional information and support for all forms of MCAD on and off line. Good luck! Last updated August 2022.