15 Things You Need to Know About Mast Cell Disorders

1) Mast cells are found throughout the body, so symptoms can be anywhere. The same goes for connective tissue with the commonly comorbid Ehler Danlos. This means your symptoms may be digestive issues you’ve been calling IBS, your cousin’s may include a rash from sunlight and some unpredictable responses to medications, your friend may have “traditional” anaphylaxis with respiratory symptoms, your child may have “idiopathic panic attacks,” and others you meet may have any number of neurological, cardiac, or other complications or oddities you wouldn’t assume could be attributed to the same cause. This is one reason proper diagnosis can be such a challenge.

2) Mast cell triggers can be anything—scents, temperature or pressure changes, body products, hormonal shifts, electromagnetic fields, vaccines, surgeries, strong emotions, chemicals, things you touch, lack of sleep, vibration, foods, pregnancy, dental work, your own sweat...you get the picture.

3) It’s not about anaphylaxis.
In fact, many mast cell patients never experience anaphylaxis. Also, unfortunately, many are unaware they’re experiencing anaphylaxis because they think anaphylaxis=closed airways.

An absence of anaphylactic emergencies does not mean inappropriate mast cell activity isn’t causing long-term damage. This is why identifying triggers and finding proper treatment is important even for patients suffering from symptoms they can “live with.”

4) Many mast cell patients have been through the wringer, compiling a laundry list of diagnoses before finding one (or two, or three, in the case of the trifecta) which offer a more complete picture. Just a handful of the more common early diagnoses of people who are later diagnosed with a mast cell disorder: MS and other neurological conditions, lupus, fibromyalgia, urticaria (hives), angioedema, IBS, panic attacks, eating disorders, acid reflux/GERD, gastroparesis, vocal fold dysfunction, PANS, eczema and other dermatologic conditions, crohn’s, anxiety, colitis, idiopathic anaphylaxis, CIRS, asthma, oral allergy syndrome, IC, chronic bladder infections, and so on.

5) Mast cell reactions are not the same as allergies. They can, of course, look like allergies, ranging from mildly annoying to life-threatening anaphylaxis and organ failure, and both are treated in many emergency cases with epinephrine, but additional emergency treatment and prevention of these attacks is very different if the cause is a mast cell disorder versus an allergy.

Allergies can be diagnosed by blood tests, and avoidance of the allergen will prevent symptoms. Mast cell triggers, on the other hand, can change without warning (even day to day), and there is no test to identify them.

6) True allergies can be ruled out reliably by blood tests, but skin/patch/injectable testing for allergies is contraindicated if a mast cell disorder is suspected, because:

A) This testing can be extremely dangerous for mast cell patients, causing unexpected systemic reactions which often lead to long-term “flares,” and
B) This testing is also extremely inaccurate for this population. Mast cells cause inappropriate reactions to the needle prick or scratch testing, so totally different results can even be seen if the test is repeated twice in a single day.

Blood tests to identify allergens (which, again, are not the same as mast cell triggers) are both accurate and safe. Skin/patch/injectable testing for allergens or sensitivities, being neither, are the only tests which, even with precautions, should never be ordered for a mast cell patient due to their offering NO potential diagnostic benefit and all risk.

It follows, of course, that
suspected mast cell patients should never be advised to stop antihistamines for testing. This is repeated often in literature, interviews with specialists, and educational materials of all kinds, but many new patients miss these warnings. Antihistamines work downstream of the mast cell mediators we are able to test, so they do not impact results, and the only test they do affect is skin testing. So, if an allergist, or any practitioner, advises you to stop treatment with antihistamines before a test, this is a good indication that you’re about to have a skin test, and either a) your practitioner is wholly unfamiliar with mast cell disorders or b) your practitioner does not believe you could possibly have a mast cell disorder. Assuming you’re here because you have reason to suspect one, either of these means you need to find a new practitioner.

In general, allergists and immunologists are not the first port of call for mast cell disorders. The majority of mast cell specialists are hematologists and others with a particular focus on the “trifecta” of commonly comorbid conditions (MCAS, Ehler Danlos, and POTS). Keep in mind that, while most hematologists and oncologists are familiar with mastocytosis, fewer know MCAS.
Most patients will never to see an actual mast cell specialist, but they will need their current providers to become familiar with these disorders or to find another competent prescribing provider who is. See Finding a Medical Provider.

7) Mast cell disorder patients are often the “I didn’t know that could happen” patients.
A premedication protocol is recommended before any radiology procedure. Even without the administration of contrast agents or dyes (good things for most mast cell patients to avoid), these procedures are common triggers due to radiation, electromagnetic fields, and other factors. Many patients are advised to follow the same or a similar protocol for any surgeries, dental work, and so on. An emergency protocol with a note about premedication is available here.

8) Though a “newer” diagnosis which is commonly missed, MCAS is far more common than any form of systemic mastocytosis, and more "serious" mast cell disorder cases arise from MCAS than from SM. However, my estimation is that about 90% of patients with MCAS have at some point been told by their practitioners to suspect systemic mastocytosis, instead, solely because their provider knew what mastocytosis was. This confusion isn't as big of an issue clinically; with the exception of mast cell leukemia (which is included in the WHO’s systemic mastocytosis list but is considered a general population risk rather than a mast cell disorder population-specific risk and so is not covered on this website), there is no across the board difference in treatment between MCAS and systemic mastocytosis patients, because

9) Treatment is very individual. There is no way to predict in any given patient which H1 and H2 antagonists will be most effective, and there are a number of other classes of drugs, supplements, lifestyle changes, alternative therapies, and so on which might be right for one case and very wrong for another, even when these cases present with very similar symptoms or triggers.

10) For MCAS, our testing is, at present, woefully inadequate. (SM is much easier.) We know that there are at least over 300 mediators released during mast cell degranulation and that different patients are affected by different ones, but we can only test about ten percent of these currently in blood, 24 hour chilled urine, and spot urine. To make matters worse, very few labs are equipped to handle these specimens properly, and even when this is assured, many patients go through several rounds of “false negatives.” There’s also currently no test to “rule out” MCAS, and it’s often treated (as are a number of other complex conditions) as a diagnosis of exclusion. Since laboratory confirmation is often unavailable, many patients on successful treatment for their mast cell disorder only meet two of the three generally recognized diagnostic criteria: symptoms indicating the presence of a mast cell disorder (having ruled out other causes) and positive response to treatment.

11) Baseline treatment for a mast cell disorder
(whether an overproduction of mast cells, as in the case of systemic mastocytosis, or mast cells behaving badly, as in the case of MCAS) consists of typically non-sedating H1 antagonists (cetirizine-Zyrtec, loratidine-Claritin, desloratadine-Clarinex, levocetirizine-Xylal, fexofenadine-Allegra) taken at the same times as H2 antagonists (famotidine-Pepcid, nizatidine-Axid, ranitidine-Zantac, cimetidine-Tagamet) at regular intervals throughout the day. Since it’s impossible to predict which will be best for a particular patient, the usual recommendation is to begin trials of each combination every 12 hours, though some recommend starting at every 8. Many patients find one or two combinations of the above make a significant difference in their symptoms, while others do nothing for them. These drugs are readily available in most countries over the counter, so it’s possible and typically recommended to start treatment trials on your own, but...

12) Many mast cell disorder patients need their medicines compounded with particular fillers because excipient (dyes, fillers, binders, flavors, coatings, etc.) reactions are extremely common. It is very typical for patients to believe they are allergic to or have unexpected responses to a number of well-tolerated medicines only to discover they are in fact reacting to an excipient rather than to the drug itself.

13) Support groups are a wonderful resource, but in some cases, recommendations received here can be problematic
in part because so many people mistake other (also difficult to diagnose, complicated) conditions for mast cell disorders. See this page. You are likely to meet a number of people who believe they have “cured” their mast cell disorder, for example, often without any recognized treatment. This is, of course, great news for them, but these people very likely cured something quite different (histamine or gluten intolerance, shellfish and other allergies—by not eating these things—anxiety about various dermatologic conditions, infections whose symptoms were mistaken for a mast cell disorder, and so on), and in many cases did not know these things:

A) Histamine intolerance is not a mast cell disorder. While many high histamine foods are common mast cell degranulators and otherwise triggers (which understandably adds to this confusion; some foods and drinks commonly cause problems for both groups) and many with mast cell disorders also have to limit excessive histamine intake, these conditions are very different. Histamine and other amines from dietary sources are not coming from mast cell degranulation, and their not being broken down properly, while it adds to this burden, does not indicate anything wrong with mast cells themselves either in number or function. After being referred to these repeatedly, I discovered a couple popular pages on which MCAS (and sometimes mastocytosis) and histamine intolerance are conflated, resulting in many new patients believing they have a mast cell disorder but subsequently curing themselves by treating histamine intolerance (either by avoiding high histamine foods or by supplementing with DAO, which is the digestive enzyme histamine intolerance patients do not adequately produce). There is simple testing available to identify histamine intolerance/inadequate DAO production, and this offers a (comparatively) simple fix.

B) The presence of mast cells in skin, bone marrow, and organs is normal.
You’ll likely meet many people who have had biopsies of various kinds identifying normal quantities of mast cells who mistakenly believe they have mastocytosis. (This might be another reason “mastocytosis” is so common in support groups even though MCAS is so much more common clinically. This may also help explain why so many who identify as mastocytosis patients in these groups don't respond to mast cell treatment, improve dramatically without any recognized treatment, and seem to tolerate some of the most commonly dangerous mast cell triggers.)

This isn’t to say that patients can’t have histamine intolerance AND a mast cell disorder, the same way it’s possible to have celiac, allergies, hereditary alpha tryptasemia (which causes high tryptase, just like about 80% of mastocytosis patients—but only 15% of MCAS patients—have), a tooth infection, the flu, appendicitis, AND a mast cell disorder.

14) Cutaneous mastocytosis is a different circus.
Many babies and toddlers are diagnosed with CM’s characteristic “spots” via biopsy. These may or may not progress to systemic symptoms, and while most are advised to follow certain basic precautions, a diagnosis of CM is fairly common among babies and toddlers. If you own a small, spotted human, try not to panic.

15) As a patient or as a caregiver, it’s easy to get discouraged both by inadequate medical support and the various challenges and unpredictable nature of living with a mast cell disorder. As in the case of many other conditions without cures, treatment is available for any form of MCAD. Don’t give up.

And a 2020's bonus: Very early on, it was evident that many cases of Post-Covid-19 Syndrome were difficult to distinguish from the mast cell dysfunction which characterizes MCAS, and the virus is now a widely-recognized potential trigger (of which there are many) for MCAS. Many "post-Covid" patients respond to mast cell treatment.