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 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 instead of 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) As above, 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 also happens to be 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 a 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. So, if an allergist, or any practitioner, advises you to stop antihistamines before a test, this is a good indication that you’re about to have a skin or other exposure allergy 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 need 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 many 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 is. This confusion isn't as significant of a problem 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.

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 currently, we can only test a tiny fraction of these 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” because these mediators degrade almost immediately. 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. See this page. A few sources of this confusion are:

A) Histamine intolerance is not a mast cell disorder.

B) The presence of mast cells in skin, bone marrow, and organs is normal.

C) Many other conditions can be mistaken for a mast cell disorder. See this list.

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 by the various challenges and unpredictable nature of living with a mast cell disorder. As in the case of many other conditions without simple "cures," treatment is available for MCAS and every form of SM. 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 very favorably to mast cell treatment.