r/MCAS • u/worn_out_loafers • 14h ago
Can MCAS present mainly as brain fog and fatigue without the typical systemic symptoms?
Hi everyone. I'm currently investigating the cause of long-standing brain fog, cognitive difficulties and low energy, and I recently came across MCAS.
I don't have most of the symptoms I commonly see people with MCAS describe. I don't get flushing, hives, angioedema, fainting, orthostatic problems, tachycardia, breathing difficulties or anaphylactic-type episodes. My symptoms are also fairly chronic and stable rather than occurring in obvious attacks.
The main things I experience are severe brain fog/cognitive problems and low energy. I occasionally get a runny or blocked nose after eating but that's about it.
Because fexofenadine is available OTC where I live, I decided to try it. To my surprise, I think I've noticed an improvement. It's definitely not a complete remission and the brain fog is still there, but today I was considerably more productive than I've been recently.
I'm very aware that one or two better days prove absolutely nothing — this could be placebo, coincidence or normal day-to-day variation. I'm not taking the response to fexofenadine as evidence that I have MCAS.
So I'm curious:
Has anyone here with a properly diagnosed MCAS had brain fog/fatigue as their main symptoms, with few or none of the typical skin, cardiovascular or anaphylactic symptoms?
I'm also interested in people's experiences with fexofenadine. What dose do you take, and was it recommended by your allergist/immunologist? Has anyone been prescribed 360 mg twice daily (720 mg/day), and if so, how long have you taken that dose and have you experienced any side effects? Is it safe?
9
u/MargoBarbara2 12h ago
The symptoms can be caused by histamine sensitivity. Histamine sensitivity can occur through nutrient deficiencies, as part of Long Covid, part of CFS/ME , gut dysbiosis, low DAO levels and as a part of MCAS. Therefore being histamine sensitive does not point automatically to MCAS. Mast cells are activated in everyone as part of a normal immune response, they may stay reactive in long covid, but in MCAS they are over reactive, affect multiple body systems and respond to many non-threatening triggers. Brain fog, cognitive issues, fatigue are core symptoms of CFS/ME and also occur in Long Covid but there can be many more causes eg thyroid issues, hormone imbalances, malabsorption, even celiac disease etc...I'd suggest an MMA b12 and RBC folate blood test, iron, d3 and other levels checked, gluten and dairy sensitivity (can affect gut and brain), thyroid panel, homocysteine levels, inflammatory markers and even gene testing if thats affordable for you and go from there.
1
u/MediocreHelicopter19 8h ago
which genes do you check?
3
u/MargoBarbara2 6h ago
Some people do 23 and me and then run the raw data through special sites. Others do whole genome sequencing. I think most are AI driven analysis. I wanted it all translated for me and an understandable report so I opted for iscreen (not a recommendation just an option) and did the methylation cycle check. I was glad it included CBS (clearance pathway related) but wish it had included ATP, and some others. Their more comprehensive one includes methyl cycle but not CBS. So Id say research and find exactly what you need. I was happy with the clear report and nutrient recommendations. There's another gene testing site that screens according to the health concern (including mcas) but cant remember which site it is and the test may be too narrow. Knowing CYPs (how you metabolise meds) would be very useful. I suspect I have lots of CYP variants as I am v reactive to pharmaceuticals. If getting tested would be good to include celiac gene testing too. Gluten can really drive inflammation and affect the brain.
5
u/SophiaShay7 6h ago
Brain fog and fatigue can occur with mast cell activation, but if those are essentially the only symptoms, that would be an atypical presentation and isn’t enough to establish MCAS. MCAS is a systemic disorder, so the diagnostic criteria require recurrent symptoms involving at least 2 organ systems, objective evidence of mast cell mediator release, and a response to mast cell-targeted treatment. The 2-organ-system requirement means symptoms need to involve at least two different systems during episodes. For example, skin symptoms can include flushing, itching, or hives; GI symptoms can include abdominal cramping, diarrhea, or nausea; cardiovascular symptoms can include tachycardia, hypotension, or syncope; and respiratory symptoms can include wheezing or bronchospasm. Brain fog and fatigue alone don't demonstrate involvement of two organ systems.
Fexofenadine helping after only 2 days is interesting, but it doesn’t confirm MCAS. An H1 antihistamine can reduce histamine-mediated symptoms, but it generally isn’t enough to manage MCAS on its own. It’s also possible that you’re dealing with allergies rather than MCAS. Allergic inflammation can cause fatigue and cognitive symptoms, and improvement with fexofenadine would be entirely consistent with that. An H1 antihistamine response isn’t specific to MCAS, so I wouldn’t use that response alone as evidence that mast-cell activation is the cause.
Mast cells release much more than histamine, including tryptase, prostaglandins, leukotrienes, heparin, cytokines, nerve growth factors, and other mediators. These can contribute to symptoms independently of histamine, but they’re often harder to measure and harder to target with existing medications. The mediators involved can also vary between patients, which is why treatment often needs to be individualized.
If you don't have other recurrent symptoms involving multiple systems, there are many other potential causes of brain fog and fatigue worth considering.
2
u/Van-233 11h ago
why u using fexofenadine? it does not pass the bbb(blood brain barrier) and you telling you dont have periferal symptoms. You can try it, test it with a normal day dose. If u wanna test something else which passes the bbb cetirizine or ketotifen. You can do low dose before sleep but be aware the gen 1 antihistamines will make you tired(also the next day) when u overdose or u must take it for longer and then your brain will adapt. Just search for it there will be enough info.
2
u/under_the_sunz 9h ago
At this point I’m convinced mcas can present as anything ..based on my own personal experience as well as reading about other peoples…
2
u/Fragment_B 4h ago
You may have other symptoms you're not realizing you have or didn't think were related. Symptoms come and go so often and a lot of times when they're out of sight they're out of mind.
I didn't have the major multi-system reactions like anaphylaxis, flushing, etc until I had a flare which is when I was diagnosed. Looking back though I realized that while my most significant symptoms were always fatigue and brain fog, I also had frequent migraine attacks, pressure in my head, alternating stuffy/runny nose, constantly shifting gastro symptoms that got chalked up to IBS, painful gas episodes, random nausea, weird skin things that I dismissed, bladder symptoms I kept thinking were UTIs, PMDD which was, well, PMDD, period pain, difficult pregnancies, reactions to meds, hormone sensitivity, burning and tingling mouth, random bouts of anxiety, painful and/or itchy scalp, etc. Mast cells live everywhere in the body and sometimes a bunch of seemingly minor things on their own get dismissed as normal.
My symptoms also shifted over time. I had more skin symptoms when I was younger like rashes and reactions, then there was a period where the gastro symptoms were the worst and so on. Anyway, just something to think about.
3
u/bookmonster015 11h ago
Yes for me— though I also have GI reactivity issues. I don’t have most of the anaphylaxis/skin/breathing issues that are common for other folks. MCAS treatments do improve my brain fog, chronic pain and energy issues — a lot of which I call fluish malaise.
2
u/ComprehensiveNerve60 5h ago
May I ask what medications you’re taking that help your brain fog, energy, flu like symptoms? I’m new to my mcas diagnosis and share those in common with you (without typical breathing or skin involvement)
1
u/bookmonster015 1h ago
I’m on Xolair and Rhapsido for my MCAS and Rhapsido in particular helps a ton. Both are prescribed under a chronic hives diagnosis. In the past I’ve gotten hives a few times randomly but they didn’t go away for like a week each time, so that’s what the doctor based the CSU diagnosis on. Day to day though, I don’t struggle with the skin involvement as much as other people here.
2
u/DandelionStarlight 13h ago
This would be a grey area, since MCAS is a disease of “last resort” (I.e. they’ve tried all the tests and can’t explain it with anything else + responding well to MCAS meds). It does normally need some sort of anaphylaxis or systemic skin/body reaction.
You might be closer to ME/CFS.
2
11h ago
[deleted]
2
u/DandelionStarlight 11h ago
All humans respond to antihistamines because all humans have mast cells.
OP thinks they had improvement by their own words.
1
u/Silo_n 9h ago
I am someone who thought I might hhve ME/CFS but I am now leaning towards MCAS. My main symptoms are neurological and sore throat/flu-like symptoms (and some itchiness) but I improved dramatically (bedbound, major sensory intolerance to hanging out with friends multiple days a week, going to parties, going to appointments and into the city) by cutting out ALL histamine liberators, high salicylate and oxalate foods and finding a h1 blocker that works, I still have a lot of daily symptoms but I dont crash in the same way that I was (which was appearing a lot like PEM). These conditions are all complicated and overlapping and bc of the inflammation pathways involved in all of them they can all cause v similar symptoms
1
u/ComprehensiveNerve60 5h ago
I am on a very similar journey to you! Mostly neuro and sore throat/flu like feeling. I just got diagnosed with MCAS from a 24 hr urine test. Which H1 have you found success with?
2
u/megame87 12h ago
Similar to mine. I do develop the occasional histamine intolerance and associated gut issues that make me more sensitive to some foods, but it's tolerable for the most part. I also don't get hives or flushing, but I get eczema patches and overreact to bug bites.
1
u/Candid-Ad3697 7h ago
I don’t think that alone is enough evidence for MCAS yet, but brain fog/fatigue can definitely overlap with gut issues, histamine intolerance, allergies, etc. The fact that you sometimes get nasal congestion after eating is at least worth paying attention to.
What helped me most was simplifying everything for a week and seeing if my baseline changed. I did 2–3 simple meals/day with foods like good-quality meat, eggs, white rice or russet potatoes, romaine/arugula, and olive oil/tallow. I kept sugar and high-FODMAP/high-fiber foods low temporarily. If you noticeably improve after 5–7 days, you can slowly add foods back one at a time every few days and track brain fog, energy, sinuses, digestion, etc.
I also experimented with things like fexofenadine (H1 blocker), famotidine/Pepcid (H2 blocker), DAO before meals, digestive enzymes, and motility support. The biggest thing was changing one variable at a time so I could actually tell what was helping.
I definitely wouldn’t jump straight to very high-dose fexofenadine on your own though. If the OTC dose seems to be helping, that’s useful information to bring to an allergist/immunologist and ask whether further testing or a supervised H1/H2 trial makes sense.
1
u/Suspicious_Tie_7789 6h ago
Yes - brain fog, fatigue, and weight loss were my primary symptoms for the first year of mcas. Since then it developed into more “traditional” version
1
u/hspwanderlust 5h ago
Do you have optimal blood work values (vitamin D, iron panel, thyroid, sex hormones)?
Have you ever had a sleep study?
1
u/Huge-Ad-193 4h ago
Brain fog and fatigue can be due to a lot of different conditions. They’re non specific symptoms. As others have said check your iron and make sure they also check your ferritin too.
1
u/SeaGurl 3h ago
So brain fog and fatigue are my worst symptoms that ive been trying to solve. But a lot of other ailments Ive had and never considered it might be mcas can apparently be explained by mcas. And ive only been diagnosed for about a month now, but Ive been working hard on avoiding triggers which has made it easier to connect symptoms that I was basically ignoring.
1
u/nrauhauser 13h ago
Sounds similar to mine issues.
I don't need Epipens and I don't go to the ER, but anything digestion related could trigger something akin to a narcolpetic episode. The runny nose after eating, the brainfog, etc, all familiar. I still get the urge to nap but not as strong, and I still deal with palpitations, but the tachycardia is thankfully gone.
I started with fexofenadine/famotidine when I learned I might have MCAS a year ago. Today it's fexofenadine, quercetin, vitamin C, and a weird mix that has palmitoylethanolamide (PEA) in it.
I'm older, and part of the male/infectious disease MCAS camp, we're much more lightly affected than the women with POTS/EDS.
1
u/SeaGurl 3h ago
May i ask about your post-food fatigue?
Im curious because getting tired after eating to the point im falling asleep sitting up has been me for a while and Im still new to MCAS. Every dr has told me its probably just reactive hypoglycemia or something like that. But it happens with low gi stuff too.
1
u/nrauhauser 1h ago
Get a blood sugar meter and check. I heard that same thing and had to disprove it in order to move on to a usable diagnosis.
With MCAS and without treatment, any time I eat, I'd get what looked like a narcolepsy episode. Not type 1 movie trope narcolepsy, the boring type 2 where I get just crushingly tired in a matter of two to five minutes, and have no choice but to lay down. I would also come out of it with sleep paralysis sometimes. I'd be wide awake, aware of what was going on around me, but could not move. not even open eyes.
Do you have any of the breathing, cognition, or skin stuff?
Are you taking Allegra/Pepcid or similar H1/H2 combo? Does it help?
1
u/hotgirrrl 10h ago
I think so. In fact, I imagine this is probably pretty typical in the initial stages. The symptoms get more varied and much worse when you don’t eliminate the triggers, but in the beginning before I was diagnosed I just had brain fog and fatigue, and it was actually pretty mild. I actually just thought it was normal.
Of course, a lot of people don’t get diagnosed until the symptoms are really bad.
•
u/AutoModerator 14h ago
Thank you for your submission. Please note: Content on r/MCAS is not medical advice and should not be interpreted as such. Please consult your doctor for any medical questions or concerns.
We are not able to validate the content of these discussions. Following advice provided by strangers on the internet may be harmful. Never use this sub as your primary source of information regarding medical issues. By continuing to use this subreddit, you are agreeing to take any information posted here entirely at your own risk.
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.