HIT v MCAD

I often get asked on my blog what the difference is between Histamine Intolerance and Mast Cell Activation Syndrome, whether there is any link between the two and how to tell if you have one or the other (or like me, both!).   The answer is we know very little about Histamine Intolerance, and not a whole lot more about MCAS, and virtually zero about the two conditions in tandem.

I have no medical qualifications and am not an expert in either disease, so I can only write about my own experience and what I was told by the Consultant who diagnosed me (arguably the UK’s leading expert on both conditions).  Knowledge is an ever changing thing and what I know now may obviously change in the future as more is discovered about my little understood diseases.

I’m as certain as I can be that I was born with Mast Cell Disease.  I have photos of myself as a very young child where I am flushed bright red and my Mum tells me I was dermographic from a tiny baby.  She didn’t think much of it, however, as she was dermographic and got wheals and hives from tight clothing so she thought it was normal, just as she thought my “double jointedness” was normal and my velvety elastic skin was normal because she too was hypermobile and had stretchy skin.  As far as I’m concerned my MCAD is hereditary and genetic.

Photo of mast cell induced flushing

Flushing as a 3 year old child.

As most of you know, people with Ehlers-Danlos Syndrome are massively more at risk of MCAD than the healthy population but quite why is still a mystery.  There are several theories but they are just that – theories.  The truth is no-one knows.  We also don’t know if MCAD causes EDS, if EDS causes MCAD or if neither causes either and there is another mechanism at play altogether.

My mast cells are activated by all manner of things which the mast cells in a healthy person would rightfully ignore.  Heat, hot water ( very itchy!), cold, cold water (ouch and double ouch!), stress, hormones, some pollens, alcohol, some animals, emotions (particularly excitement), strong winds, exercise, just about all drugs and a host of other situations cause my mast cells to lose the plot, leading from mild problems like nausea or feeling fluey to full blown anaphylaxis and everything inbetween.  But until the age of 44 I could eat whatever I liked and I loved my food.  For the decade I was bedridden with severe M.E., and could do virtually nothing but stare at the ceiling all day, food was my biggest pleasure and I looked forward to mealtimes like an oasis in a burning desert.

Everything changed one day when I was 44 and suddenly started passing out every time I ate.  This was the start of what I discovered was Histamine Intolerance and for me it felt totally separate to my MCAD.  Very little is know about HIT but it’s thought to be caused by a lack of, or badly functioning, enzymes called Diamine Oxidase (DAO) and/or Histamine N-methyltransferase (HNMT).  My HIT was brought under control in about 6 months purely from changing to a low histamine diet, but it’s not ‘cured’.  I still have to maintain a low histamine diet otherwise my symptoms start to creep back and very soon I’m reacting again to everything I put in my mouth (histamine is part of the digestive process for everyone but my poorly enzymes can’t effectively deal with it, so it’s vital I keep my ingested histamine to a minimum).

So, for me, there are some vital differences between my MCAD and my HIT:

  • HIT is only related to what I eat or drink.  MCAD is related to my wider environment, both external (eg pollen) and internal (eg emotions).
  • HIT developed in middle age.  MCAD has been there since birth.
  • HIT causes anaphylaxis-type symptoms only (eg drop in blood pressure, palpitations, nausea, vomiting, fainting, flushing).  MCAD too causes anaphylaxis but also other symptoms (eg itching, dermographia, hives, swelling, sneezing, migraine, pain).
  • The symptoms from my HIT subside within 2 hours of eating.  The symptoms from a mast cell flare can last days, weeks even months – mast cell activation perpetuating mast cell activation and causing a neverending vicious circle.

As far as I know no link has been established between HIT and MCAD.  None of the major papers written by world experts on mast cell disease mention HIT as part of the puzzle which, if HIT were a major cause or perpetuating factor of mast cell degranulation, you would think they would.  I’m not saying the two aren’t connected because I have no clue, but for me they feel like very separate entities and my Consultant diagnoses them as two distinct and separate diseases.  That they both involve histamine is intriguing (though the mechanisms are vastly different), but we have no idea if people with MCAD have a higher incidence of HIT than the general population because no data on this exists.  It may just be coincidence if you have both diseases or it may not.  It may be that mast cells degranulate as part of HIT or it may not (I suspect not but that’s just based on my own experience).

When I’m having a mast cell flare, my HIT does appear to worsen.  However, I personally don’t think this proves a causal link.  What I suspect is happening is that my mast cells are producing excess histamine which my body is already struggling to cope with, so when I eat and even more histamine is produced from the act of digestion it causes overload and I get symptoms after eating that I wouldn’t get if my mast cells were behaving themselves.  So food/digestion isn’t causing mast cell degranulation, which is already happening from other causes, it’s just adding to my body’s histamine excess.  I may, however, be totally wrong.  No-one knows what’s happening yet and it’s not an area anyone is researching as far as I’m aware.

There are sites online which appear to contain authoritative and convincing information linking HIT and MCAD but I can find no research, and therefore facts, on the two conditions and none of the articles I’ve read contain links to research papers.  So as far as I’m concerned information linking the two diseases is based on nothing but speculation and guesswork and you all know how I feel about that 😉

So, that’s my take on HIT and MCAD but of course my experience may be different to yours.  According to my Consultant, you can have MCAD without HIT, you can have HIT without MCAD but you can also, of course, have both.

 

 

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