Monoclonal Mast Cell Activation Syndrome (MMAS)?

The Disease / Saturday, April 22nd, 2017 / no comments

You have probably heard of mastocytosis and MCAS, but have you heard of MMAS?

MMAS stands for “monoclonal mast cell activation syndrome”.

I believed this may actually be the type of mast cell activation disease I have, looking back at my test results and then comparing them to what the experts are saying:

Some patients with recurrent mast cell activation may have clonal mast cells in bone marrow as in mastocytosis (systemic or cutaneous) or a monoclonal mast cell activation (MMAS). Patients with clonal mast cell disorders generally have varying degrees of expansion of the mast cell compartment derived from a progenitor with a genetic defect that presumably reduces the cell’s threshold for activation. These patients may have elevated serum tryptase levels, carry c-kit mutations (most commonly D816V) in lesional mast cells, or have other markers of mast cell clonality such as aberrant CD25 expression.

And again:

MMAS has been diagnosed in patients with systemic reactions to hymenoptera stings and elevated baseline serum tryptase as well as in patients with unexplained episodes of anaphylaxis. A bone marrow biopsy establishes the diagnosis by revealing the presence of monoclonal mast cells that carry the D816V KIT mutation and/or express CD25 while the diagnostic requirements for systemic mastocytosis are not met.

I had systemic reactions to wasp stings (each one worse than the last) when I was stung three different times in less than  a year back in 2014/15. I am c-kit negative (both blood and bone marrow tested) and there were no multifocal dense infiltrates of mast cells, but according to my BMB results I do fulfill one of the minor criteria for diagnosing mastocytosis because at least some of my mast cells are expressing CD25.

My main concern is whether or not MMAS is “borderline mastocytosis” and I can’t help but wonder, am I in the very early stages of mastocytosis??

I asked my doctor and he honestly didn’t know. The experts thankfully address this question here, though:

While one might speculate that MMAS may simply be a precursor to systemic mastocytosis, several lines of evidence suggest that this is not the case. First, follow up data available so far do not indicate progression to systemic mastocytosis in most patients with MMAS. Second, not all patients with systemic mastocytosis go through a phase with mast cell activation symptoms before developing signs or symptoms of tissue mast cell expansion.

Whew! Reading that makes me feel a lot better.

I guess at this point I don’t need to worry too much about narrowing down a specific form of MCAD since the medicines are working (hallelujah!) and I’m not getting any worse now. Both my doctor and my insurer are satisfied with my being diagnosed simply with “mast cell disease” so I suppose I should be happy with that diagnosis, too.

Of course I’d rather not have any form of it, but I’m no longer as worried as I was when I thought that my having (what appears to be) MMAS means it could be the early stages of mastocytosis.

Time will tell, of course, but my fingers are crossed that the experts are right about this one.


Mother. Wife. Patient. Keeper of Huskies. MCAS blogger & advocate. Living life in the mast lane with the Grand Tetons & Yellowstone as my backyard. You can also find me blogging at Life In The Mast Lane and The Empty Nest Housewife.

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