MCAD, MCAS and the hierarchy of mast cell disease classifications
I have seen several posts recently expressing confusion about various mast cell diagnoses so I figured I would put up a post to clear things up.
Mast cell activation disorder (MCAD) is a catch-all term for mast cell disease (MCD.) MCAD and MCD can be used interchangeably. So if you have any mast cell disease, you have MCAD. If you have SM, you have MCAD, because SM is a type of MCAD. If you have UP, you have MCAD, and so on. MCAD is an umbrella term. It is non-specific. It is similar to being told that you have heart disease when you have mitral valve prolapse. It is true, but it is not precise enough to give all information needed to treat effectively.
Mast cell activation syndrome (MCAS) is the diagnosis you get if you do not meet the criteria for any of the defined mast cell diseases, but have mast cell mediator related symptoms. You cannot have MCAS and another mast cell disease because, by its definition, MCAS is ONLY diagnosed if you do NOT meet the criteria for any other mast cell disease. You cannot have UP and MCAS. You cannot have SM and MCAS. I think some people think that MCAS means you have mediator related symptoms. This is not the case. You can have mediator related symptoms with pretty much any mast cell disease.
A paper was published a few years ago by a doctor who considers mast cell activation symptoms to be due exclusively to proliferation (like in SM.) He wrote a paper that says that MCAS is found in people with SM. This paper sort of confused the issue for a lot of people. However, the mast cell community (including researchers and prominent doctors) do not consider this to be the case. They agree that you cannot have SM and MCAS.
Also confusing is the fact that mast cell activation (MCA) is NOT the same as MCAS. MCA just means that your mast cells are activated, which occurs in any mast cell disease. MCA is not a diagnosis, it is a symptom. So you can have MCA in SM. But you still can’t have MCAS in SM.
So if you have SM and have lots of mediator related symptoms, you have SM. If you want to speak broadly, you have SM.
If you test negative for SM and have no CM, but have mast cell symptoms and elevated mast cell markers, you have MCAS.
If you have UP and then later develop SM, you have SM with skin involvement, or SM with UP.
If you have UP or TMEP and have lots of mediator related systemic symptoms, you do NOT have UP and MCAS. You have UP. UP and TMEP (forms of CM) can cause systemic symptoms. But you cannot have MCAS because you can only have MCAS if you do not meet the criteria for another mast cell disease.
If you have UP: you have UP, you have CM, you have MCAD.
If you have TMEP: you have TMEP, you have CM, you have MCAD.
If you have SM: you have SM, you have MCAD.
If you have SM with UP: you have SM with skin involvement, you have UP, you have MCAD.
If you have SM with TMEP: you have SM with skin involvement, you have TMEP, you have MCAD.
If you have SM-AHNMD: you have SM-AHNMD, you have MCAD.
If you have ASM: you have ASM, you have MCAD.
If you have MCL: you have MCL, you have MCAD.
If you have MCAS: you have MCAD.
Molderings GJ, Brettner S, Homann J, Afrin LB. Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. J. Hematol. Oncol.2011; 4:10-17.