Should the disease known as "Chronic Idiopathic Anaphylaxis" be re-termed, "Mast-Cell Activation Syndrome" (aka MCAS)? There have been several JACI articles that describe pts who have recurrent anaphylaxis but do not meet diagnostic criteria for Systemic Mastocytosis, so the authors propose that we categorize these pts as having "Mast Cell Activation Syndrom". Didn't we use to describe these same pts has having "Chronic Idiopathic Anaphylaxis"?


Are there any differences between Chronic Idiopathic Anaphylaxis and Mast-Cell Activation Syndrome?


Thank you for your recent inquiry.

Chronic idiopathic anaphylaxis differs from mast cell activation syndromes. There are a number of different point mutations on mast cells which enhance their growth and lower the threshold for degranulation. The most well known of these is the 816 V mutation on the c-kit receptor. This is of course a marker for systemic mastocytosis. However, there are other cases which are, for lack of a better term, forme fruste forms of mastocytosis which have some histologic markers for this condition, but lack all of the previously designated criteria to make a diagnosis of systemic mastocytosis. These patients can have lower thresholds for mast cell degranulation. Some cases originally thought to be idiopathic anaphylaxis are a form of this condition, just as some cases turn out to be mastocytosis. However, other cases of idiopathic anaphylaxis have no markers whatsoever of systemic mastocytosis on bone marrow biopsy, and these patients remain categorized as idiopathic anaphylaxis patients.

This is purely, as you can tell, a matter of semantics, and perhaps in the future, the terminology will change. But for now, in my opinion, this is the best way to view these conditions as far as their "labelings."

Thank you again for your inquiry and we hope this response is helpful to you.

Phil Lieberman, M.D.

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AAAAI - American Academy of Allergy Asthma & Immunology