Friday, July 6, 2012

On the Threshold of...

AllergyMoms reposted this week about the SLIT interview Gina Clowes did with Dr. Demetrios Theodoropoulos from Associated Allergists of LaCrosse. It's an interesting interview. You should read it. 

SLIT is something that has a lot of history in Europe, particularly for environmental allergens, and there has been some compelling research about the sublingual area being a better way to introduce proteins for tolerance induction.

The main criticism (or strength, depending on your viewpoint) of SLIT is that it generally uses very small amounts of protein for desensitization. The thought process behind it seems to be almost homeopathic  that somehow a greatly diluted poison will cure an ill. In this case, the theory seems to be that the immune system has to "get used" to the protein, and can do so through very small exposures.

Two SLIT studies, both published this year, show an interesting contrast. The first found that, after therapy, only one of the kids in the SLIT group passed a challenge.

A different study shows much more promising results  after 12 months of SLIT therapy with just 2mg of protein, kids were able to eat an average of 1710mg of peanut. That's about 5-6 peanuts  the same result as the oral immunotherapy approach, but with far fewer side effects. (The abstract for this study, however, does not indicate how many of the 18 reached this level or whether a food challenge was required to get into the study, and both of these studies involves only a handful of children.)

I've read about SLIT for years. Our allergist does not support it; my husband and I are on the fence. When FAHF-2 came along, it seemed a better bet. 

SLIT is not really what the column is about, though. As usual, what I'm interested in is the psychology of the response to this therapy. Even the headline for the AllergyMoms article — "Why Doesn't Everyone Know About This" — underlines my point: many of the same mothers who make a religion out of scrupulously avoiding every. last. particle of protein are the ones who are now embracing the miracle cure. Isn't SLIT essentially the same as eating "may contain" food? Yes, I know, varying vs. consistent dose, medical supervision vs. DIY — but still!

Which brings us to threshold.

Each kid has a threshold level at which they will react to peanut. We know thresholds change with age, other stressers on the immune system, illness, hormones, even the amount of fat in the food that contains the peanut protein. However, if these things are all constant, a child's reaction to peanut will also stay relatively constant. 

Consider clinical trial challenges. The whole point of the FAHF-2 trial we're in right now is to feed my son peanut at the beginning and end and see if his response changes. If food allergy reactions were really dramatically unpredictable, this methodology would not work. Based on the FAHF-2 study, my son's current threshold seems to be somewhere between half a peanut and three peanuts. The researchers indicated this was a pretty typical threshold. 

More or less. Depends on
the peanut you weigh.
However, a sub-population of peanut allergic have a very low threshold. According to this studyabout 1% of the allergic population reacts to micro doses of less than 2mg. Another 16-18% will react to less than 65mg.

So my kid (and probably your kid) are in the other 80% of kids — the ones that typically don't react without eating overt peanut. Here's what one doctor had to say about this:

The benefits of a strict avoidance diet seem limited: reactions to the low doses and to the peanut oil refined are rare and most often slight. It is not proven that a strict avoidance facilitates the cure of allergy. On the other hand, strict avoidance could induce a worsening of allergy, with deterioration of quality of life, creation of food neophobia. In case of cure of allergy, it is difficult to normalize the diet after a strict avoidance. Outside of the rare sensitive patients to a very low dose of peanut, for which a strict avoidance is counseled, the report benefits risk is in favor of the prescription of adapted avoidance to the eliciting dose. For the majority of the peanut allergic children, it seems to us that the avoidance can and must be limited to the non hidden peanut.  

Arch Pediatr. 2006 Jul 5, Feuillet-Dassonval C, Agne PS, Rance F, Bidat E. 
Which avoidance for peanut allergic children?

I'm not as cavalier as these guys, and I'm certainly not counseling you to run right out and start feeding your kid "may contain" foods! It's important to remember that thresholds can change over time, especially at adolescence. 

On the other hand, if you have a micro-reactor, you probably already know it. These are the kids who react to the trace amounts on toys, or get the full-out reactions from kisses on the cheek, or who have had a known reaction to trace ingredients. Let's face it since cross-contamination labeling is voluntary, we don't know what's in our food. That means people with these levels of allergy are going to have reactions. A history of serious, mystery reactions is a good indicator you're dealing with a low-threshold child.

What I do hope is that this blog post can reduce some of the anxiety around peanut allergy. There are too many people who think of reactions as completely, wildly unpredictable and even the smallest amount of peanut as life-threatening. That's not an easy (or healthy) way to live! Understanding where your child is on the threshold continuum will hopefully help you put the risk in perspective.


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