“I am allergic to all nuts.”
A friend of my wife cornered me at a Christmas party this year and told me her story. Hearing such tales is an occupational hazard for physicians, but I usually take it in good humor and sometimes even learn something myself. She told the story of living through an anaphylactic episode at age 13 after eating a single cashew. As she was chewing it a burning painful itching sensation began suddenly on her tongue and spread to the back of her throat. Next she started itching all over, turned red, felt nauseated and weak, and started to have trouble breathing due to her very tight throat. She was rushed to the emergency room where she had several shots, an iv was placed, and after awhile she felt better and was allowed to go home. Her pediatrician told her and her family at that time to never allow her to eat nuts again.
“Am I really allergic to all nuts?”
She had been wondering whether the advice she was given was true, and she certainly was interested in trying some nuts if it would be safe. Many holiday recipes use nuts to flavor or garnish a dish. Some Christmas cookie recipes use a base of ground up nuts instead of flour. Oriental foods often have peanut or cashews. Mediterranean diets also emphasize nuts as a source of healthy fats and protein.
Cross reactivity is a term used in allergy that describes the body’s ability to have recognition of a food or airborne allergen due to an allergy to a different food or airborne allergen. For example people who are allergic to hickory tree pollen are also allergic to pecan tree pollen due to the similarity of the pollen. People who are allergic to cow’s milk can also be allergic to goat’s milk in some cases. With nuts the case is trickier. Studies of peanut allergic patients have noticed that almost half of them develop allergies to tree nuts. However there seems to be no cross reactivity between tree nuts and peanuts so this represents the development of a new food allergy. However there is some cross reactivity among tree nut families so caution is warranted. We have some information on this through research that involves testing blood serum from tree nut allergic people against all tree nut proteins that are known. Other research involves giving tree nut allergic people oral food challenges with different nuts and observing them for reactions.
For more on this go to (http://foodallergies.about.com/od/nutallergies/p/treenutallergy.htm).
If you want to see some of the science of cross reactivity studies using double immunodiffusion go to http://treenuts.ca/nutallergy.pdf.
“Am I just nuts to do this?”
Seeing the allergy specialist was the right move for her. The new Food Allergy Guidelines certainly advises people with these types of questions to see a specialist for a discussion of testing options. My wife’s friend made an appointment to see me and I skin tested her to all the nuts. She had positives to cashew and pistachio which are known to be cross reactive. She was negative to another family of tree nuts (walnut and pecan). She underwent a food challenge in the office to both and did well. She decided to go ahead and eat these as she was reassured that the risk of reaction was very low. At last report she enjoyed both walnuts and pecans this Christmas season and was thrilled. She continues to avoid cashews, will not eat pistachios, and keeps her epinephrine injector in her purse just in case.