Reviewer: S. Randhawa, M.D., Allergist/Immunologist and Assistant Professor at NSU
A 9-year-old boy is referred by his pediatrician for evaluation of suspected food allergy to tree nuts - walnuts, hazelnuts and pistachios. He complains of oral itching, hypersalivation and hives immediately after eating any of the tree nuts listed above. Symptoms started at the age of 4 year and he started to avoid tree nuts. He occasionally has recurrence of symptoms when accidentally eating foods containing tree nuts without checking the label. He had one episode of wheezing after eating walnuts that required a brief ER visit. His mother has brought the ImmunoCAP test results ordered by his pediatrician.
Past medical history (PMH)
Family medical history (FMH)
ImmunoCAP (specific IgE)
What is the most likely diagnosis?
The patient's symptoms are typical of food allergy syndrome. An estimated 1-2% of the population in the USA is allergic to peanut and/or tree nuts.
Can he eat other tree nuts?
The patient was advised against eating other tree nuts such as almonds and Brazil nuts due to risk of potential cross reactivity. Cashews and walnuts are the most common tree-nut allergens, followed by pecans.
Peanuts are not tree nuts but legumes (peas, beans, lentils, soy; the term "legumes" is believed to come from the Latin verb legere "to gather") and the patient reports no symptoms when consuming peanuts. He also was advised against picking just the peanuts from a container with mixed nuts -- the nuts antigens are proteins and are often found in the powder surrounding the packaged nuts.
There is a 40% potential for cross-reactivity between peanuts and almonds/cashews.
There is a difference between cross-reactivity and cross-contamination. Cross-contamination occurs when a food that does not itself contain any allergens is tainted with an allergen during food preparation, cooking, storage, or serving. For example, a mother thinks her son is allergic to raisins because he develops symptoms when eating only raisins from a trail mix. In fact, he is allergic to the peanuts in the mix which cross-contaminate the raisins.
What is the chance that he will "outgrow" the tree nut allergy?
Around 9%. The relative resolution of the tree nut allergy can be verified by monitoring the specific IgE level every year. One in 5 children outgrows allergies to peanuts but peanuts are legumes, not tree nuts. In other words, only 20% of those with peanut allergy, and 9% of those with tree nut allergy, are reported to acquire tolerance. Additionally, peanut allergy can recur, with one study finding a recurrence rate of 8%.
What would you recommend to the patient?
1. Avoid all tree nuts.
2. Check the labels. If the food was manufactured in a facility which processes tree nuts, do not eat it.
3. Suck on suspicious food before swallowing it (such as in restaurants despite getting clearance from the cook). If the allergy symptoms recur, spit it out.
4. Carry 2 EpiPen Jr. at all times.
5. A letter for the school is given by the allergist.
6. Specific IgE to almonds and hazelnuts should be checked annually.
Peanut and tree nuts are the foods most frequently associated with fatal episodes of anaphylaxis.
How long does it take for the allergy medications to work?
EpiPen works within minutes, the effect feels almost immediate.
Benadryl works withing 45 minutes, therefore the effect is not immediate.
Can you do skin prick testing for food allergies?
Yes. 13% of children who have negative skin tests to, for example, peanut, will have positive oral challenges to this food (AAAAI Ask the Expert, 2012).
When is it safe to perform a food a challenge for food allergies?
The relative safety of a food challenge is determined by the levels of specific IgE. Undetectable level on ImmunoCAP is not the same as "zero" risk. May allergists think that skin prick testing is more clinically relevant than ImmunoCAP. In theory, intradermal skin testing is more sensitive than skin prick testing and as close to "absolute zero" in terms of reactivity as one can reasonably get. In practice, however, intradermal skin testing is not done with food allergens.
Relative sensitivity of ImmunoCAP, skin prick testing and intradermal testing. Image source: Adapted from Dr. Hopp, Creighton University Division of Allergy & Immunology, used with permission.
There are predetermined levels of specific IgE on ImmunoCAP below which a food challenge can be attempted. Those levels are shown in the grid below:
Levels of specific IgE below which a food challenge can be attempted. Image source: Dr. Hopp, Creighton University Division of Allergy & Immunology, used with permission.
The specific IgE levels were determined for milk, egg white, peanut, wheat and soy. Currently, no such recommendations exist for tree nuts and fish.
When to use EpiPen?
When there is a progression of symptoms or at any time when the symptoms make parents or the child worried. One should be careful not to inject the thumb when using the EpiPen.
What to do after the EpiPen is used?
If symptoms are better, the patient should go to the ER for further evaluation. If the symptoms are not better, the parents should call 911 and consider using the second dose of EpiPen. An EpiPen is only good for a year and two of them should be available at all times (a twin pack). Used EpiPen are safely disposed off by the ER personnel.
Tree nut allergy.
Mind map of food allergy.
Diagnostic algorithm for food allergy: SAD Child:
1. Symptoms: close relation between specific food intake and symptoms, often affect 2 or more organs
2. Allergy testing: skin prick testing or ImmunoCAP.
3. Diagnostic diet: restricted diet leads to symptoms disappearance or significant reduction.
4. Challenge - oral food challenge.
References: Clinical review: ABC of allergies, Food allergy. BMJ 1998;316:1299, figure.
The 8 top allergens, which account for 90 % of all food allergies, can be remembered by the following mnemonic: TEMPS WFS
Tree nuts (almonds, cashews, walnuts)
Egg white (not egg yolk)
Shellfish (crab, lobster, shrimp)
Fish (bass, cod, flounder)
Oral Food Challenges (click to enlarge the diagram).
8 top allergens account for 90 percent of food allergies. Specific IgE levels (sIgE) that predict the likelihood of passing an oral food challenge are shown in the figure. (click to enlarge the image).
What is the most common food allergy in children?
Cow's milk allergy is the most common childhood food allergy.
Manifestations of food allergy: GRAS
GI - N/V/D/pain
Respiratory - less common, usually in association with either skin/GI symptoms and seldom as an isolated manifestation
Anaphylaxis - most dangerous
Skin - most common
Peanut and tree nut allergy in childhood. Pediatr Allergy Immunol. 2008 Jun;19(4):368-73.
Nut Allergies May Be Outgrown. Medscape, 2005.
Image source: Wikipedia, GNU Free Documentation License.
Living With a Nut Allergy. WebMD.
Tree Nut Allergy Diet. NewYork-Presbyterian Hospital.
Food Allergen Avoidance. V. Dimov, Oct 2008.
Cross Reactions Among Foods (PDF).
"Allergic to cashews, but thought it would be OK to eat almonds on AirFrance flight" - allergist on board saved his life http://goo.gl/P8Yh4