Resolution of Peanut Allergy
ABSTRACT & COMMENTARY
Synopsis: Children with a history of allergic reactions to peanuts may either lose reactivity (resolvers) or remain allergic (persisters), as determined by reactions to a challenge with peanuts. Some of the resolvers had positive skin pricks to peanut. A challenge is the only way to identify children who are no longer at risk.
Source: Hourihane J O'B, et al. Resolution of peanut allergy: Case control study. BMJ 1998;316:1271-1275.
Thirty children with a history of significant allergic reactions to peanuts were studied by reactions on rechallenge with peanut, skin test prick with peanut, and serum total and peanut specific IgE levels. Fifteen children did not have allergic reactions to peanut challenge and were designated as "resolvers."The remaining 15 children had allergic reactions on rechallenge with peanut and were designated as "persisters." On skin prick testing with peanut, all children, both resolvers and persisters, had positive responses, but only three of 14 had a weal of more than 6 mm. Total serum IgE and peanut specific IgE levels did not differ between the two groups. Allergy to other foods was reported more frequently in persisters than responders. Many children (as many as 50%) with a history of allergic reaction to peanut will be tolerant when rechallenged, despite a positive skin prick test with peanut. Appropriately trained clinicians should be prepared to perform appropriate challenge preschool children, with a history of peanut allergy, taking appropriate precautions in case they are still intolerant.
COMMENT BY FRANK GRUSKAY, MD, FAAP
Peanuts are probably the most common cause of death by anaphylaxis to foods in the United States. About 30% of peanut allergic individuals have severe reactions. Peanuts are added to a large variety of processed and restaurant foods including Chinese food, candy, breakfast cereal, frosting, ice cream, snack foods, and bakery products. Insufficient labeling can obscure the presence of peanuts in these foods. Many case reports suggest that minute quantities of ingested peanuts are sufficient to trigger allergic reactions including fatal or near fatal anaphylaxis.
Hourihane and associates from the South Manchester University Hospital report on a small group of patients with a history of reaction to peanut ingestion. Fifteen of 30 children had no reaction to an open oral challenge to peanut. These investigators suggest that the size of the weal on skin testing may predict which child will react to oral challenge.
Studies by Bock and associates have shown that prick skin tests have a negative predictive value approaching 100% when compared to the "gold standard," a double-blind placebo controlled food challenge, and a positive predictive value of 50-60%.1 This figure is even higher in children younger than 2 years of age. The same study demonstrated that the size of the skin test reaction is not correlated with a positive food challenge. Sampson and associates reported that a CAO-RAST IgE result of 15 units/mL or more correlated with a 92% chance that the patient will react to challenge with the particular food.2 In a study at the National Jewish Center, none of the 32 patients with peanut allergy followed for 16 years lost their clinical sensitivity. Sampson found that 80-90% of children with atopic dermatitis lost their clinical sensitivity to milk or egg with long-term follow-up, but none lost it to peanuts.3
It seems risky in light of these studies for clinicians to consider a rechallenge of peanut allergic children as defined by positive history and demonstrated IgE antibody to peanuts. Such a challenge may result in a potentially life-threatening reaction. (Dr. Gruskay is Associate Clinical Professor and Head of the Allergy Clinic at The Children's Hospital at Yale New Haven.)