August 2002, VOLUME110 /ISSUE Supplement 2

The Natural History of Peanut Allergy

  1. James R. Banks, MD,
  2. Arnold, MD

Purpose of the Study. It has traditionally been thought that peanut allergy, once established, almost always lasts lifelong. These investigators sought to determine the frequency with which peanut allergy is actually outgrown and identify any characteristics in these children that might predict this tendency.

Study Population. A total of 223 patients with a diagnosis of peanut allergy were identified by chart review in two tertiary care allergy clinics and one private practice. Patients were determined to be peanut allergic if they had a positive history and positive results to a skin test, radioallergosorbent test (RAST) or challenge; or in some cases positive tests in the absence of any known exposure.

Methods. A questionnaire was administered to all study patients that detailed the nature of the reaction, age of onset, any other food sensitivities and their resolution or lack thereof, and history of other atopic diseases. Most patients were skin tested for peanut, and CAP RASTs were obtained. Patients with histories of strictly cutaneous symptoms after peanut ingestion and RASTs <20 kU/L were asked to participate in peanut challenges. Those with histories of more severe reactions were asked to participate in challenges only if RASTs were <10 kU/L. Both double-blind, placebo-controlled and open food challenges were used. All negative challenges were confirmed by open challenge.

Results. Seventy-five percent of the patients had a history of acute reaction to peanut, while 5% had positive peanut skin tests or RASTs and a history of marked improvement in atopic dermatitis with a peanut-restricted diet. Approximately 25% had positive test(s) but were not known to have ever ingested peanut. Of the 223 patients (ages 4–20 years) evaluated, 126 were eligible for challenges, and 85 subsequently underwent such challenges. Forty-eight (21.5%) had negative results, and 37 reacted. Peanut RASTs of those who underwent challenges were different for those who passed (median 0.69 kU/L) versus those who failed (median 2.06 kU/L) at time of challenge but not a time of diagnosis. Patients who had negative challenges were significantly more likely to have had an initial reaction with involvement of the skin alone than those with ongoing peanut allergy. Yet, 17% of those with cutaneous only reactions had RASTs >20 kU/L and therefore were ineligible for challenge. One child with a reaction involving cutaneous, respiratory, and gastrointestinal systems outgrew his allergy. Six patients with negative RASTs had positive challenges that ranged from simple cutaneous to multisystem involvement.

Conclusions. Peanut allergy is outgrown in approximately 22% of children, especially in those with histories of cutaneous only reactions and with currently low peanut RASTs. Although children with initial RASTs >10 kU/L are unlikely to lose their sensitivity, younger patients should have RASTs monitored annually until at least age 4 years. Challenges in controlled settings should be offered to appropriate patients, because the benefit provided to those who are no longer allergic clearly outweighs the risk of a carefully performed challenge.

Reviewer’s Comments. This reviewer recently peanut challenged a 4-year-old asthmatic girl with a history of persistent cow milk allergy, distant history of positive peanut puncture skin test, no known lifetime exposure to peanut, and currently negative peanut RAST, with resultant biphasic anaphylaxis. Earlier studies have shown that asthma is a major risk factor for life-threatening allergic reactions to peanut, yet any asthmatic children lost their peanut sensitivity in this study. These various observations do not suggest less aggressive avoidance measures or less diligence with adrenaline contingency plans; but closer monitoring of peanut immunoglobulin E with an eye toward ultimate challenge in qualifying children. Does avoidance of peanut at a critical time in life in sensitized children truly alter the natural history of this allergy in some? Also, it would be interesting to know if the natural history of peanut allergy is different in that smaller group of persons who begin with such sensitivity in adulthood.