Clinical study of peanut and nut allergy in 62 consecutive patients: new features and associations.

By Pamela W. Ewan

There has been an apparent increase in cases of allergies in recent years, with nut allergiesappearing especially important both in the number of cases and in the severity of reactions. In1993, six patients in the United Kingdom died of peanut allergy. But despite the media attentionthese occurrences generate, there have been few studies to help elucidate how such allergiesdevelop and decide on appropriate management of allergic patients.

This study reports on 62 patients with nut allergies in one doctor's practice who were seen fortheir allergies in 1993 and 1994. They were predominantly children, but all age groups wererepresented: 23 patients between 11 months and five years, 29 between five and 18, eight between19 and 32, and two patients older than 32. Each patient provided a detailed history of previousallergic reactions and other allergy-associated disorders such as asthma, rhinitis and eczema. Theirrespiratory function was assessed and medications were noted. To further investigate coexistentallergies, skin prick tests were performed, using a number of other nut and legume extracts as wellas a routine screen of 13 common allergens such as cat dander and dust mites.

Several of the patients had allergies to more than one type of nut. Peanuts, which are not in factnuts but edible seeds of a species of lentil, were the most common cause of allergy, appearing in47 of the 62 patients. They were followed by Brazil nut (18 patients), almond (14), hazelnut (13),and walnut (eight); only three patients displayed allergy to cashew nut. Of the 25 patients withmultiple nut allergies, peanuts were involved in 19.

Sensitization to nuts occurred early in life, with 11 patients being sensitized in their first year oflife and 33 before age three. Fully 92% were sensitized at some point before age seven, andpeanuts were the main cause of sensitization in most of these cases. Almost invariably, very youngchildren displayed a single allergy to peanuts, with some going on to develop allergies to othernuts later in childhood. By age seven, 15 of the 41 children with peanut allergy were also allergicto other nuts. This pattern suggests that there has been a real increase in the prevalence of nutallergy through early sensitization, and not just an increase in reporting.

The severity of allergic reactions ranged from skin irritation, to respiratory symptoms such asswelling of the throat and asthma, to loss of consciousness. Facial swelling was common,occurring in 52 of the patients, and respiratory symptoms ranged from very mild to asphyxia. Themost severe reactions (choking, throat obstruction, respiratory difficulty) were seen in adultpatients, all of whom developed symptoms within minutes of ingesting the allergen, and all ofwhom had multiple allergies, with nut allergies being present since early childhood. Two of theadult patients went into respiratory arrest, lost consciousness and had to be intubated (havebreathing tubes inserted into the lungs).

Skin prick tests were used to diagnose the nut allergy and identify other allergies by detectingspecific IgE antibodies to particular substances. The tests confirmed the nut allergy diagnosis in allbut one of the 62 patients, and found sensitivities to other common allergens in almost all of them.Those who tested positive had symptoms such as asthma or rhinitis triggered by these otherallergens. Interestingly, only four patients were allergic to pulses (edible seeds of peas, beans andlentils) other than peanuts, while almost a third of the group also had allergies to tree nuts.

Patients with peanut allergy, especially if it develops early in childhood, should be considered atrisk of developing allergies to tree nuts. Early sensitization is common, with many of the childrenfirst reacting to peanut butter given to them before age one. There is also a suggestion in thisstudy that people who develop peanut and nut allergies are highly allergy-prone, with manydeveloping reactions to common inhaled allergens as well.

Children of previous generations had much simpler diets, with peanuts and nuts not usuallyintroduced until later in life, and there seems to be a case for avoiding them during the periodwhen sensitization is common, possibly up to seven years of age. For those with acute reactionsto peanuts and nuts, avoidance is essential, and inadvertent ingestion through improper labelingand low awareness among food manufacturers remains a significant risk.

Questions for Dr. Ewan:

1. Could eliminating exposure to peanuts and nuts in childhood prevent the development ofallergies?

That's difficult to answer. We need much more data over a long period of time to be certain. Oneof our hypotheses is that the early introduction of peanuts is an important factor responsible forthe increase in peanut allergy. If that's right, delaying introduction might lead to prevention of thisallergy. It's known for certain in other allergies that small children, if exposed to a potent allergen,seem to be more likely to react. We have not seen this large number of young children withpeanut allergy until recently, so something has changed, and one of a number of things that havechanged is diet.

2. Have you seen cases of adults who have been eating peanuts all their lives, and suddenlyget a reaction?

Very few. We do see that, but it's uncommon, although allergies can develop at any age.

3. Can skin tests be dangerous to young children?

Skin tests are very safe, but it's important that they be done in expert hands, because occasionallyyou get a reaction. We tested large numbers of nut-allergic people, including very young ones,and we saw no adverse reactions.

4. Do genetic factors predispose to nut allergy or other allergies?

That's certainly true of other allergies, and I presume that it will apply to nut allergy as well. Ithas been known for a very long time that if one parent is allergic, there's a good chance the childwill be, and if both parents are, the chance is even greater. But it's not a direct inheritance. It'svery complex trying to disentangle the link between genes and the development of allergicantibody responses. In this study, almost all of the patients who were nut-allergic also had othercommon allergies, so they were clearly of a background genetically predisposed to allergy.

5. Can an infant be sensitized through breast milk?

Probably. We know that proteins from the maternal diet can get into breast milk. This has beenestablished with other foods, so there's no reason it couldn't happen with peanuts, although as faras I know this hasn't been properly demonstrated. You must have been previously exposed inorder to produce the antibody which causes the allergic reaction, so theoretically it couldn't occuron your first exposure. Cases where the mother is sure that a reaction occurred the very first timethe baby was given peanut in any form raise issues like "Could it have been from breast milk?".It's postulated that tiny amounts of the protein in the mother's milk might be enough to sensitizethe baby -- in other words, cause him to manufacture the harmful allergic antibody to the protein.Another possible way could be across the placenta, in utero. If the mother is eating a lot ofpeanuts during pregnancy, it's theoretically possible for the proteins to cross the placental barrierinto the baby.

6. To what factors do you attribute the increase in allergies?

In the last 10 to 20 years, there has been a huge increase in the number of allergic disorders.Earlier or more frequent exposure to allergens is one important factor, but I don't think it's theonly one. Another is atopy, the tendency to form allergic antibodies. An atopic child exposed topeanut butter is at much greater risk of developing peanut allergy than a normal child. We foundatopy in 96% of the patients in the study by carrying out skin prick tests to other commonallergens. The same number had other common allergic disease -- allergic asthma or rhinitis, oratopic eczema. One theory is that it's in part to do with modern living. The way we live now, inenclosed environments with central heating, carpets and double-glazed windows, favours thegrowth of the house dust mite, which is one of the commonest causes of asthma, rhinitis andeczema. That may be a very important factor, and there may be others that we don't yet have dataon.

Comment from Dr. Ewan:

One thing our study suggests is that if you have a child with a common allergy, it's very unwise togive that child peanuts or nuts. It may well be that the same advice is valid even for children whoaren't allergic, but we don't yet have data to support that. But if you have an allergic child, thereare very strong reasons for at least delaying the introduction of peanuts and nuts, and certainly tonot give them to very young children. It's a fearsome allergy -- it's a very dangerous thing tohave. It can have such terrible consequences, so if there's any way of avoiding it, that would besensible to do.

Clinical study of peanut and nut allergy in 62 consecutive patients: new features andassociations.

Pamela W. Ewan.

Objective: To investigate clinical features of acute allergic reactions to peanuts and other nuts.

Design: Analysis of data from consecutive patients seen by one doctor over one year in an allergyclinic at a regional referral centre.

Subjects: 62 patients aged 11 months to 53 years seen between October 1993 and September1994.

Main outcome measures: Type and severity of allergic reactions, age at onset of symptoms, typeof nut causing allergy, results of skin prick tests, and incidence of other allergic diseases andassociated allergies.

Results: Peanuts were the commonest cause of allergy (47) followed by Brazil nut (18), almond(14), and hazelnut (13). Onset of allergic symptoms occurred by the age of two years in 33/60 andby the age of seven in 55/60. Peanuts accounted for all allergies in children sensitized in the firstyear of life and for 82% (27/33) of allergies in children sensitized by the third year of life. Multipleallergies appeared progressively with age. The commonest symptom was facial angioedema, andthe major feature accounting for life threatening reactions was laryngeal oedema. Hypotensionwas uncommon. Of 55 patients, 53 were atopic -- that is, had positive skin results of tests tocommon inhaled allergens -- and all 53 had other allergic disorders (asthma, rhinitis, eczema) dueto several inhaled allergens and other foods.

Conclusions: Sensitization, mainly to peanuts, is occurring in very young children, and multiplepeanut/nut allergies appear progressively. Peanut and nut allergy is becoming common and cancause life threatening reactions. The main danger is laryngeal oedema. Young atopic childrenshould avoid peanuts and nuts to prevent the development of this allergy.

British Journal of Medicine 1996; 312:1074-8.