Food allergy and eosinophilic esophagitis: Learning what to avoid
ABSTRACTFood allergies have increased in prevalence significantly in the past decade and so, apparently, has eosinophilic esophagitis. Although the cause of eosinophilic esophagitis is unknown, allergic responses including food allergies have been implicated. This article reviews both conditions, focusing on how to detect and manage them.
KEY POINTS
- Food allergies can be classified as mediated by immunoglobulin E (IgE-mediated), non-IgE-mediated, or mixed. Their clinical presentation can vary from life-threatening anaphylaxis in IgE-mediated reactions to chronic, delayed symptoms as seen in eosinophilic esophagitis (a mixed reaction).
- The diagnosis of an IgE-mediated food allergy is made by taking a complete history and performing directed testing—skin-prick testing or measurement of foodspecific IgE levels in the serum, or both.
- Despite promising developments, food allergies continue to be treated primarily by telling patients to avoid allergens and to initiate therapy if ingestion occurs.
- Because most patients with eosinophilic esophagitis have a strong history of atopic disease and respond to allergen-free diets, a complete evaluation by a specialist in allergy and immunology is recommended.
Three types of immune responses to food
Immunologic reactions to foods can be divided into three categories: mediated by immunoglobulin E (IgE), non-IgE-mediated, and mixed. Therefore, these disorders can present as an acute, potentially life-threatening reaction or as a chronic disease such as eosinophilic gastoenteropathy.
IgE-mediated reactions are immediate hypersensitivity responses. In most patients, an IgE-mediated mechanism can be confirmed by a positive skin test or a test for food-specific IgE in the serum. In this article, the term “food allergy” refers to an IgE-mediated reaction to a food, unless otherwise indicated.
Non-IgE-mediated reactions have a delayed onset and chronic symptoms. Commonly, they are confined to the gastrointestinal tract; examples are food-protein-induced enterocolitis, proctitis, and proctocolitis and celiac disease.3,26,27 However, other diseases such as contact dermatitis, dermatitis herpetiformis, and food-induced pulmonary hemosiderosis (Heiner syndrome) are also considered non-IgE-mediated allergies.
Mixed-reaction disorders are chronic and include the eosinophilic gastroenteropathies, ie, eosinophilic proctocolitis, eosinophilic gastroenteritis, and eosinophilic esophagitis.28 The pathophysiology of these diseases is poorly understood. Many patients have evidence of allergic sensitivities to food or to environmental allergens, or both, but whether these sensitivities have a causal role in these disorders is not clear.
Atopic dermatitis, another complicated disease process, may be associated with mixedreaction food allergy, as approximately 35% of young children with moderate to severe atopic dermatitis have food allergies.29
Diagnosis of IgE-mediated food allergies
A thorough history and physical examination are key to diagnosing an IgE-mediated food allergy.
The history should include potential culprit foods, the quantity eaten, the timing of the onset of symptoms, and related factors such as exercise, alcohol intake, or medication use. Symptoms of an IgE-mediated reaction are generally rapid in onset but may be delayed up to a few hours, while non-IgE mediated symptoms may present several hours to days later.
Food challenge. A double-blind, placebocontrolled oral food challenge is the gold standard for the diagnosis of food allergies. (The food to be tested is hidden in other food or in capsules.) However, this test poses significant risks, and other diagnostic methods are more practical for screening.
Skin-prick tests with commercially available extracts are a rapid and sensitive method of screening for allergy to several foods.
Negative skin-prick tests have an estimated negative predictive value of more than 95% and can therefore exclude IgE-mediated food allergies.
A positive test indicates the presence of IgE against a specific food allergen and suggests a clinical food allergy, although the specificity of the test is only about 50%, making a positive result difficult to interpret. Although the size of the skin-test response does not necessarily correlate with the potential severity of a reaction, a response larger than 3 mm does indicate a greater likelihood of clinical reactivity. A positive test is most helpful in confirming the diagnosis of IgE-mediated food allergy when combined with a clear history of food-induced symptoms.
The proteins in commercially based extracts of most fruits and vegetables are often labile; therefore, skin testing with fresh fruits and vegetables may be indicated.30
Immunoassays. Radioallergosorbent tests (RASTs) and fluorescent enzyme immunoassays are used to identity food-specific IgE antibodies in the serum. The commercially available tests do not use radioactivity, but the term “RAST” is still commonly used.
Immunoassays are generally less sensitive and more costly than skin-prick tests, and their results are not immediately available, unlike those of skin-prick testing. However, these in vitro tests are not affected by antihistamine use and are useful in patients with severe dermatologic conditions or severe anaphylaxis, for whom skin-prick testing would not be appropriate.
However, unlike a negative skin-prick test, an undetectable serum food-specific IgE level has a low negative predictive value, and an undetectable level may be associated with symptoms of an allergic reaction for 10% to 25% of patients.29 Therefore, if one suspects an allergic reaction but no food-specific IgE can be detected in the serum, confirming the absence of a clinical allergy must be done with a skin-prick test or with a physician-supervised oral challenge, or both.
Managing food allergy by avoiding the allergen
Food allergies are managed by strictly avoiding food allergens and by taking medications such as self-injectable epinephrine for anaphylactic symptoms.
Patients and caregivers must be educated about reading food labels, avoiding high-risk situations such as eating at buffets and other restaurants with high risk of cross-contamination, wearing a medical-alert bracelet, recognizing and managing early symptoms of an allergic reaction, and calling for emergency services if they are having an allergic reaction. Since January 2006, the US Food and Drug Administration has required food manufacturers to list common food allergens on food labels (cow’s milk, soy, wheat, egg, peanut, tree nuts, fish, and shellfish), and the labeling must use simple, easily understood terms, such as “milk” instead of “whey.” However, it is still prudent to read all ingredients listed on the label.
