From Medscape Allergy & Immunology
Highlights of the NIAID Guidelines
Laura A. Stokowski,
Posted: 03/17/2011
Dermatology and Food Allergy
Food allergy is an immune-based disease that may be increasing in prevalence in the United States. Fears about food allergy have become heightened in the general public, although many of these fears are born of myths and misunderstandings about food allergy that occasionally are perpetuated by healthcare professionals.
The National Institute of Allergy and Infectious Diseases (NIAID) recently issued Guidelines for the Diagnosis and Management of Food Allergy in the United States ,which are a "harmonization of best clinical practices related to food allergy across a wide range of medical specialties." The guidelines address misconceptions surrounding food allergy and attempt to improve the diagnosis and management of this widespread condition. For more information about the NIAID guidelines, see Food Allergy: The Definitive Guide to Clinical Practice .
Patients with suspected food allergy present to many different settings for care depending on the nature and severity of their symptoms. One such setting is the dermatology practice, where the typical nonurgent presentation of a patient with potential food allergy is the infant or child with atopic dermatitis (AD).
A skin-based treatment regimen is recommended for most patients with AD, but parents often wonder whether their child's AD suggests an underlying food allergy that warrants either further testing or dietary restriction.
Atopic Dermatitis
AD (also known as atopic eczema) is a red, scaly, pruritic chronic inflammatory rash that is 2-3 times more prevalent than it was 40 years ago.
This remitting and relapsing disorder also shows predilection for certain body sites: the face, scalp, neck, and extensor surfaces in infants; and the flexural areas (such as the back of the knees and front of elbows) and the hands in children and adults. The skin of affected individuals is often very dry.
AD is managed primarily with topical corticosteroids, emollient therapy, and education about skin care for affected children.
Many children outgrow AD by the time they reach adolescence.
In the meantime, however, AD can have a significant impact on the child's quality of life. It is not surprising that parents seek an explanation for their child's AD, hoping that perhaps a quick fix will be offered by food allergen avoidance, or fearing a life-threatening reaction that could be prevented by taking simple precautions.
The Real Connection Between Atopic Dermatitis and Food Allergy
Children with AD, those with a family history of atopy, and those with concurrent asthma or hayfever are at risk for the development of food allergy.[1] However, this risk is lower than many people believe, and the true nature of the link between AD and food allergy has long been a source of misinformation.
"Many think the disease [AD] is caused by the food allergy, whereas it's the other way around. Food allergy is caused by the disease," explains Jon Hanifin, MD, a specialist in AD from Oregon Health Sciences University Department of Dermatology, and coauthor of the NIAID food allergy guidelines. In most patients with coexisting AD and food allergy, AD precedes the food allergy.
Dr. Hanifin emphasizes that the likelihood of an infant or child with AD having food allergy must be kept in perspective. Dr. Hanifin and colleagues recently completed a 5-year multicenter study in infants age 3-18 months and found that even in reported mild cases of AD, roughly 15% of infants had definite food allergies.
The more severe the AD, the higher the risk for food allergy. In patients with moderate-to-severe AD, the prevalence of food allergy may be as high as 30%-40%. "We must remember, however, that 85% of infants with AD don't have food allergy," says Dr. Hanifin.
Patients with AD typically have higher levels of immunoglobulin E (IgE) antibodies; in the past this has been interpreted as evidence of food allergy causation. Dr. Hanifin emphasizes that elevated IgE antibodies are evidence only for sensitization to a food but are not proof of a food allergy.
The presence of antibodies is a consequence of the pruritic nature of AD, causing children to scratch their skin, allowing food allergens to be absorbed via this disrupted skin barrier, and inducing the development of antibodies.
"AD usually comes on in infancy, before any possible food reactions, and the cellular infiltrate in the skin of patients with AD does not reflect a specific allergic reaction. The major stimulus for the cellular reaction seems to be irritants," explains Dr. Hanifin. "The only proven allergic response is IgE-mediated, and the relative frequency of those reactions seems tied to absorption and sensitization to food proteins through the defective barrier."
Furthermore, emphasizes Dr. Hanifin, "An immediate reaction to food -- usually within 30 minutes -- hives, lip swelling, vomiting, is required for diagnosis of food allergy."
The knowledge that AD is a precursor to rather than a consequence of food allergy has not eradicated all of the uncertainty about which children ought to be formally tested for food allergy. It is still not uncommon to see such testing initiated solely on the basis of a bout of AD. The NIAID guidelines attempt to provide unambiguous recommendations for testing children with AD for food allergy.
Which Patients With Atopic Dermatitis Should Be Tested for Food Allergy?
The link between AD and food allergies compels practitioners to conduct or refer patients for appropriate testing for food allergy, but only when specific criteria are met. With the high prevalence of AD in children (as high as 17% in school-aged children, testing every child for food allergy is neither practical nor useful.
Insufficient evidence supports a specific age for testing response to foods known to cause IgE-mediated food allergy in infants or young children with AD.
In weighing benefit vs harm, the NIAID guidelines recommend 2 indications for consideration of food allergy testing (milk, egg, peanut, wheat, and soy) in children younger than 5 years with moderate-to-severe AD:
1. A child who has persistent AD despite optimized management; or
2. A child who has a reliable history of an immediate reaction after eating a specific food.
In these children, the benefits of diagnosing food allergy at an earlier age include better management of food allergy and prevention of a severe reaction to an allergen. However, it is also recognized that such testing is time-consuming and expensive and could lead to overly restrictive diets in these children.
Care should be taken to ensure that a child is clinically allergic to a food prior to removing it completely from the child's diet.
Appropriate testing for a clinical food allergy means an oral food challenge, conducted by experienced specialists in a controlled medical setting that has appropriate supervision, medications, and equipment for managing anaphylaxis.
Food allergy testing is also indicated in individuals who present with anaphylaxis or symptoms (cutaneous, respiratory, gastrointestinal, and/or cardiovascular) that occur within minutes to hours of ingesting food, and/or if the symptoms have occurred following ingestion of a specific food on more than a single occasion.
Managing Food Allergy Concerns in Patients With Atopic Dermatitis
In practice, the clinician is often faced with parents' overriding concern about food allergy in the infant or child with AD.
Dr. Hanifin describes a typical scenario. "A baby with inflamed cheeks (irritation of AD from feeding) is brought in to the office. The parents think their child is having a food allergy reaction. The physician agrees, or is not certain, and tells the parents to stop giving milk, and sends them to an allergist who does blood or skin tests. Of course, the infant has high levels of antibodies, and the parents are told to restrict 1 or more foods which can, in some cases, lead to malnutrition and nutrient deficiencies. Ironically, these antibodies are not necessarily diagnostic for food allergy."
What should happen when parents bring in a child with AD starts with a careful history. If no history of an immediate reaction to food is revealed, the parents should be advised that although their child is at risk for food allergy, AD alone is not evidence of food allergy. They should be educated about true food allergy and the immediate nature of food allergy symptoms. "Otherwise," adds Dr. Hanifin, "they will chase every flare of AD as if it is an allergic reaction to food. AD can flare for any number of reasons: stress, infection, or even cold, dry weather."
Another misconception is that food allergy exacerbates AD, lending support to the role of food exclusion in the management of AD. Current evidence suggests that for the most part, food exclusion does not improve or prevent AD. However, the NIAID guidelines point out that some research has documented improvements in pruritus when patients with egg allergy avoided egg consumption.The bottom line is that in individuals without documented or proven food allergy, avoiding potentially allergenic foods as a means of managing AD is not recommended. Unwarranted food avoidance, particularly in children, can produce nutritional deficiencies and adversely affect growth.
Summary
Food allergy and AD are clearly related conditions, but this relationship is frequently misunderstood and often assumed to be more prevalent than it really is. To avoid unnecessary pain, expense, anxiety, and nutritional deficiency, clinicians should generally stick to the NIAID guidelines and refer for appropriate food allergy testing only those patients who have evidence of IgE-mediated immediate reaction to a food or who meet additional criteria detailed in the guidelines. Management of the active clinical condition -- the AD -- and education of the parents about the risk for and symptoms of true food allergy are the mainstays of care for these patients.
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