AAD: Untangling the Web of Eczema and Food Allergies
EXPERT ANALYSIS FROM THE AMERICAN ACADEMY OF DERMATOLOGY'S SUMMER ACADEMY MEETING
NEW YORK – Children with atopic dermatitis have a high risk of food allergies – although these allergies are not always easy to pinpoint.
"In this population, up to 20% of [those] with mild to moderate atopic dermatitis and 30%-40% of the severe patients will have a true food allergy," that can be confirmed with an open food challenge. Dr. Lawrence F. Eichenfield said at the American Academy of Dermatology’s 2010 meeting.
However, he said, positive skin prick testing – a common form of allergen identification – isn’t a very accurate way to detect the allergies. As a result, parents of children with atopic dermatitis (AD) will frequently state that their child has a food allergy, when, in fact, none exists.
A new national guideline helps clarify that issue, he said. Published in late 2010, "Guidelines for the Diagnosis and Management of Food Allergy in the United States," from the National Institute of Allergy and Infectious Diseases, provides some helpful information for dermatologists trying to make the AD/food allergy connection.
The document defines a food allergy as an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food. Skin prick testing, however, can only identify sensitization to a food, which doesn’t necessarily correlate with a clinical event, said Dr. Eichenfield, a professor of clinical pediatrics and dermatology at the University of California, San Diego.
"It’s very clearly written in the guidelines that an individual can develop allergic sensitization without having clinical symptoms on exposure to the food. Therefore, skin testing is not sufficient to say there is a food allergy."
Nevertheless, a common clinical scenario in the pediatric dermatology office is a parent who claims the child is allergic to a given food – most often eggs, soy, milk, wheat, or peanuts – because of a positive skin test. "What people don’t understand is, these tests are neither very sensitive nor specific," he said.
The specificity of skin prick testing hovers at about 85%, while the sensitivity is around 75%. "That means if we assume a 5% true milk allergy in a group of 1,000 people, skin prick testing will identify 42 of the 50 with a true allergy, miss 8 of those with the allergy, and give a false positive result to 238 people without the allergy," he said. "It’s a problem when you start labeling someone as having an allergy with just a positive test, but no clinical indicator."