KEYSTONE, COLO. Young children who have atopic dermatitis without recurrent wheezing do not face an increased risk of developing asthma by school age.
This is a question that often is asked by worried parents who have read about the atopic march, the theory that early atopic dermatitis predisposes to a disease progression including food allergies, allergic rhinitis, and ultimately asthma, Dr. Joseph D. Spahn said at a meeting on allergy and respiratory disease. Reassurance that this is not the case in children with atopic dermatitis without respiratory symptoms comes from the landmark Multicentre Allergy Study (MAS), said Dr. Spahn of the medical center and the University of Colorado at Denver.
The MAS study, funded by the German Federal Ministry of Education and Research, prospectively followed 1,314 children in five cities from birth to age 13 years. Allergic sensitization to house dust mites, cat and dog hair, and other perennial allergens was assessed six times from ages 110 years. Lung function was measured at 7, 10, and 13 years. Environmental exposure to allergens was evaluated via home visits at ages 6 and 18 months and at 3, 4, and 5 years.
In MAS, the cumulative prevalence of atopic dermatitis in the first 2 years of life was 21.5%. The great majority of affected children outgrew their atopic dermatitis. Indeed, 43% of those with early atopic dermatitis were in complete remission by age 3 years. Only 18% had active atopic dermatitis at age 7.
The two predictors of continued atopic dermatitis at age 7 identified in the study were severity of the skin disease and early sensitization to allergens. Moreover, those without concomitant early wheezing were not at increased risk of asthma by age 7, compared with nonwheezers without eczema (J. Allergy Clin. Immunol. 2004;113:92531).
"It's not that there's a progression from atopic dermatitis to asthma, which the atopic march would have us believe, but that there are two distinct phenotypes of eczema early in life: eczema by itself, and eczema plus recurrent wheezing. The two have to be together early in lifeatopic dermatitis and wheezingfor atopic dermatitis to have a bad outcome," Dr. Spahn said.
Recurrent wheezing illnesses affect 35%-70% of children in the first 4 years of life, yet by school age only about 10% of children have active asthma with airway hyperresponsiveness and impaired lung function. What, he asked, distinguishes preschoolers whose wheezing is self-limited from those who will go on to develop asthma?
MAS has shown there are two phenotypes of early childhood wheezers. Those without atopy typically outgrow their wheezing symptoms and have normal lung function at puberty. The majority of those who display sensitization to indoor perennial aeroallergens on skin testing at age 3 years will go on to have active asthma at age 13and their risk is boosted further if they also have a high level of exposure to the allergens. These are the children who need to be on a controller medication, Dr. Spahn explained at the meeting, which was sponsored by the National Jewish Medical and Research Center, Denver.
"If you're able to do [radioallergosorbent testing] or skin testing and you only have one period of time to do it, I would say do it at age 3 because that's the cut point. If you're negative at 3, chances are you're going to outgrow this thing, and if you're positive at 3, chances are you're not," he continued.
Nine of every ten young children with recurrent wheezing but no atopy on skin testing at age 3 lost their respiratory symptoms by school age and continued to have normal lung function by age 13.
In contrast, 56% of atopic wheezers had asthma by age 13. Impairment of small-airway function at age 7 years, as assessed by maximum expiratory flow at 50%, was greater in children sensitized to allergens by age 3 years than in those sensitized by age 5 and greater in those with high rather than low home exposure (Lancet 2006;368:76370).
"The exposure assessment is what makes this study so great. They went to the homes to see whether it was just sensitization in children or sensitization plus exposure that drives the development of asthma," Dr. Spahn observed.