Evidence suggests that a strong positive correlation exists between atopic disease and attention-deficit/hyperactivity disorder. But since all studies of the issue to date have been observational, "a causal relationship cannot be inferred," according to a research commentary in the August issue of the Archives of Dermatology.
"Further epidemiologic studies that use consistent and validated measures to more accurately define atopic disease and ADHD and adjust for confounders and disease severity are needed to better elucidate this relationship," said Dr. Sarah N. Gee and Dr. Michael Bigby of the departments of dermatology at Harvard Medical School and Beth Israel Deaconess Medical Center, both in Boston (Arch. Dermatol. 2011;147:967-70).
Dr. Gee and Dr. Bigby commented on a review of the literature presented by Dr. Jochen Schmitt and colleagues in the journal Allergy, which was titled: "Is atopic disease a risk factor for attention-deficit/hyperactivity disorder?" A systematic review (Allergy 2010;65:1506-24). That review covered 20 studies – 1 cohort study, 2 case-control studies, and 17 cross-sectional studies – involving 170,175 patients with eczema, asthma, rhinitis, or atopic dermatitis who also had ADHD symptoms. The studies reviewed had been conducted around the world, including in Germany and in other parts of Europe, and in North America, Australia, and New Zealand. All except one of the studies focused on children and adolescents.
"Four of the six studies that investigated eczema and ADHD found a statistically significant positive association, two with an odds ratio greater than four. Two of the three studies that used multivariate logistic regression for confounding factors found a statistically significant positive relationship between atopic dermatitis and ADHD. [And] with respect to asthma, all 12 studies that investigated asthma and ADHD reported a positive association ([odds ratio], 1.23-2.42)," Dr. Gee and Dr. Bigby said.
However, two studies that examined a possible link between allergic rhinitis and ADHD found no correlations.
The review by Dr. Schmitt fulfilled most of the criteria laid out by the Centre for Evidence-Based Medicine’s guidelines for "a useful and valid review." The choice of articles to include was appropriate, and the data were sufficient to answer the clinical question they posed.
The review was restricted to studies published in English or German, which might have left out some relevant studies. "However, we replicated their search without language restriction and found no additional studies," Dr. Gee and Dr. Bigby reported.
The review included searches of two databases, but Dr. Gee and Dr. Bigby found two additional relevant studies when they searched additional databases. Both of these were observational studies, and both found a significant association between atopic dermatitis and ADHD symptoms, they noted.
The most important criticism of the review by Dr. Schmitt is that assessment of both atopic disease and ADHD was inconsistent across the various studies, and tended to rely on parent reporting rather than physician diagnoses. For example, only 1 of the 20 articles used Diagnostic and Statistical Manual criteria for an ADHD diagnosis.
Such shortcomings should be addressed in any future research of the issue, Dr. Gee and Dr. Bigby said.
No financial conflicts of interest were reported.