Children with atopic dermatitis (AD) were significantly more likely to have positive patch test results than were children without AD according to a study of over 900 children evaluated for allergic contact dermatitis (ACD) with patch testing, a finding that investigators say underscores the value of considering ACD in patients with AD and referring more children for testing.

Dr JiaDe Yu

ACD is under-detected in children with AD. In some cases, it may be misconstrued to be AD, and patch testing, the gold standard for diagnosing ACD, is often not performed, said senior author JiaDe Yu, MD, MS, a pediatric dermatologist and director of contact and occupational dermatology at Massachusetts General Hospital in Boston, and his co-authors, in the study, published on September 24 in the Journal of the American Academy of Dermatology.

Yu and his colleagues utilized a database in which dermatologists and allergists (mainly dermatologists), all of whom had substantive experience in patch testing and in diagnosing and managing ACD in children, entered information about children who were referred to them for testing.

Of 912 children referred for patch testing between 2018 and 2022 from 14 geographically diverse centers in the United States (615 with AD and 297 without AD), those with AD were more likely to have more than one positive reaction (odds radio [OR], 1.57; 95% CI, 1.14-2.14; P = .005) and had a greater number of positive results overall (2.3 vs 1.9; P = .012).

AD and ACD both present with red, itchy eczema-like patches and plaques and can be “really hard to differentiate,” Yu said in an interview.

“Not everybody with AD needs patch testing,” he said, “but I do think some [patients] who have rashes in unusual locations or rashes that don’t seem to improve within an appropriate amount of time to topical medications. These are the children who probably should have patch testing.”

Candidates for patch testing include children with AD who present with isolated head or neck, hand or foot, or anal or genital dermatitis, Yu and his colleagues write in the study. In addition, Yu said in the interview, “if you have a child who has AD that involves the elbow and back of the knees but then they get new-onset facial dermatitis, say, or new-onset eyelid dermatitis…there’s [significant] value in patch testing.”

Children with AD in the study had a more generalized distribution of dermatitis and were significantly less likely to have dermatitis affecting the anal or genital region, the authors note in the study.

Asked to comment on the results, Jennifer Perryman, MD, a dermatologist at UCHealth in Greeley, Colorado, who performs patch testing in children and adults, said that ACD is indeed “often underdiagnosed” in children with AD, and that the study “solidifies” the importance of considering ACD in this population.

“Clinicians should think about testing children when AD is [not well controlled or] is getting worse, is in an atypical distribution, or if they are considering systemic treatment,” she said in an e-mail.

“I tell my patients, ‘I know you have AD, but you could also have comorbid ACD, and if we can find and control that, we can make you better without adding more to your routine, medications, etc.'” said Dr Perryman, who was not involved in the research.

Top Allergens

The top 10 allergens between children with and without AD were largely similar, the authors of the study report. Nickel was the most common allergen identified in both groups, and cobalt was in the top five for both groups. Fragrances (including hydroperoxides of linalool), preservatives (including methylisothiazolinone [MI]), and neomycin ranked in the top 10 in both groups, though prevalence differed.

MI, a preservative frequently used in personal care products and in other products like school glue and paint, was the second most common allergen identified in children with AD. Allergy to MI has “recently become an epidemic in the United States, with rapidly increasing prevalence and importance as a source of ACD among both children and adults,” the authors note.

Children with AD were significantly more likely, however, to have ACD to bacitracin (OR, 3.23; P = .030) and to cocamidopropyl betaine (OR, 3.69; P = .0007) the latter of which is a popular surfactant used in “baby” and “gentle” skincare products. This is unsurprising, given that children with AD are “more often exposed to a myriad of topical treatments,” Yu and his colleagues write.

And although not a top 10 allergen for either group, ACD to “carba mix,” a combination of three chemicals used to make medical adhesives and other rubber products (such as pacifiers, toys, school supplies, and rubber gloves) was significantly more common in children with AD than in those without (OR, 3.36; P = .025).

Among other findings from the study: Children with AD were more likely to have a longer history of dermatitis (4.1 vs 1.6 years, P < .0001) prior to patch testing. Testing occurred at a mean age of 11 and 12.3 years for children with and without AD, respectively.

The number of allergens tested and the patch testing series chosen per patient were “not statistically different” between the children with and without AD, the researchers report.

Patch Testing Availability

Clinicians may be hesitant to subject a child to patch testing, but the process is well tolerated in most children, Perryman said. She uses a modified panel for children that omits less relevant allergens and usually limits patch testing to age 2 years or older due to a young child’s smaller surface area.

Yu, who developed an interest in patch testing during his residency at the Medical College of Wisconsin, Milwaukee, where he worked with a patch-testing expert, will test children as young as 3-4 months with a “small selection of patches.”

The challenge with a call for more patch testing is a shortage of trained physicians. “In all of Boston, where we have hundreds of dermatologists, there are only about four of us who really do patch testing. My wait time is about 6 months,” said Yu, who is also an assistant professor at Harvard Medical School.

Allergists at Massachusetts General Hospital do “some patch testing…but they refer a lot of the most complicated cases to me,” he said, noting that patch testing and management of ACD involves detailed counseling for patients about avoidance of allergens. “Overall dermatologists represent the largest group of doctors who have proficiency in patch testing, and there just aren’t many of us.”

Perryman also said that patch testing is often performed by dermatologists who specialize in treating ACD and AD, though there seems to be “regional variance” in the level of involvement of dermatologists and allergists in patch testing.

Not all residency programs have hands-on patch testing opportunities, Yu said. A study published in Dermatitis, which he co-authored, showed that in 2020, 47.5% of dermatology residency programs had formal patch testing rotations. This represented improvement but is still not enough, he said.

The American Contact Dermatitis Society offers patch-testing mentorship programs, and the American Academy of Dermatology has recently begun offered a patch testing workshop at its annual meetings, said Yu, who received 4 weeks of training in the Society’s mentorship program and is now involved in the American Academy of Dermatology’s workshops and as a trainer/lecturer at the Contact Dermatitis Institute.

The study was supported by the Dermatology Foundation. Yu and his co-investigators reported no conflicts of interest. Perryman had no disclosures.

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