When AD is really contact dermatitis.
Clinical signs of contact dermatitis include lesions with an atypical distribution/pattern, such as head, eyelid, or cheilitis/perioral predominance, or lesions on the hand or foot. Also elevate your suspicion in patients with therapyresistant hand eczema, adult- or childhood-onset atopic dermatitis without childhood eczema, as well as in cases of severe or widespread dermatitis prior to initiating a systemic immunosuppressant. The list of potential allergens to consider includes metal (especially nickel, cobalt, and potassium dichromate), fragrances such as formaldehyde and balsam of Peru, and preservatives, as well as topical emollients, corticosteroids, antibiotics, and antiseptics.
If you choose to perform patch testing, the hypothetical detection rate of the Thin-Layer Rapid Use Epicutaneous Patch (T.R.U.E. test) (TT), compared with the North American Contact Dermatitis Group screening series is 69.7%-75.1%. Antigens on the TT but not on the NACDG series include thimerosal, gold, and quinoline mix. The TT also has a higher false-positive rate to neomycin, thiuram mix, balsam of Peru, fragrance mix, cobalt, and lanolin.
Dr. Fonacier, professor of medicine at the State University of New York at Stony Brook and section head of allergy at Winthrop University Hospital, Mineola, N.Y., recommends loading acrylates, fragrances, and allergens in an aqueous vehicle immediately before application. She noted that delayed patch test readings are common to metals, topical antibiotics, and topical corticosteroids, and that positive reactions to gold are often not clinically relevant. "The patch test positivity of gold can be as high as 30% in adults and a little bit less in children, but results from two large studies show clinical relevance in only 10%-15% of cases," she said. A trial of gold avoidance may be warranted in patients with suspected jewelry allergy, facial or eyelid dermatitis, or exposure through gold dental restorations.
She went on to share tips for reading skin patch tests. The first reading should be done after 48 hours, while the second should be done 3, 4, or 7 days after application. "The second reading helps distinguish irritant from allergic responses," she said. "Thirty percent of negative tests at 48 hours may be positive on delayed readings." Most true allergic reactions occur between 72 and 96 hours. Allergens that may peak early include thiuram mix, carba mix, and balsam of Peru. Those that disappear after 5 days include balsam of Peru, benzoic acid, disperse blue #124, fragrance mix, mercury, methyldibromo glutaronitrile, phenoxyethanol, and octyl gallate. Delayed patch test reactions after 5 days include metals (gold potassium dichromate, nickel, and cobalt), topical antibiotics (neomycin and bacitracin), and topic corticosteroids.
Dr. Fonacier disclosed that she has received research and educational grants from Baxter and Genentech. She is also a consultant to Church and Dwight and Regeneron.
BY DOUG BRUNK
Expert Analysis at the 2017 AAAAI Annual Meeting
COMMENTARY BY DR. SIDBURY
* Is it eczema or allergic contact dermatitis? Yes! It is instructive to remember that allergic contact dermatitis is a type of eczema, and just looking at the morphologic or even histologic features of a rash cannot necessarily distinguish one from the other. Dr. Luz Fonacier instead points to abrupt flares, changes in pattern or distribution, or an immediate rebound after treatment as clues to a potential contact trigger. She details a number of potential allergens that can be in myriad OTC and prescription products, many used putatively to help the rash. This is a set-up for missed diagnosis and ever-escalating therapeutic intensity. In cases of refractory dermatitis, particularly if systemic therapy is considered, Dr. Fonacier recommends patch testing to rule out a delayed type IV hypersensitivity reaction; although logistically cumbersome, it can be quite rewarding when a culprit allergen is identified.
DOUG BRUNK/FRONTLINE MEDICAL NEWS
Caption: Dr. Luz Fonacier offered tips for reading skin patch tests of the AAAAI meeting.