SAN FRANCISCO Allergic contact dermatitis looks like other forms of dermatitis, but the history and some visual clues can help make the diagnosis, Dr. Anna L. Bruckner said at a meeting sponsored by Skin Disease Education Foundation.
A history of exposure to common contact allergens, such as a recent run-in with poison ivy, poison oak, or poison sumac, may be all that is needed. A history of contact with other common allergens provides support for suspicions of allergic contact dermatitis. These allergens include nickel and topical antibiotics such as neomycin, gentamicin, and bacitracin.
In addition, said Dr. Bruckner of the pediatric dermatology clinic at Lucile Packard Children's Hospital in Palo Alto, Calif., the following "four P's" point to allergic contact dermatitis in children:
▸ Persistence. A rash that "doesn't respond to therapy like you would expect"coming back time and again in the same place despite treatment with topical steroidsmay be an allergic contact dermatitis, she said.
An allergic contact dermatitis begins 1224 hours after exposure to the allergen, peaks at 35 days, and may last 34 weeks if untreated.
▸ Place. A rash that is localized to an area not considered a typical location for dermatitis should raise suspicion, especially if an area where contact with a suspected allergen could be imagined.
Allergic contact dermatitis on a child's face or eyelids is caused most commonly by neomycin; fragrances; preservatives in creams, soaps or shampoos; or thimerosal in eyedrops. Nickel (in jewelry or jeans fasteners) is the most common cause of allergic contact dermatitis in the infraumbilical area and on the earlobes, neck, and wrists.
Compounds used in rubber production can produce allergic responses in the waistband area or on the dorsum of the feet, where leather also is a suspect because of an agent used in leather tanning. In the axillae, preservatives or fragrances in deodorant may cause allergic dermatitis.
▸ Pattern. Think of allergic contact dermatitis when there is a distinct pattern of eruption that is unusual for dermatitis, such as a linear rash. Dermatitis that is localized to the face, or that appears symmetrically on earlobes or on the dorsum of the hands or feet, may be a tip-off to allergic contact dermatitis.
Dr. Bruckner described a 7-year-old patient with a several-year history of a ring-shaped eruption on the posterior thighs and upper buttocks, which is "an area that we don't typically think about with atopic dermatitis." The rash cleared repeatedly with topical steroids but always returned, except for a rash-free summer he spent in India. This was toilet-seat dermatitis, a relatively common reaction to wood toilet seats that is caused by either the lacquer in the seat or the resin in the wood itself.
▸ Patch testing. If the etiology isn't apparent, epicutaneous patch testing may help determine whether allergic contact dermatitis is the culprit.
Besides nickel, preservatives, fragrances, rubber products, and leather, other common contact allergens include topical antibiotics (neomycin, bacitracin, and gentamicin); lanolin used in cosmetics; disperse dyes used to color the elastic waistbands of disposable diapers; and p-phenylenediamine (a component of hair dye, temporary tattoos, and hennalike products).
Allergic contact dermatitis may account for up to 20% of all cases of childhood dermatitis, although the exact incidence and prevalence are unknown. It can occur at all ages but is relatively uncommon in younger children; the prevalence increases as children age and have more exposures to potential allergens, she said.
Studies of asymptomatic children suggest that up to 25% are sensitized to one of several common contact allergens. Among children with dermatitis, up to 60% will have positive patch test reactions, studies suggest, but "whether or not those are clinically relevant is unclear," Dr. Bruckner noted.
Topical corticosteroids are the mainstay of treatment, but systemic steroids may be needed if the rash covers more than 10% of skin surface. With either option, treating for a full 23 weeks is important to avoid rebound dermatitis.
SDEF and this news organization are wholly owned subsidiaries of Elsevier.
A ring-shaped pattern on the posterior thighs and buttocks is consistent with allergic reaction to a wooden toilet seat. COURTESY DR. ANNA L. BRUCKNER