Patch testing in atopic dermatitis

Reviewed by: Jennifer K Chen, MD, and Susan T Nedorost, MD

Atopic dermatitis (AD), colloquially referred to as eczema, typically presents in children as itchy, dry, scaly patches of skin that appear on the scalp, forehead, and/or face.¹ Symptoms may begin early, developing in infants aged as young as 2 to 3 months. For most people, symptoms of AD present before the age of 5 years, although it occasionally manifests in adolescence or adulthood. It is estimated that 10% to 20% of children worldwide suffer from AD.

Individuals who have AD also may experience allergic contact dermatitis (ACD), which arises from separate pathologic processes. Allergic contact dermatitis is a hypersensitivity reaction resulting from contact sensitization.² Common sources of ACD include poison ivy, poison oak, poison sumac, nickel, fragrances, rubber, and various dyes and additives. Pediatric ACD has become increasingly common, affecting as many as 20% of children. Detecting ACD in patients with AD is important because its presence may serve to exacerbate AD.

Patch testing is a standard part of the diagnostic regimen for ACD. However, patch testing in patients with AD represents a conundrum for clinicians.

As explained to Contemporary Pediatrics by Jennifer K Chen, MD, Department of Dermatology, Stanford University, Redwood City, California, “In the patch testing community, we've noticed that AD patients represent a particularly challenging population. There has been confusion among many practitioners as to what constitutes best practice. Sometimes, these patients are not sent for patch testing at all, which is a shame as many times there may be complicating allergies that we can do something about. When patch testing is being performed, it may not be conducted or interpreted in an optimal manner.”

New guidance for clinicians

To address this knowledge and practice gap, a working group of experts in AD and ACD created the first expert consensus recommendations on patch testing in patients with AD.³ This guidance, which was published this summer in the journal Dermatitis, grew from an interactive session held at the 2014 American Contact Dermatitis Society annual meeting in Denver, Colorado.

The expert consensus statement guides clinicians in determining when and how to perform patch testing in patients with AD, including identification of scenarios in which patch testing would be appropriate. The authors recommend that patch testing be considered in patients with AD who have:

·      dermatitis that fails to improve with topical therapy;

·      atypical/changing distribution of dermatitis, or a pattern suggestive of ACD;

·      therapy-resistant hand eczema (among those in the working population);

·      adult-onset or adolescent-onset AD; and

·      severe or widespread dermatitis, in which case patch testing is recommended before initiating systemic immunosuppressant treatment.

NEXT: Modified patch testing in kids

Patch testing is not likely to be informative for patients with stable, well-controlled AD; those who are currently experiencing an AD flare; or those who have a recent or current exposure to immunosuppressive therapy or ultraviolet radiation. The experts also note that certain medications may lead to false-negative tests, whereas preexisting cutaneous inflammation may cause false-positive test results.

Allergen selection for patch testing should be individualized, taking into account allergens that the patient is likely to encounter based on local environment, avocation, use of personal care products or topical medications, and so on. These allergens may differ in patients with AD from that of the general population.

Susan T Nedorost, MD, Department of Dermatology, University Hospitals Cleveland Medical Center, Cleveland, Ohio, an author on the consensus statement, notes that, “We often see allergy to less potent allergens such as vitamin E and propylene glycol in [patients with AD]. Most of these weaker sensitizers are not routinely patch tested; routine patch tests are composed mostly of potent sensitizers. Failure to patch test to the allergens most relevant for this population has perpetuated the myth that contact allergy does not occur in these patients.”

Modified patch testing for kids

In the pediatric population, patch testing requires some modification to account for differences in patient size and allergen exposure. Chen, first author of the consensus statement, relays her experience, stating that, “In children who are very young, we tend to do targeted testing given the small size of their backs and the often shorter list of potential exposures. We try to avoid patch testing with allergens that may have higher rates of active sensitization if there is no history of exposure to common culprit items that may contain these allergens. Para-phenylenediamine and acrylates are great examples of this. Children 12 and older can be patched tested with a standard screening series the same as adults.”

Interpreting patch testing results in patients with AD can be challenging in that increasing reactivity over time may not occur and the overall response may be weaker. Delayed reading of test results may be beneficial and, for clinicians with limited patch testing experience, referral to an experienced practitioner should be considered. A searchable directory of practitioners who offer patch testing may be found at the American Contact Dermatitis Society website.

By sharing these recommendations, the authors of the consensus document hope to build awareness and improve the appropriate evaluation of ACD in patients with AD.

REFERENCES

1. American Academy of Dermatology. Atopic dermatitis. Available at: https://www.aad.org/public/diseases/eczema/atopic-dermatitis. Accessed on September 28, 2016.

2. Silverberg NB. Pediatric contact dermatitis. Available at: http://emedicine.medscape.com/article/911711. Updated August 22, 2016. Accessed on September 28, 2016.

3. Chen JK, Jacob SE, Nedorost ST, et al. A pragmatic approach to patch testing atopic dermatitis patients: clinical recommendations based on expert consensus opinion. Dermatitis. 2016;27(4):186-192.

Dr Murcia is a medical writer in North Carolina. She has nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article.