Patching Psoriasis

Patch testing is one of the major diagnostic tools in the evaluation of allergic contact dermatitis. One limitation of patch testing is the use of steroids prior to testing. Because steroids may suppress a positive test reaction, the use of topical steroids on the test site or oral steroids should be discontinued for at least 2 weeks prior to testing. Therefore, it is interesting to consider the effect of biologics on the reliability of patch testing.

Kim et al (Dermatitis. 2014;25:182-190) evaluated the prevalence of positive patch tests in psoriasis patients receiving biologics and whether these results differed from those of psoriasis patients who were not receiving biologics. An institutional review board–approved retrospective chart review was performed for individuals with psoriasis who were patch tested from January 2002 to 2012 at Tufts Medical Center in Boston, Massachusetts. Patients were selected if they had a history of psoriasis, psoriatic arthritis, and patch testing as identified by International Classification of Diseases, Ninth Revision, codes 696.1, 696.0, and 95044, respectively, in their medical records. Patients were patch tested using a modified North American Contact Dermatitis Group standard and cosmetics series. Readings were performed at 48 hours and 72 to 96 hours. The North American Contact Dermatitis Group grading system was used to grade reactions.

The chart review included 15 psoriasis patients who were on biologics (cases) and 16 psoriasis patients who were not on biologics (control subjects). The biologics used were ustekinumab (n=7), etanercept (n=4), adalimumab (n=3), and infliximab (n=1). The authors determined that 80% (12/15) of cases had at least 1 positive reaction compared with 81% (13/16) of control subjects, 67% (10/15) of cases had 2+ positive reactions compared with 63% (10/16) of control subjects, and 27% (4/15) of cases had 3+ positive reactions compared with 38% (6/16) of control subjects. These differences were not statistically significant.

Given the limitation of the small number of patients evaluated, the authors concluded that biologics do not appear to influence the abilities of patients with psoriasis to mount a positive patch test.

What’s the issue?

This study is small, but the findings do give an indication that the biologic agents utilized for psoriasis do not suppress patch test reactions. These data are not typically what we collect in this population, but it is nice to know. What has been your experience in patch testing patients on biologic therapy?

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