Evaluation of previously patch-tested patients referred to a contact dermatitis clinic

One of the frustrations for clinicians who use patch testing is the patient in whom screening patch tests does not yield a relevant result that improves patient outcome. Is it allergic contact dermatitis? Was an allergen missed? Is the screening allergen relevant after all?

The purpose of this study was to look at the subset of patients referred to a contact clinic who had previously undergone patch testing to seek answers to these questions for this population.

The charts of all 119 physician-referred patients seen in the contact clinic from February through August 1995 were reviewed. Information was gathered about the sites of dermatitis, previous patch testing results, current patch testing results (using the North American Contact Dermatitis Group series and supplemental allergens when indicated), and final diagnosis.

Forty-three patients had previously undergone patch testing. Nineteen had been tested with the True Test and 24 with the screening series presumed to be Hermal. The sites of skin involvement were similar to the untested group (approximately 1/3 hands, 1/3 face/exposed sites, and 1/3 other). Eighteen pretested patients(42%) had been reported to have one or more positive patch tests, with the most frequently reported allergens, including neomycin (4), quaternium 15 (3), Balsam of Peru (3), fragrance (2), and formaldehyde (2). On repeat testing, 77% of the previous positives were again positive, and many were thought to be relevant. Nine of the 18 had additional allergens deemed relevant. Twenty-five pretested patients had been negative on initial patch testing. Eighteen of the 25 (72%) had positive allergens on repeat testing, and most were thought to be relevant. There were 17 reactions to screening allergens and 16 reactions to additional allergens or products. Variations noted with initial negative testing included use of systemic corticosteroids, patient self-removal of tests, and single 48-hour readings. Overall, 27 of 43 pretested patients (63%) were found to have relevant additional allergens with contact clinic evaluation. Screening allergens were underrecognized as being relevant by clinicians in practice.

Patients suspected of having an allergic component to their dermatitis should be patch tested with the screening series of allergens. Interpretation of the relevance of the allergens and appropriate avoidance is a challenge. If screening allergen patch testing is negative or believed to be not relevant in a patient with persistent dermatitis, there may be a high yield on further patch test evaluation.