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Patch Testing to Diphenylguanidine by the North American Contact Dermatitis Group (2013-2016)
Erin M Warshaw1, Rachit Gupta, Joel G Dekoven
1From the *Department of Dermatology, Park Nicollet Health Services †Department of Dermatology, University of Minnesota ‡Department of Dermatology, Minneapolis Veterans Affairs Medical Center §University of Minnesota Medical School, Minneapolis ∥Division of Dermatology, Sunnybrook Health Sciences Centre, University of Toronto, Ontario, Canada ¶Division of Dermatology, University of Louisville, KY **Department of Dermatology, The George Washington University School of Medicine and Health Sciences, Washington, DC ††Department of Dermatology, Duke University, Durham, NC ‡‡Department of Dermatology, Cleveland Clinic, OH §§Department of Dermatology, University of Wisconsin School of Medicine and Public Health, Madison ∥∥Department of Dermatology, University of California San Francisco ¶¶Division of Dermatology, Montreal General Hospital, McGill University, Quebec, Canada ***Department of Dermatology, Columbia University, New York, NY †††Department of Dermatology, Keck School of Medicine, Los Angeles, CA ‡‡‡Division of Dermatology, University of Ottawa, Ontario, Canada §§§Department of Dermatology, Pennsylvania State University, State College ∥∥∥Department of Dermatology, Dartmouth-Hitchcock Medical Center, Lebanon, NH ¶¶¶Department of Specialty Medicine, Ohio University, Columbus.
Background/Objectives:
Carba mix (CM, 3% petrolatum) contains 1,3-diphenylguanidine (DPG, 1%), zinc diethyldithiocarbamate (1%), and zinc dibutyldithiocarbamate (1%). Because DPG is a component of CM, DPG is often not tested separately. The purpose of this study was to determine the frequency of concomitant reactions to CM and DPG.
Methods:
A retrospective analysis of the 2013-2016 North American Contact Dermatitis Group data was conducted. The study group consisted of patients with final interpretation of "allergic" to either DPG or CM. Reactions coded as irritant or doubtful/macular erythema (+/- and not interpreted as allergic) were excluded.
Results:
A total of 10,457 patients were patch tested to both CM and DPG, and 610 (5.8%) had allergic reactions to either CM or DPG (CM only [n = 292, 47.9%], DPG only [n = 190, 31.1%], both [n = 128, 21.0%]). A total of 39.4% of CM-allergic patients reacted to DPG, and 59.7% of DPG-allergic patients reacted to CM. Analyses found that 25% (++/+++ subgroup) to 40% (all patients) of allergic reactions to DPG would have been missed by testing to CM alone. More than 70% of reactions to CM and DPG were +/- or +.
Conclusions:
Patch testing to CM will miss 25% to 40% of positive reactions to DPG. Both CM and DPG have a high frequency of +/- and + reactions.