Prevalence and Trend of Allergen Sensitization in Patients with Nummular (Discoid) Eczema Referred for Patch Testing, North American Contact Dermatitis Group Data, 2001-2016.

Background Few studies examined the relationship between nummular (discoid) eczema (NE) and allergic contact dermatitis (ACD). Objective To examine the trends, associations, and clinical relevance of ACD in NE patients referred for patch testing. Methods Retrospective analysis of 38,723 patients from the North American Contact Dermatitis Group. Results Overall, 748 (1.9%) patients were diagnosed with NE; 23.9% had a concomitant diagnosis of ACD. The prevalence of NE fluctuated over time between 2001-2016, with no overall change in prevalence in diagnosed NE. In multivariable logistic regression models, NE steadily increased with age and was associated with male sex, Asian and other race/ethnicity, and inversely associated with a history of AD and hay fever. Patients with NE had lower proportions of ≥1 positive allergic reaction and lower odds of a positive reaction in multiple, individual allergens. The most commonly relevant allergens in patients with NE were formaldehyde 2.0% aq., methylisothiazolinone, quaternium-15, fragrance mix I, and propylene glycol. Conclusion NE is a heterogeneous disorder with distinct subsets of lesional distribution and profile of relevant allergens, especially formaldehyde and formaldehyde releasers. Nearly 1 in 4 NE patients had ACD, supporting the role of patch testing in NE patients. This article is protected by copyright. All rights reserved.