Allergic contact dermatitis is the most frequent dermatologic diagnosis in patients with affected anatomical sites adjacent to the scalp vs those with isolated scalp involvement alone, according to study research published in the Journal of the American Academy of Dermatology.

The study was a retrospective cross-sectional analysis of deidentified data from 1996 through 2016 taken from the North American Contact Dermatitis Group. Patients with scalp involvement of 3 or fewer coded anatomic sites, with or without additional sites, were included in this analysis.

Patients were classified into 5 mutually exclusive subgroups based on anatomic area involvement: scalp only (n=505); scalp plus face/ear/neck (S+FEN; n=883); scalp plus eyelids, eyes, lips, face, ears, neck, trunk, and/or arms (S+FENAT; n=388); scalp plus any site(s) other than face, ears, neck, arms, or trunk (S+Any; n=555); and scalp not specifically coded as a site (n=46,422).

Approximately 4.8% (n=2331) of patients had scalp identified as 1 of up to 3 anatomic sites affected. Of these patients, 21.7% (n=505) had scalp only, 37.9% had S+FEN, 16.6% (n=388) had S+FENAT, and 23.8% (n=555) had S+Any.


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In scalp-only patients, 38.6% of primary diagnoses were for allergic contact dermatitis, followed by 17.2% for seborrheic dermatitis, 16.4% for other dermatoses, 13.5% for other dermatitis, and 9.3% for irritant contact dermatitis. A primary diagnosis of allergic contact diagnosis was more frequent for patients in the S+FEN (59.6%), S+FENAT (51.8%), and S+Any (53.9%) groups. The most frequent clinically relevant allergen in patients with scalp-only involvement included p-phenylenediamine, fragrance mix I, nickel sulfate, balsam of Peru, and cinnamic aldehyde.

Sensitivity to methylisothiazolinone was most pronounced in patients with involvement of anatomical sites adjacent to the scalp. Hair dyes, shampoos and conditioners, and various consumer items were the top 3 identified sources of scalp-only allergens.

A limitation of the study was the inclusion of patients who were patch tested at tertiary referral centers, which may reduce the generalizability of the findings across the general population as well as the general dermatology population.

Based on their findings, the investigators concluded that “patch testing for scalp signs/symptoms should be considered for individuals with a suggestive history (dye use) or involvement of adjacent anatomical areas.”

Reference

Warshaw EM, Kullberg SA, DeKoven JG, et al. Scalp involvement in patients referred for patch testing: Retrospective cross-sectional analysis of North American Contact Dermatitis Group data, 1996 to 2016. Published online August 18, 2020. J Am Acad Dermatol. doi:10.1016/j.jaad.2020.08.046