The identification of trichoscopic features of allergic scalp contact dermatitis: a pilot-study of a single center

BACKGROUND: Very few reports have described trichoscopic patterns of allergic scalp contact dermatitis (ASCD), which is usually an exclusion diagnosis on hair disorders. Trichoscopy is a simple, diffused method for investigating scalp diseases and may help to establish the characteristic findings of ASCD. METHODS: A retrospective chart review was conducted on patients who visited the outpatient hair consultation at the Department of Experimental, Diagnostic, and Specialty Medicine of the University of Bologna, Italy, from January 2020 to September 2021. The inclusion criteria were based on the previous diagnosis of ASCD, patch test positivity; recover after allergen suspension and absence of other scalp diseases besides androgenetic alopecia on the patients in use of topical minoxidil. All trichoscopic features were described. RESULTS: ASCD was observed in 12 patients. The allergens were as follows: topical minoxidil (58.33%), p-phenylenediamine (PFD) (33.33%), wig, nickel, methylchloroisothiazolinone, and methylisothiazolinone (MCI/MI-Kathon CG) in one patient each, with multiple positive patients. Scales were classified as diffuse, patchy, white, and yellowish, and vascular patterns were classified as arborizing vessels, twisted red loops, simple red loops, bushy red loops, red dots, and globules besides atypical vessels. The main findings were erythema (100%), white scales (100%), arborizing vessels (91.2%), and simple red loops (91.2%). CONCLUSIONS: Trichoscopy is a useful tool to help on the diagnosis of ASCD.