Different clinical phenotypes of nail abnormalities in patients with severe atopic dermatitis: a single-centre cross-sectional study

Introduction
Nail involvement in atopic dermatitis (AD) remains an underrecognized and understudied manifestation, despite its potential to significantly contribute to disease burden.

Aim
This study objective was to characterize the prevalence, types, and patterns of nail abnormalities in patients with severe AD and to explore clinical factors associated with their occurrence.

Material and methods
This single-centre, cross-sectional study included adult patients with severe AD (EASI > 21) diagnosed according to the Hanifin and Rajka criteria. Demographic, clinical, and laboratory data were collected, and hand nails were examined for abnormalities. Statistical analyses included Fisher’s exact test, c² test, Mann-Whitney U test, Kruskal-Wallis test with post-hoc Bonferroni correction, Spearman’s correlation, principal component analysis (PCA), and hierarchical clustering. Multiple comparisons were controlled using the Benjamini-Hochberg procedure.

Results
Forty-seven participants (28 males, median age 37.0 years) were included. Glossy nails were the most frequent abnormality (94%), followed by paronychia (40%) and Beau’s lines (36%). Higher EASI scores were significantly associated with Beau’s lines, onychomadesis, eczema of nail folds, petechiae, and paronychia (pBH < 0.05). Correlation analysis revealed strong associations between paronychia and Beau’s lines (R = 0.73), eczema (R = 0.61), and petechiae (R = 0.43). PCA and clustering identified three phenotypic subgroups: destructive-type, mild-type, and onychoschisis-type. The destructive-type was associated with older age and more severe disease.

Conclusions
Nail abnormalities are highly prevalent in severe AD and closely related to disease severity. Distinct phenotypic patterns of nail involvement may reflect varying degrees of structural damage and could have implications for clinical management. Systematic nail assessment should be incorporated into routine AD evaluation.