Abstract
INTRODUCTION: Although recognition of prurigo nodularis (PN) and lichen simplex chronicus (LSC) of the scalp is usually straightforward, they may sometimes pose difficulties in terms of differential diagnosis with other similar dermatoses. The aim of this observational retrospective study was to assess dermoscopic features of PN and LSC of the scalp across fair- and dark-skinned individuals and compare them with those of clinical mimickers. METHODS: Fair-skinned (Fitzpatrick phototypes I-III) and dark-skinned (Fitzpatrick phototypes IV-VI) patients with a histological diagnosis of PN/LSC of the scalp, along with controls, were considered. All the images were randomly evaluated by two independent investigators to identify findings according to standardized criteria. Interobserver agreement was evaluated through Cohen's kappa coefficient, while Fisher's exact test with p value set at 0.01 was used for comparative analyses between cases and controls. RESULTS: The study included 79 cases, including 40 instances of PN/LSC of the scalp (27 with fair skin and 13 with dark skin) and 39 controls. The most common dermoscopic findings (> 1/3 of cases) of PN/LSC in both light and dark phototypes included sparse follicular plugs, broken hairs, purple structureless areas, broom-like hairs, and erosions. Additionally, purple dots, perivascular white halo and dotted vessels with unspecific distribution were also common in fair skin, while white lines (peripheral-radial) and structureless areas turned out to be as frequent in dark skin. Comparative analysis showed that dotted vessels, follicular plugs, broken hairs, broom-like hairs, purple structureless areas, and perivascular white halo were more common compared to control in light phototypes, whereas only erosions, peripheral white lines, and purple structureless areas reached statistical significance in dark-skinned patients (p < 0.01). Kappa values were 0.88 and 0.81 for fair and dark skin, respectively. CONCLUSION: Dermoscopy is a valuable adjunct in the non-invasive diagnosis of PN and LSC of the scalp, with good reproducibility across skin phototypes.