The Dermoscopic Step-Like Border in Circumscribed Hypokeratosis: A Case Involving the Finger and Literature Reappraisal Across Palmar, Plantar, and Digital Lesions.

Abstract

Circumscribed hypokeratosis is a rare acquired disorder characterized clinically by a sharply demarcated, slightly depressed erythematous patch and histopathologically by abrupt thinning of the stratum corneum. Although initially described on the palm, similar lesions have been reported on the sole, fingers, and other acral sites, generating site-based terms such as circumscribed palmar, plantar, acral, and digital hypokeratosis. Across these presentations, peripheral dermoscopic findings have been variously described as stair-step, step-ladder, rim-like, or geological-strata appearances; however, their consistency across acral sites and their significance relative to other dermoscopic findings have not been specifically reappraised. Here, prompted by a finger lesion with a distinct dermoscopic step-like border, we reappraised previously reported cases with dermoscopic documentation to assess the consistency of this border finding across acral sites and its significance relative to other dermoscopic features. Among 24 previously reported dermoscopy-documented cases, a step-like peripheral border was identified in 22, whereas associated dermoscopic findings varied considerably among reports. The present dorsal finger case further illustrates that this border phenomenon can occur outside classical palmoplantar presentations. These observations suggest that peripheral border architecture may represent a more consistently reported dermoscopic feature than any single associated finding and may aid recognition of circumscribed hypokeratosis.