Background: Circumscribed palmar or plantar hypokeratosis (CPH) is a rare skin disorder only recently described. Objective: To determine the diagnostic features and to provide insight into the pathogenesis of CPH, with analysis of two new Japanese cases. Methods: Dermoscopy, immunohistochemistry, electron microscopy, polymerase chain reaction amplification for human papillomavirus (HPV) DNA and 16S microbial rRNA gene profiling were conducted. Results: Dermoscopy showed characteristic features using both dry and jelly immersion observation; step-like desquamation and a homogeneous erythema with regularly distributed whitish spots. Immunohistochemistry revealed strong staining with anti-pankeratin antibody (AE1+AE3) and anti-keratin 16 antibody, and decreased expression of keratin 2e. EM revealed a breakage of the corneocytes within their cytoplasm, but structures for cell attachment were intact. HPV and lesion-specific bacteria were not detected. Limitations: The number of cases analyzed was two. Conclusion: Hyperproliferative epidermal state along with enhanced corneocyte fragility may account for the unique features in CPH.
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