Abstract: 【Abstract】 Objective To analyze dermoscopic and reflectance confocal microscopic characteristics of acanthosis nigricans, and to assess the value of dermoscopy and reflectance confocal microscopy （RCM） in the auxiliary diagnosis of acanthosis nigricans. Methods A total of 63 patients with acanthosis nigricans were collected from Department of Dermatology, the Third People′s Hospital of Hangzhou from January 2018 to December 2019, and 5 healthy individuals served as controls. Two lesions on the neck and axilla were examined with dermoscopy and RCM respectively in each patient. Biopsies were carried out at the sites evaluated by dermoscopy and RCM in 3 patients, followed by routine histopathological examination. Results Dermoscopy showed papilloma-like hyperplasia in 126 （100%） lesions, "fat finger" structures in 119 （94.4%）, and "gully" structures in 120 （95.2%）. RCM showed hyperpigmentation in the basal layers, downward extension and twisting of dermal papillary rings and "gully" structure in 126 （100%） lesions, moderately to highly refractive particles in the dermal papillary rings in 87 （69.0%）. Conclusion Acanthosis nigricans has typical dermoscopic and reflectance confocal microscopic characteristics, which can provide a basis for its diagnosis and differential diagnosis.

Key words: Acanthosis nigricans, Dermoscopy, Microscopy, confocal