Xiaolin Bu,1,* Liwei Feng,2,* Jing Guo,3 Rongzhu Yu,2 Xinling Bi4 

1Laboratory of Laser and Medical Innovation Application, Department of Dermatology, Gongli Hospital of Shanghai Pudong New Area, Shanghai, People’s Republic of China; 2School of Gongli Hospital Medical Technology, University of Shanghai for Science and Technology, Shanghai, People’s Republic of China; 3Postgraduate Training Base at Shanghai Gongli Hospital, Ningxia Medical University, Shanghai, People’s Republic of China; 4Department of Dermatology, Changhai Hospital, Naval Medical University, Shanghai, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Xinling Bi, Department of Dermatology, Changhai Hospital, Naval Medical University, 168 Changhai Road, YangPu District, Shanghai, People’s Republic of China, Email bixinling@163.com

Abstract: A 65-year-old Asian male presented with a circular skin lesion on the flexor aspect of the right calf that first appeared at age 13 and gradually expanded peripherally. Six months prior to presentation, a dark brown, horn-like keratotic lesion with a hard texture emerged on the annular lesion, growing progressively without pain or pruritus. The cutaneous horn was surgically excised, and the annular lesion underwent biopsy. Pathological findings revealed abundant mucin in dermal collagen, dense histiocyte infiltration, and focal mild collagen degeneration, confirming a diagnosis of granuloma annulare complicated by a cutaneous horn.

Keywords: cutaneous horn, granuloma annulare, keratotic