Development of a Cutaneous Horn on a Lower Extremity with Granuloma Annulare: A Rare Co-Occurrence.

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.