Eruptive Keratoacanthoma en Plaque Confirmed by Complete Spontaneous Regression: A Case Report and Review of the Literature

Here we present a case of an unusual variant of keratoacanthoma, eruptive keratoacanthoma en plaque, occurring on the upper lip of a 58-year-old man. The lesion was a flesh-colored nodular plaque measuring 1.5×1.0 cm that rapidly grew within 2 months. After two biopsies, the cutaneous lesion grew more rapidly for 1 month, covering the entire cutaneous surface of the upper lip and measuring 6.0×2.0 cm. Thereafter, it disappeared without any treatment within 3 months, resulting in mild scarring with a cobblestone-like surface similar to the stereotypical involuting course of ordinary keratoacanthoma. In addition to the clinical features, the present case displayed essential diagnostic features of eruptive keratoacanthoma by showing typical spontaneous involution not reported in previous reports. Furthermore, it also revealed histopathology suggestive of squamous cell carcinoma, at least focally in addition to that of keratoacanthoma, which may evoke the potential for a misdiagnosis of malignancy. (Korean J Dermatol 2019;57(9):544∼547)