Three case series of inverted follicular keratosis on the nose mimicking basal cell carcinoma.

Inverted follicular keratosis (IFK) is considered an irritated type of seborrheic keratosis, originating from the follicular infundibulum. We herein describe 3 cases of IFK. The first case involved a 23­year­old woman who had a black nodule located on the dorsum of the nose measuring 2­3 mm in diameter that had been present for approximately 1 year. The second case involved an 85­year­old man with a similar lesion that had been present for approximately half a year. The third case involved a 45­year­old man with a similar lesion that had been present for approximately 2 months. The suspected diagnosis, based on clinical and dermoscopic examinations, was basal cell carcinoma (BCC). Excisional biopsies were performed in all 3 cases. The histopathological examination of the biopsy specimens revealed no evidence of BCC; rather, the downward growth of the epithelium, with a number of squamous eddies, was noted. Based on these findings, we diagnosed the patients with IFK. It was not possible to discriminate between IFK and BCC based on the clinical and dermoscopic findings. When physicians encounter a black lesion on the nose similar in appearance to that of BCC, it is important to include IFK in the differential diagnosis.