Immediate ex‐vivo dermoscopy of a nail bed biopsy specimen – a useful procedure for melanonychia

bulocystic squamous cell carcinoma as a differential diagnosis. Infundibulocystic squamous cell carcinoma which is known to have the distinctive histopathological features of numerous microor dilated infundibular cysts with minimal cytological atypia that infiltrate and penetrate deep into the underlying tissue. In our case, the tumour cells without evident nuclear atypia did not penetrate in the deep dermis and clinical manifestation of which present symmetrical, exophytic and central erosion. Furthermore, long-standing history indicated the benign lesion, so we excluded infundibulocystic squamous cell carcinoma. The dermoscopic features of millia-like cysts often resemble those of seborrhoeic keratosis; however, in our case, typical dermoscopic features of seborrhoeic keratosis, such as comedolike openings, fingerprint-like structures and brain-like appearances, were not observed. We regarded the lack of brownish background as a unique characteristic. We think these features, especially the multiple millia-like cysts on a background of reddish plaques, might be helpful in the clinical diagnosis of keratoacanthoma en plaque. In conclusion, this is the first report to describe the dermoscopic features of keratoacanthoma en plaque with infundibulocystic hyperplasia. When we encounter reddish plaques with ‘millia-like cysts on an erythematous background’ in dermoscopy, we must consider keratoacanthoma en plaque with infundibulocystic hyperplasia as a differential diagnosis.