A case of subungual poroma

Abstract

Poromas are benign adnexal tumors most commonly present on the lower extremities, especially in the palmoplantar area among middle-aged individuals. They rarely appear under the nails, where fewer sweat glands are present. Here, we report a case of subungual poroma in a 60-year-old man. The patient visited our consultation with a complaint of a 5-mm reddish nodule that developed below the nail plate of the left big toe 6 months ago. The mass had gradually increased in size and bled easily. Dermoscopy showed reddish-white globular-like structures, glomerular and hairpin vessels, and flower-like vessels surrounded by a whitish-pink network. Histopathological examination revealed a well-circumscribed lesion composed of collections of poroid cells connected to the epidermis and scattered luminal structures surrounded by cuticular cells. Although this was a rare case of a subungual tumor, the dermoscopic findings typical of poromas were confirmed through the preoperative removal of a portion of the nail from the lesion. Only nine cases, including ours, of subungual poromas have been reported in Japan and abroad; all seven toenail cases involved the big toe. Therefore, we considered the possibility that the onset of subungual poroma might be associated with mechanical stress. In addition, we focused on the plantar area of the foot, which is particularly loaded during walking and exposed to a large amount of mechanical stress. Furthermore, we examined the associations between the sites of plantar poroma and loading. The results showed that poromas most frequently occurred on the heel, which is the most loaded area, and not in the arch area. These findings suggest that mechanical stress might be a trigger for the occurrence of poromas.