Subungual clear cell acanthoma

A 70-year-old man presented with a painless papule on the nail bed of his right third finger, which had been present for 2 years. The patient did not have a history of nail trauma, nor did he have psoriasis or other inflammatory dermatosis. On physical examination there was a 4 4 mm erythematous to yellowish subungual keratotic papule with longitudinal splitting of the nail plate and ulceration on the nail bed of the right third finger (Figure 1A). The lesion was tender and firm in texture. Dermoscopy showed keratotic papules with a few dotted vessels at the peripheral area. We partially removed the nail plate to create a wedge-shaped window (Figure 1B) and then excised the tumor. Histopathology showed parakeratosis, marked acanthotic lobules of clear epidermal cells with neutrophilic and lymphocytic exocytosis, and heavy infiltrates of lymphocytes and plasma cells in the dermis (Figure 2A and B). Abundant diastase liable glycogen was shown in the epidermal squamous cells by periodic acideSchiff staining, and a clear cell acanthoma (CCA) was confirmed (Figure 3A and B). As the histopathology showed no deep margin involvement, the patient did not receive further radiological examination. There was no recurrence in the following 6 months. The nail plate grew gradually with normal appearance. CCA is a benign tumor of epithelial origin andwas first described by Degos et al in 1962.1 CCA is a benign epidermal dermatosis which usually presents as a solitary lesion ranging in size from 5 mm to 20 mm; however, multiple and disseminated forms of CCA have also been reported. Wafer-like scales often surround the lesion in a collarette. CCA often occurs in middle-aged people without sex predominance. The largest evaluation of CCA showed that the leg is the most common location (51%), followed by the trunk and arms.2 Other rare locations include the umbilicus, hallus, and vermilion. However, subungual CCA has not yet been reported. In addition to CCA, a variety of malignant or benign lesions affect the subungual region, including squamous cell carcinoma, acral lentiginous melanoma, glomus tumors, onychomatricoma, neurofibroma, subungual exostosis, subungual wart, subungual keratoacanthoma, and pincer nail deformity.3 The diagnosis should be made by histopathological findings. Histopathologically, CCA is composed of well-demarcated acanthotic epidermis. The clear cells have abundant glycogen, which can be shown by positive periodic acideSchiff staining. Neutrophilic exocytosis and dilated vessels in the upper dermis