The histopathologic differential diagnosis of

The histopathologic differential diagnosis of desmoplastic cellular neurothekeoma includes melanocytic tumor (such as desmoplastic Spitz\'s nevus and desmoplastic melanoma), desmoplastic squamous carcinoma, cellular dermatofibroma, plexiform fibrohistiocytic tumor, benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma, and piloleiomyoma. They can be distinguished by clinical presentation, histological features, and immunohistochemical stains which are summarized in . Our case lacks the plexiform pattern, and its rare and sporadic weak immunohistochemical reaction for EMA is quite different from that of benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma. Soft tumors with the most similar histological and immunohistochemical findings are plexiform fibrohistiocytic tumors. This type of tumor usually locates in the deeper dermis or subcutis. Only if distinctive biphasic architecture, nodules of macrophages, and osteoclastic giant bet inhibitor surrounded by fascicles of fibroblastic spindle cells are present, are they helpful to distinguish them from desmoplastic cellular neurothekeoma. Plexiform fibrohistiocytic tumor has a reported local recurrence rate of 12–40% and rare regional or systemic metastases.
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 (A). 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 (B) 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 (A and B). Abundant diastase liable glycogen was shown in the epidermal squamous cells by periodic acid–Schiff staining, and a clear cell acanthoma (CCA) was confirmed (A 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 and was first described by Degos et al in 1962. 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. 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. 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 acid–Schiff staining. Neutrophilic exocytosis and dilated vessels in the upper dermis are also features. The pathogenesis of CCA is still to be ascertained. Some workers have suggested that CCA is a benign neoplasm. However, recent reports have shown that CCA develops on areas of pre-existing inflammatory dermatosis, such as stasis dermatitis, bacterial infection, psoriatic plaques, trauma, nipple eczema, and split-thickness skin graft. In one review of CCA, clinical and histopathological findings of chronic inflammation were found in 10 of 14 patients. Recent studies have therefore speculated that CCA is a reactive dermatosis. In the case reported here, heavy infiltrates of lymphocytes and plasma cells in the dermis indicated a previous inflammatory process. The histopathological findings support the hypothesis that CCA is a reactive dermatosis.