Pedunculated clear cell acanthoma. Report of a case with dermoscopic observation

ARTICLE

Auteur(s) : Takamitsu Tanaka, Takako Arai, Takeko Ishikawa, Takamitsu Ohnishi, Shinichi Watanabe

Department of Dermatology, Teikyo University School of Medicine, 11-1, Kaga, 2-chome, Itabashi-ku, Tokyo 173-8605, Japan

Clear cell acanthoma is a distinct clinical and histological entity that was first described in 1962 by Degos et al. The clinical appearance is usually characterized by a nodule or plaque with thin scaly-crusts on the legs, although considerable variety exists. Silhouette of pedunculation is rare. Histologically, it has distinct features, with well-demarcated acanthosis consisting of clear cells. On the other hand, some authors reported dermoscopic findings consisting of dotted vessels or capillaries in reticular or net like patterns [1-5]. We describe a pedunculated clear cell acanthoma, and compare its dermoscopic findings with previous reports.

An 85-year-old Japanese female presented a skin lesion on a traumatic scar on her right lower leg. A small nodule had appeared about 10 years previously, and had gradually enlarged and elevated, asymptomatically. Physical examination revealed a red, elastic-soft, pedunculated round nodule, measuring 15 × 15 × 6 mm, on the anterior surface of her lower leg. The surface of the nodule was covered by waxy keratinous materials (figure 1A). No regional lymph node was palpable. Using a dermoscope, bunch-like, partly linear vessels on a pinkish-blotched background were observed translucently through the surface hyperkeratotic scales (figure 1B). Complete removal revealed that the present case consisted of irregular and partly pseudocarcinomatous acanthosis and edematous stroma forming a symmetrical pedunculated silhouette (figure 1C). The acanthosis was composed of clear cells, which had strikingly bright cytoplasms and normal nuclei. The rete ridges were elongated, and their margin consisted of normal basal keratinocytes. The surface showed parakeratosis, with few or no granular layers (figure 1D). There was neither dyskeratosis nor granular degeneration, although some areas showed acantholysis. Clear cells showed pallor and were stained strongly positive with periodic acid-Schiff (PAS). This reaction is diastase-labile, indicating the presence of glycogen.

Clear cell acanthoma was first described by Degos as a benign skin tumor originating from the epidermis. However, there has been controversy as to whether clear cell acanthoma is a tumor or a non-specific reactive dermatosis. On the basis of the histological features, its reactive and inflammatory nature have been commented upon. Some authors proposed that it is a localized form of inflammatory psoriasiform dermatoses, from the co-existence of both diseases. On the basis of the analysis of the keratin profile in clear cell acanthoma, expression of hyperproliferative markers also supported this notion. The fact that the present lesion is situated on a trauma scar is compatible with the inflammatory process hypothesis. However, the pedunculated silhouette suggests a tumoral nature, although a pedunculated appearance is a rare event in clear cell acanthomas. There have only been 4 reports of the variant in the literature [6].

There are few reports observing clear cell acanthoma by dermoscopy, and none observing pedunculated variants. In 2001, Blum et al. [1] first reported that dermoscopic examination revealed evenly distributed, partly linear, pinpoint-like capillaries in clear cell acanthoma. These capillaries are thought to correspond to dilated capillaries in elongated dermal papillae, as observed in psoriasis. Some authors also reported that clear cell acanthoma showed dotted vessels or capillaries in reticular or net-like patterns [2-5]. Furthermore, Zalaudek et al. [3] pointed out a slight difference in dermoscopic findings between clear cell acanthoma and psoriasis. Namely, pinpoint or dotted vessels did not display any homogenous distribution throughout the entire lesion of clear cell acanthoma, as they did in psoriasis. The present case indicated bunch-like, partly linear, vessels, which were more irregular than ordinary clear cell acanthoma and psoriasis. This peculiar finding is speculated to depend upon the large pedunculated nodule, which consisted of irregular or pseudocarcinomatous acanthosis and elongated dermal papillae.

Acknowledgements

References

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