Answer of Dermatopathology Case 25

Clear Cell Acanthoma

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Abstract:

Comparing in vivo reflectance confocal microscopy, dermoscopy, and histology ofclear-cell acanthoma. Dermatol Surg. 2009 Jun;35(6):952-9.

BACKGROUND: Clear cell acanthoma (CCA) is a rare, benign neoplasm of unknown etiology, whose dermoscopic and histological features have been previously described. Usually, CCA can be diagnosed by clinical and dermoscopic examination. In some cases, diagnosis remains uncertain, and histological examination is needed. The aim of this paper was to describe the features of reflectance confocal microscopy (RCM) in diagnosing CCA, compare them with findings on dermoscopy and histology, and evaluate their possible usefulness in CCA evaluation. PATIENTS AND METHODS: Five lesions diagnosed clinically as CCA were imaged using dermoscopy and RCM. All lesions were surgically excised to confirm the diagnosis and compare the morphological attributes under light microscopy with in vivo imaging. RESULTS: RCM showed well-circumscribed lesions, often edged by a hyperkeratotic collarette with parakeratosis ; inflammatory cells in thespinous layer ; large keratinocytes ; acanthosis with papillomatosis ; epidermal disarray ; and dilated capillaries forming glomeruloid shapes in the upper dermis. CONCLUSIONS: In this small study, RCM was able to identify most of the established diagnostic histological features of CCA. RCM appears to be a useful tool for in vivo diagnosis of CCA and may help avoid unnecessary biopsies.

Clear-cell acanthoma versus acanthosis: a psoriasiform reaction pattern lacking tricholemmal differentiation. Am J Dermatopathol. 2007 Aug;29(4):378-84.

Clear-cell acanthoma (CCA) has been reported to be a benign epidermal neoplasm; however, several authors have suggested alternative differentiation as well asother nosologic categories, including a reactive dermatosis. Fourteen CCAs, ten tricholemmomas, and seven cases of psoriasis were reviewed with conventional microscopy, periodic acid-Schiff stains, and immunohistochemical stains. Twelve of fourteen (86%) CCAs were associated with underlying or adjacent conditions.The CCAs stained immunohistochemically in a pattern similar to normal epidermis and psoriasis. Tricholemmomas stained in a distinctly different pattern with MNF116 and NGFR/p75. These cases demonstrate CCA in settings that reflect chronic inflammation, primarily scars and stasis dermatitis, and with an immunophenotype that parallels psoriasis. These findings support the contention that CCA does not show outer follicular sheath (tricholemmal) differentiation. Furthermore, these cases lend additional support to the contention that CCA represents a psoriasiform reaction pattern, which, in appropriately taken biopsies, usuallyhas a demonstrable associated condition . Nonetheless, the precise nosology of this phenomenon has yet to be elucidated completely.