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Clear Cell Acanthoma - Submitted on: Monday December, 23, 2002
Contributed by:Aaron Caplan, MD
Clear cell acanthoma is a distinct clinical and histological entity that was first described in 1962 by Degos, et al.(1) Since then, multiple authors have further characterized the clinical and histologic features of this uncommon, but hardly rare, lesion. Although originally considered to be a benign neoplasm of the epidermis, some authors now believe that this lesion may actually represent a peculiar reactive dermatosis.(9)

Definition:
Clear cell acanthoma is a benign, slow growing nodular or plaque-like hyperplasia of the epidermis characterized clinically by a predilection for the lower extremities of the middle aged and elderly, and histologically by a sharply demarcated intra-epidermal proliferation of glycogen-rich keratinocytes.

Clinical Features:
Clear cell acanthoma generally presents as a firm, brown-red, well-demarcated nodule or plaque on the lower extremities of middle-aged to elderly individuals (7). It has, however, been reported in younger patients and rarely at sites other than the legs, including the abdomen where it was first described by Degos (3). It is usually solitary, although patients with multiple lesions have been reported (5). The lesion generally ranges in size from 5 mm to 2 cm, has a “wafer-like” scaly collarette at the periphery (4), and vascular puncta on the surface (4). It has been described by some as having a “stuck on” appearance, much like a seborrheic keratosis (3,4), and/or the appearance of a vascular lesion like a pyogenic granuloma (4,6). The lesion is characterized by slow growth, and may persist for years (2,3). Spontaneous involution has been reported (7). Its dermatoscopic appearance is similar to that of psoriasis vulgaris (8). The clinical differential diagnosis includes: dermatofibroma, inflamed seborrheic keratosis, pyogenic granuloma, basal cell carcinoma, squamous cell carcinom, verruca vulgaris, psoriatic plaque, and even melanoma.

Histology:
Figures
(Click on an image for a larger view)
Low power view of clear cell acanthoma
Corneal microabcesses
Sharp lateral demarkation
Sparing of adnexal structures
Histologically, clear cell acanthoma is characterized by a sharply demarcated psoriasiform epidermal hyperplasia composed of a proliferation of slightly enlarged keratinocytes with pale-staining cytoplasm (6). Although the basal cells at the base of these lesions are typically less clear, they lack melanin much like the proliferating clear keratinocytes (3,6). The intraepidermal adnexal structures are spared from the clear cell changes (6). Mild spongiosis is usually present along with scattered exocytosis of neutrophils and neutrophil debris (3). The neutrophils may form small intraepidermal microabscesses (3). A parakeratotic scale is generally present with occasional pustulation along with focal thinning of the suprapapillary plate (7). Atypia is rarely encountered in clear cell acanthomas (7). Characteristic histologic changes are also found in the dermis with edematous dermal papillae, containing increased vascularity and a mixed inflammatory infiltrate including lymphocytes, plasma cells and neutrophils (7). Occasional sweat duct dilatation and hyperplasia is also encountered (6). Staining with PAS with and without diastase demonstrates the presence of glycogen within the cytoplasm of the proliferating cells. Fittingly, these cells have also been shown to lack phosphorylase, an enzyme necessary for the degradation of glycogen (3,6).


Treatment:
Simple surgical excision is curative.

Bibliography:
  • Degos R, Delort J, Civatte J, Poiares BA: Tumeur epidermique d’aspect particulier: acanthome a cellules claires. Dermatologica 129:361-71, 1962.
  • Zak FG, Martinez M, Statsinger AL: Pale cell acanthoma. Arch Derm 93:674-8, 1966
  • Jones EW, Wells GC: Degos’ acanthoma (acanthome a cellules claires): a clinical and histological report of nine cases. Arch Derm 94:286-94, 1966.
  • Fine RM, Chernosky ME: Clinical recognition of clear-cell acanthoma (Degos’). Arch Derm 100:559-62, 1969.
  • Trau H, Fisher BK, Schewach-Millet M: Multiple clear cell acanthomas. Arch Derm 116:433-4, 1980.
  • Elder D, Elensitas R, Jaworsky C, et al., in: Lever’s Histopathology of the Skin, 8th Edition. Philadelphia, Lippincott-Raven, 1997, pp.693-4.
  • Weedon D, Strutton G, in: Skin Pathology. Edinburgh, Churchill Livingstone, 1997, pp.641-2
  • Blum A, Metzler G, Bauer J, et al.: The dermatoscopic pattern of clear cell acanthoma resembles psoriasis vulgaris. Dermatology 203:50-2, 2001
  • Finch TM, Tan CY: Clear cell acanthoma developing on a psoriatic plaque: further evidence of an inflammatory aetiology?. Br J Dermatol 142:842-4, 2000.
     

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