Clear cell acanthoma
Degos acanthoma · clear cell acanthoma of Degos · pale cell acanthoma · acanthome à cellules claires
Clear cell acanthoma is a rare benign epithelial lesion, usually presenting in middle-aged or older adults as a slow-growing, solitary, red-brown, shiny or scaly papule/plaque on the lower leg. It is clinically non-specific and often needs biopsy, but dermoscopy can be highly suggestive when dotted vessels are arranged in linear or serpiginous strings, the classic “string of pearls” pattern. Its skin-oncology relevance is as a mimic of Bowen disease, BCC, pyogenic granuloma, eccrine poroma, clear-cell hidradenoma and amelanotic melanoma.
Clinical features
- Usually solitary; multiple lesions are reported but uncommon.
- Most often on the lower leg of a middle-aged or older adult.
- Slightly elevated to dome-shaped papule, plaque or nodule, commonly pink-red to brown, shiny or moist.
- Typical size is a few millimetres to around 2 cm.
- A wafer-like peripheral collarette of scale may be present; removing scale may reveal a moist or bleeding surface.
- Growth is slow and lesions may persist for years without complication.
Dermoscopy
- Most useful clue: pinpoint/dotted vessels arranged in linear, serpiginous or reticular strings, often described as a “string of pearls”.
- Additional reported features include a pale pink background, collarette scale, shiny white lines, glomerular vessels, haemorrhagic areas or orange crust.
- The pattern is helpful but not absolutely pathognomonic; a string-of-pearls-like arrangement can rarely be seen in other epidermal lesions.
- If the lesion is atypical, changing, ulcerated or clinically concerning, histology should override pattern recognition.
Histology
- Sharply circumscribed psoriasiform epidermal acanthosis.
- Keratinocytes have pale/clear glycogen-rich cytoplasm; PAS positivity is diastase-sensitive.
- Neutrophilic exocytosis and parakeratosis are common.
- Vessels in elongated dermal papillae explain the dotted-vessel dermoscopic pattern.
- Histology helps separate it from Bowen disease, poroma, hidradenoma and amelanotic melanoma.
Differential diagnosis
- Bowen disease / SCC in situ.
- Superficial or nodular BCC.
- Pyogenic granuloma or other friable vascular lesion.
- Inflamed seborrhoeic keratosis, dermatofibroma, actinic keratosis or verruca vulgaris.
- Eccrine poroma and clear-cell hidradenoma.
- Amelanotic melanoma, especially if rapidly growing, ulcerated or atypically vascular.
Management
- Diagnostic biopsy or complete excision is appropriate when the diagnosis is not secure clinically and dermoscopically.
- Small lesions are usually treated with shave excision, curettage or elliptical excision depending on site and diagnostic confidence.
- Once fully removed, recurrence is uncommon.
- No routine follow-up is needed for a completely removed, histologically confirmed clear cell acanthoma unless clinical uncertainty remains.
References
- DermNet. Clear cell acanthoma.
- Dermoscopy IDS/Dermoscopedia. Clear cell acanthoma.
- Lyons G et al. Dermoscopic features of clear cell acanthoma: five new cases and a review of existing published cases. Australas J Dermatol. 2015;56:206-211.
- Tiodorovic-Zivkovic D et al. Dermoscopy of clear cell acanthoma. J Am Acad Dermatol. 2015;72:S47-S49.
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