Are You Confident of the Diagnosis?
What you should be alert for in the history
Clear cell acanthomas often appear as a slowly growing papule or plaque on the lower extremities. These lesions are usually asymptomatic.
Characteristic features on physical examination
A clear cell acanthoma appears as a solitary, well defined, and moist pink-red nodule up to 2 cm in diameter. These lesions may have a collarette surrounding the border. Crusting and scale are common. These benign lesions are most commonly found on the lower extremeties, especially the shins.
Expected results of diagnostic studies
In histologic examination, an acanthotic epidermis is made up of large edematous cells with pale staining cytoplasm. There is a sharp demarcation between the tumor and adjacent normal epithelium. A characteristic finding is the presence of neutrophils within the epidermis to the level of the stratum corneum. The epidermal cells in this lesion have large amounts of glycogen and stain with Periodic Acid Schiff (Figure 1, Figure 2).
Eccrine poroma is an adnexal tumor that may simulate a clear cell acanthoma clinically, but occurs on acral skin. They are distinct histologically, with plump epithelial cells with focal ductal formation.
Clear cell hidradenoma may also appear clinically similar to a clear cell acanthoma, but occur most commonly on the head and neck. Histologically, these lesions consist of a dermal tumor with ductal differentiation, cyst degeneration, and clear cells.
Basal cell carcinoma is a malignant neoplasm that occurs on sun-damaged skin. Often it has a pink, translucent surface and a rolled edge. On histologic examination, this tumor is composed of basaloid islands protruding from the basal layer. Often these islands are separated from the surrounding connective tissue by mucin.
Squamous cell carcinoma is a malignant tumor that also occurs on sun-damaged skin. Clinically, it may appear identical to a clear cell acanthoma, but shows a proliferation of atypical squamous cells on histology.
Amelanotic melanoma may be clinically indistinguishable from a clear cell acanthoma. On histologic examination however, malignant melanocytes are present.
Who is at Risk for Developing this Disease?
Clear cell acanthomas most commonly occur during middle-age and have no ethnic or sexual predisposition. They are not associated with any other disease states.
What is the Cause of the Disease?
There is no known cause, predisposition, or precursor lesion for this benign epidermal tumor.
Systemic Implications and Complications
There are no other disease states associated with the development of a clear cell acanthoma.
-Electrodessication and curettage
-Carbon dioxide laser vaporization
Optimal Therapeutic Approach for this Disease
Simple surgical excision is the best method for removing a clear cell acanthoma. Simple saucerization with application of ointment such as vaseline and a bandage will allow healing of the site within 1-2 weeks. More importantly, this will allow histologic examination of the lesion to exclude malignant conditions.
Other destructive methods, including cryosurgery, laser, and electrodessication can also be employed if surgical excision cannot be employed. These methods also heal in 1-2 weeks, but may have a higher risk of developing a cosmetically unappealing scar.
If completely removed or destroyed, clear cell acanthomas should not recur. If a lesion does recur, it should be excised and submitted for histologic examination to exclude more serious tumors included in the differential diagnosis.
Unusual Clinical Scenarios to Consider in Patient Management
Occasionally these lesions may be pigmented. This may present the clinical appearance of an atypical or ulcerated pigmented lesion. Biopsy for histologic examination is essential in these lesions. It is also important to note that squamous cell carcinomas may occur within clear cell acanthomas. Hypertrophic, asymmetric or otherwise unusual lesion should be submitted in their entirety for histologic examination.
What is the Evidence?
Morrison , LK, Duffey , M, Janik , M, Shamma , HN. “Clear cell acanthoma: a rare clinical diagnosis prior to biopsy”. Int J Dermatol . vol. 49. 2010. pp. 1008-11. (This reference discusses the difficulty in making a clinical diagnosis of a clear cell acanthoma correctly. In many cases when clear cell carcinoma is submitted for histologic examination, the differential diagnosis fails to mention a clear cell acanthoma. This may be due to the relative rarity of clear cell acanthomas as well as the concern of physicians for more serious conditions that mimic clear cell acanthomas.)
Langer , K, Wuketich , S, Konrad , K. “Pigmented clear cell acanthoma”. Am J Dermatopathol . vol. 16. 1994. pp. 134-9. (This article presents five pigmented clear cell acanthomas. The histologic features of clear cell acanthoma are discussed, including the melanosome transfer inhibition from dendritic melanocytes within the epidermis of these examples. This leads to the retention of pigment within the melanosomes and clinical pigmentation of these lesions.)
Parsons , ME, Ratz , JL. “Squamous cell carcinoma in situ arising within clear cell acanthoma”. Dermatol Surg . vol. 23. 1997. pp. 487-8. (This reference presents an interesting case of a squamous cell carcinoma arising within a clear cell acanthoma.)
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