A 71–year-old Caucasian male presented to the dermatology clinic with a growth on his right lower leg that had been present for several months. The growth was slightly tender and occasionally bled following minor trauma. He denied any personal or family history of skin cancer. Examination revealed a 1-cm by 0.9-cm friable exophytic, erythematous plaque localized to the right distal leg. Dermatoscopic examination was performed and is shown at left.
What is Your Diagnosis?
DIAGNOSIS: Clear Cell Acanthoma
A clear cell acanthoma (CCA), also referred to as “pale cell acanthoma” or “Degos’ acanthoma,” was first described by Degos et al1 in 1962 as a benign epidermal tumor. CCA is clinically recognized as a pink-to-brown, well-demarcated glistening or moist dome-shaped nodule or plaque that is asymptomatic.1,2,3 Lesions are often slow-growing and typically range from a few millimeters to several centimeters in diameter.2 A collarette of thin, wafer-like scale may be found at the periphery.4 CCA most frequently occurs as a solitary lesion on the leg and less commonly on the trunk, face, upper extremities and scalp.4 Multiple lesions and disseminated forms have rarely been reported.5
Examination of CCA by dermato-scopy demonstrates a psoriasiform pattern with a squamous surface, translucid collarette and dotted vessels.3 These vessels represent dilated capillary loops and are typically arranged in a reticular or string-like fashion, which is specific to CCA.3,6
CCA may appear clinically similar to a variety of benign and malignant neoplasms including basal cell carcinoma, squamous cell carcinoma, Bowen’s disease, amelanotic melanoma and actinic keratosis. Other cutaneous conditions that may mimic CCA include hemangioma, dermatofibroma, verruca vulgaris, psoriasis, pyogenic granuloma and irritated seborrheic keratosis.
Clear cell acanthoma is a relatively rare entity and has no known systemic or genetic associations.4 A recent study by Morrison et al4 reviewed one private regional dermatopathology laboratory’s biopsy results over a period of 10 years and found an incidence of 0.03% (411 cases among 1,489,818 biopsies) for CCA. CCA most commonly presents after age 40 and affects males and females equally.7
In CCA, the epidermis may demonstrate parakeratosis, scale with collections of neutrophils and acanthosis; crust may or may not appear.3,8 A key feature of CCA is a sharp demarcation from adjacent normal keratinocytes by its pale-staining, glycogen-filled keratinocytes.3,4,8,9 These keratinocytes are periodic, acid-Schiff positive and diastase sensitive.8 Other findings include elongation of rete ridges, thinning of suprapapillary plates and dilation and tortuosity of the capillaries located in the papillary dermis.3,4,9
Surgical excision or cryotherapy is often curative and CCA usually does not recur. Spontaneous involution has also been reported.
Dr. Kim is a clinical research fellow in dermatology at Duke University Medical Center in Durham, NC. Dr. Lichon is a third-year resident at Loyola University Medical Center in Maywood, IL. Dr. Mehta is the Director of Mohs Micrographic Surgery at Rush University in Chicago, IL.