Dermoscopic features of clear cell acanthoma: five new cases and a review of existing published cases

Clear Cell Acanthoma: A Series of 70 Cases

BACKGROUND AND OBJECTIVE

Clear cell acanthoma (CCA) is an uncommon lesion histologically characterized by the presence of epidermal acanthosis with keratinocytes containing clear cytoplasm. Although many single cases of CCA have been described, few case series have been published. The aim of this study was to describe the clinical characteristics of CCA in our practice setting.

MATERIAL AND METHODS

Retrospective study of patients diagnosed with CCA at Hospital Universitario de Bellvitge in Barcelona, Spain, between 1995 and 2021. We conducted a chart review to record age, sex, number and location of lesions, diameter, time since onset, clinical characteristics, suspected clinical diagnosis, and treatment.

RESULTS

Seventy patients (30 women and 40 men) with a mean (SD) age of 62 (13) years were diagnosed with CCA during the study period. Median (interquartile range) time since onset was 2 (4) years and median lesion diameter was 6 (5) mm. One woman had multiple lesions. Lesions were located on the lower extremities in 57 patients (81%), the posterior aspect of the trunk in 8 (11%), the anterior aspect of the trunk in 4 (5%), and the upper extremities in 1 (1%). CCA was clinically suspected in 40% of patients seen by dermatologists.

CONCLUSIONS

CCA presents as an erythematous, dome-shaped lesion with pinpoint vessels and an epidermal collarette. The accuracy of clinical diagnosis has improved relative to earlier series, possibly due to a better clinical understanding of this lesion and a greater use of dermoscopy.

[Translated article] Clear Cell Acanthoma: A Series of 70 Cases

BACKGROUND AND OBJECTIVE

Clear cell acanthoma (CCA) is an uncommon lesion histologically characterized by the presence of epidermal acanthosis with keratinocytes containing clear cytoplasm. Although many single cases of CCA have been described, few case series have been published. The aim of this study was to describe the clinical characteristics of CCA in our practice setting.

MATERIAL AND METHODS

Retrospective study of patients diagnosed with CCA at Hospital Universitario de Bellvitge in Barcelona, Spain, between 1995 and 2021. We conducted a chart review to record age, sex, number and location of lesions, diameter, time since onset, clinical characteristics, suspected clinical diagnosis, and treatment.

RESULTS

Seventy patients (30 women and 40 men) with a mean (SD) age of 62 (13) years were diagnosed with CCA during the study period. Median (interquartile range) time since onset was 2 (4) years and median lesion diameter was 6 (5)mm. One woman had multiple lesions. Lesions were located on the lower extremities in 57 patients (81%), the posterior aspect of the trunk in 8 (11%), the anterior aspect of the trunk in 4 (5%), and the upper extremities in 1 (1%). CCA was clinically suspected in 40% of patients seen by dermatologists.

CONCLUSIONS

CCA presents as an erythematous, dome-shaped lesion with pinpoint vessels and an epidermal collarette. The accuracy of clinical diagnosis has improved relative to earlier series, possibly due to a better clinical understanding of this lesion and a greater use of dermoscopy.

Clear cell acanthoma

Clear cell acanthoma is a rarely diagnosed tumor with variable clinical morphology that is usually only recognized by its histopathological features. The primary lesion is a red papule a few millimeters in diameter that often occurs as a single lesion on the lower extremities. In dermoscopy, resemblance of the vessels to a string of pearls is a largely specific finding of clear cell acanthoma. In contrast to the initially uncharacteristic clinical findings, histopathology of clear cell acanthomas is characterized by a typical compact, well-demarcated acanthosis consisting of pale-staining, PAS-reactive keratinocytes. As etiology and pathogenesis are both unclear, nosology of clear cell acanthoma is also controversial, with an ongoing debate as to its classification as cutaneous neoplasia or reactive inflammatory dermatosis.

Differences in dermoscopic findings between early and mature clear cell acanthoma

Clear cell acanthoma (CCA) is a rare benign epidermal tumor that is difficult to diagnose by visual inspection. Conversely, its diagnosis by dermoscopy is relatively easy owing to the characteristic serpiginous arrangement of coiled vessels, sometimes described as the "string-of-pearls" formation. However, in few published reports, the dermoscopic diagnosis of mature CCA has been reported. Here, we report the histopathological and detailed dermoscopic findings of two CCA cases. Between these, one case was of early (~6 months) CCA exhibiting the characteristic vascular string-of-pearls formation, whereas the other was of a more mature (~10 years) CCA; although the latter case showed combined thick and thin white intersecting lines with large coiled vessels and/or red clods, it had the string-of-pearls formation. Thus, regardless of CCA maturity, the string-of-pearls formation was present. We propose that the combination of combined thick and thin white intersecting lines along with the vascular string-of-pearls formation reflecting large coiled vessels and/or red clods on dermoscopy is a diagnostic clue to mature CCA.

Dermoscopic features of clear cell acanthoma

Clear cell acanthoma is an uncommon type of benign epithelial tumor. Typically, it is a solitary lesion found on the lower limbs. It presents as a nodule or small plaque with slow and well-defined growth. Diagnosis used to be clinical and histopathological, but the advent of dermoscopy has led to an increase in diagnostic accuracy. We describe a case in which dermoscopy proved highly useful for diagnosis of the lesion.

Multiple clear cell acanthomas and a sebaceous lymphadenoma presenting in a patient with Cowden syndrome - a case report

Cowden syndrome (CS) is an uncommon autosomal dominant multiorgan/system genodermatosis. It is characterized by the development of multiple hamartomas of endodermal, mesodermal and ectodermal origin, an increased lifetime risk of breast, thyroid, endometrial and other cancers and an identifiable germline mutation. Mucocutaneous hamartomas are the most common lesions seen and mainly include facial trichilemmomas, oral mucosal papillomas and benign acral keratoses. Herein, we report a case of a 63-year-old Caucasian male with a long-established diagnosis of CS and history of thyroid cancer, colonic polyps, and innumerable trichilemmomas, seborrheic keratoses, squamous papillomas and non-melanoma skin cancers excised in the past. He presented in four separate occasions with small skin-colored papulonodular lesions that upon excision revealed to be clear cell acanthomas. He also developed a tumor in the preauricular area that was completely resected and was found to be a sebaceous lymphadenoma (SLA) of the parotid gland. This is to our knowledge, the second report of clear cell acanthoma and also the second reported case of SLA in a patient with CS.

Malignant Clear Cell Acanthoma: Report of a Rare Case of Clear Cell Acanthoma-Like Tumor With Malignant Features

An erythematous and moist tumor nodule on the left temple of a 92-year-old woman was biopsied and identified as a clear cell acanthoma (CCA)-like tumor with malignant cytology and high proliferation activity. This case is similar to 2 cases reported previously as atypical CCA. The authors believe that these tumors are malignant counterparts of CCA and propose to call them malignant CCA. The clinicopathologic features of the present case are described along with dermoscopic findings.