Acantholytic dyskeratotic acanthoma: A rare and underappreciated entity

Question

What is your Diagnosis?

Answer

Diagnosis: Acantholytic dyskeratotic acanthoma

Discussion

Acanthoma is a benign tumor of epidermal keratinocytes, showing a broad range of histological patterns.¹ Acantholytic dyskeratotic acanthoma is a relatively uncommon variant of acanthoma, classified within the past decade. The term ‘focal acantholytic dyskeratosis’ was first used by Ackerman to describe incidental lesions showing acantholysis and dyskeratosis.² In contrast, genital lesions with similar characteristics had been described as ‘papular acantholytic dyskeratoma’ or ‘papular acantholytic dyskeratosis’.^3,4 However, non-genital lesions showing acantholysis and dyskeratosis were not adequately identified until Omulecki et al. defined acantholytic dyskeratotic acanthoma for the first time in 2007.¹ Acantholytic dyskeratotic acanthoma refers to a solitary, non-genital lesion with prominent acantholysis and dyskeratosis without cup-shaped architecture or follicular involvement.^4,6,7 However, whether it is an actual distinct diagnostic entity is debatable. There is no statement from the World Health Organization, and the description of acantholytic dyskeratotic acanthoma differs even within textbooks. Lever’s histopathology and McKee’s pathology textbooks describe acantholytic dyskeratotic acanthoma as a phenomenon rather than a separate entity,^8,9 while Weedon’s textbook considers acantholytic dyskeratotic acanthoma a separate entity.¹⁰

About 43 cases of acantholytic dyskeratotic acanthoma have been reported in the English literature to date [Table 1]. Patient ages ranged from 12 to 97 years, with 38 (88.4%) older than 40 years. The patients were often clinically suspected of having basal cell carcinoma, squamous cell carcinoma, and/or actinic keratosis. Most lesions were located on the trunk and often presented as a small papule of <1 cm. Among the 43 reported cases, three were in subungual areas,^13–15 three occurred in a transplant setting^5,12,13 and one after vemurafenib treatment.¹⁴ Among the three patients with a history of transplants, two presented with multiple lesions. However, the association between immunosuppression and acantholytic dyskeratotic acanthoma remains inconclusive.

Pathogenesis of acantholytic dyskeratotic acanthoma is still elusive. However, genetic and immunological factors along with viral infections, physical stimuli, and sunlight exposure, might play a role.^3,10 Histopathologically, acantholytic dyskeratotic acanthoma is characterised by acantholysis and dyskeratosis.^3,6 Therefore, it should be differentiated from other acantholytic disorders such as keratosis follicularis (Darier’s disease), transient acantholytic dermatosis (Grover’s disease), Hailey-Hailey disease, and warty dyskeratoma. As Darier’s, Grover’s and Hailey-Hailey’s diseases show distinct clinical features and immunofluorescence findings, they could be easily differentiated from acantholytic dyskeratotic acanthoma.⁹ On the contrary, it could be challenging to distinguish acantholytic dyskeratotic acanthoma from warty dyskeratoma as they share many histological features. However, unlike acantholytic dyskeratotic acanthoma, warty dyskeratoma is associated with a cup-shaped invagination or follicular involvement.^1,3,4,6,11 Last, acantholytic dyskeratotic acanthoma can also be easily differentiated from acantholytic acnathoma by the presence of prominent dyskeratosis.

Clinically, patients with acantholytic dyskeratotic acanthoma typically present with an asymptomatic solitary keratotic papule or plaque showing predilection to the trunk,^4,5 and resemble non-melanotic skin cancers such as squamous cell carcinoma, basal cell carcinoma or actinic keratosis.^4,5 However, acantholytic dyskeratotic acanthoma is a benign disease that can be easily treated through excision. Therefore, it is necessary to rule out acantholytic dyskeratotic acanthoma from other conditions to avoid unnecessary procedures and treatments. It can be relatively easily differentiated from other non-melanotic skin cancers histopathologically as it lacks cellular atypia and specific morphological features of those conditions.^1,3

Our case reinforces the necessity of classifying acantholytic dyskeratotic acanthoma as a distinct clinical entity. Examining and ruling out acantholytic dyskeratotic acanthoma as a clinical entity will assist in avoiding unnecessary or invasive procedures and treatments associated with another malignant disease with similar characteristics.