Intraepidermal proliferation of Merkel cells within a seborrheic keratosis: Merkel cell carcinoma in-situ or Merkel cell hyperplasia?

Abstract

Intradepidermal proliferation of Merkel cells without any dermal component has been interpreted as either a hyperplastic process secondary to chronic ultraviolet radiation (UVR) or a neoplastic process, namely, Merkel cell carcinoma (MCC) in-situ. The recent criteria that have been proffered to diagnose MCC in-situ, unfortunately, are identical to those that have been applied to Merkel cell hyperplasia in the past, posing a diagnostic quandary when faced with an intraepidermal proliferation of Merkel cells. Most previously reported cases of MCC in-situ have occurred within associated epithelial lesion that includes solar (actinic) keratosis and squamous-cell carcinoma in-situ. Similarly, Merkel cell hyperplasia has been reported to occur in association with a variety of epithelial lesions as well as on chronically sun-damaged skin. Herein, a case of an intraepidermal proliferation of Merkel cells within a seborrheic keratosis is presented accompanied by a discussion on whether the proliferation represents another case of Merkel-cell carcinoma in-situ or an incidental hyperplastic process on chronically sun-damaged skin.

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