Onycholemmal variant of keratoacanthoma centrifugum marginatum as an expression of mutated committed stem cells in a conceptual pathway

We describe a 43-year-old woman with a 10-year history of grossly hyperkeratotic nodules which progressively extended over the right ring finger. These involuted leaving pale, atrophic skin in their wake. At presentation, the advancing border had an arciform series of nodules in the pattern of keratoacanthoma centrifugum marginatum. The presence of filiform keratinisation that encased the nail plate, gross onychogryphotic masses of keratin on the ventral finger surface and a flat nail-like plate of keratin on the dorsal finger surface were distinctive features. Skin biopsy showed epidermal acanthosis, gross papillomatous cutaneous horn formation that had onycholemmal features. The pathology differed from keratoacanthoma and was not crateriform or infundibulocystic. Although HPV was not detected on immunohistochemistry, pathogenesis may still represent an HPV-related transfection of onycholemmal keratin committed stem cells producing an onycholemmal variant of keratoacanthoma centrifugum marginatum. A conceptual model linked to advances in follicular stem cell biology is formulated to explore this case.