Background
In 1968, Bart et al [1] described 10 cases of an uncommon acquired growth that was located on the fingers. Although it clinically resembled a cutaneous horn or rudimentary supernumerary digit, it had distinct histopathological findings. The authors named this growth acquired digital fibrokeratoma (ADFK). Subsequently, Pinkus [2] reported 28 more cases; however, these lesions occurred not only on the fingers, but also on the proximal hand, toes, [3] sole, and one in the prepatellar region. For this reason, Verallo et al suggested the entity might more appropriately be called an acral fibrokeratoma. [4]
Similar growths have been reported to occur in the subungual or periungual region of patients with tuberous sclerosis, and they are referred to as Koenen tumors or garlic clove fibromas. They differ, however, in that they tend to be multilobulated and involve several digits and, histologically, may have atypical stellate myofibroblasts. [5]
Pathophysiology
Despite the fact that most patients deny a history of precedent trauma, the major hypothesis is that subclinical injury contributes to the development of acquired digital fibrokeratomas. [1] One case report describes an ADFK on the toe developing simultaneously with gingival overgrowth in a renal transplantation patient on cyclosporine, which the authors suggested may represent a causal association. [6]
Etiology
The etiology of acquired digital fibrokeratomas is unknown. Although trauma has been implicated, no studies can substantiate this hypothesis.
One report describes familial occurrence of an acral fibrokeratoma variant that had mucinous deposition; however, the case reported by Moulin et al [7] histologically more closely resembles a superficial acral fibromyxoma.
Epidemiology
Frequency
Currently, no means of tracking nonmelanoma skin cancer, much less various benign dermatological conditions, are available in the United States; therefore, the actual incidence of acquired acral fibrokeratoma is unknown. Most cases of acquired digital fibrokeratoma reported in the literature involve individual case reports presented because of the lesions' unusual size, location, histological features, or association with other conditions. Only a few reports of describe a series of patients, with 50 patients being the most reported from any one institution. [8] Therefore, whether acquired digital fibrokeratoma is rare or rarely reported remains unclear.
Race
Acquired digital fibrokeratomas have been reported in persons of all races.
Sex
Acquired digital fibrokeratomas seem to have a slight male predominance; however, at this time too few cases have been described to adequately assess the significance of any sexual predilection. [9] A case report from 2020 described an acquired digital fibrokeratoma on the heel of a pediatric female patient. [10]
Age
The patients reported with acquired digital fibrokeratomas range in age from 12-70 years, with most cases occurring in middle-aged adults. Clinically similar lesions that occur in young children are more likely to represent rudimentary supernumerary digits.
Prognosis
Acquired digital fibrokeratomas are benign stationary lesions that are more cosmetically bothersome than they are problematic. However, patients who have been reported to have giant acral digital fibromas on the dorsum or plantar surface [11, 12, 13] of the foot may report some discomfort. [12]
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Clinical picture of a pedunculated acquire digital fibrokeratoma.
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Flat-topped, skin-colored acquired digital fibrokeratoma in an acral location.
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Slightly raised skin encircling the base of an acquired digital fibrokeratoma, creating a moat.
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Domed-shaped papule with overlying hyperkeratosis. The dermal core is composed of increased collagen bundles and blood vessels oriented along the vertical axis of the lesion.
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Close up showing the increased collagen bundles and blood vessels oriented along the vertical axis of the lesion.
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A different acquired digital fibrokeratoma showing similar findings of a domed-shaped lesion with a vertically aligned fibrovascular core.
