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]
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.[7] 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.[8]
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[9, 10, 11] of the foot may report some discomfort.[10]
History
Most acquired digital fibrokeratoma patients present with an asymptomatic protuberance.
Physical Examination
Clinically, acquired digital fibrokeratomas manifest as solitary, skin-colored, dome-shaped papules or tall fingerlike protrusions with a hyperkeratotic surface. Most acquired digital fibrokeratoma lesions are small and do not exceed 1.5 cm in height or diameter, but giant lesions measuring in excess of 3 cm have been documented.[12, 13]
An important clinical finding reported to help differentiate acquired digital fibrokeratomas from other similar lesions is a collarette of slightly raised skin that encircles the base of the lesion, thereby creating a moatlike configuration.[14]
View Image | Clinical picture of a pedunculated acquire digital fibrokeratoma. |
View Image | Flat-topped, skin-colored acquired digital fibrokeratoma in an acral location. |
View Image | Slightly raised skin encircling the base of an acquired digital fibrokeratoma, creating a moat. |
Causes
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[15] histologically more closely resembles a superficial acral fibromyxoma.
Other Tests
To date, dermoscopic findings have only been reported in two cases. One report describes a homogeneous light-yellowish core with a white scaly collar reflective of epidermal acanthosis, hyperkeratosis, and dense collagen fibers, which was seen histologically. In addition, the authors also describe red spherical vessels surrounding the entire lesion. The other report revealed the presence of numerous clumps of homogenous red lacunae divided by a white meshwork-like septal wall, along with telangiectasia in the adjacent skin. The latter authors attributed the white mesh-like network to the marked hyperkeratosis overlying irregular elongated rete ridges seen on histological examination.[20]
Histologic Findings
The overall architecture of an acquired digital fibrokeratoma is a small, well-circumscribed, dome-shaped or narrow elongated papule. The stratum corneum is typically hyperkeratotic, which tends to be most pronounced toward the summit of the lesion. The epidermis can be acanthotic, with elongation of the rete ridges or can be slightly attenuated.
The dermal core of an acquired digital fibrokeratoma displays one of three histological patterns, which were originally described by Bart et al[1] and further characterized by Kint et al.[21] Type I acquired digital fibrokeratoma is the most common type and consists of a dermal core composed of thick, closely intertwined collagen bundles that are often oriented along the vertical axis of the lesion. Between the collagen bundles are numerous capillaries, varying numbers of fibroblasts, and thin elastic fibers. Type II lesions are less common, and histologically resemble type I lesions, but in addition have a significantly increased number of fibroblasts arranged in fascicles and markedly reduced numbers of elastic fibers. Type III acquired digital fibrokeratoma is the least common type and consists of a dermal core that is poorly cellular and edematous with a reduced number of elastic fibers.
View Image | Domed-shaped papule with overlying hyperkeratosis. The dermal core is composed of increased collagen bundles and blood vessels oriented along the vert.... |
View Image | Close up showing the increased collagen bundles and blood vessels oriented along the vertical axis of the lesion. |
View Image | A different acquired digital fibrokeratoma showing similar findings of a domed-shaped lesion with a vertically aligned fibrovascular core. |
Surgical Care
Simple excision of acquired digital fibrokeratomas is curative; recurrence is rare.
Author
Elizabeth K Satter, MD, MPH, Dermatologist and Dermatopathologist
Disclosure: Nothing to disclose.
Specialty Editors
David F Butler, MD, Former Section Chief of Dermatology, Central Texas Veterans Healthcare System; Professor of Dermatology, Texas A&M University College of Medicine; Founding Chair, Department of Dermatology, Scott and White Clinic
Disclosure: Nothing to disclose.
Christen M Mowad, MD, Professor, Department of Dermatology, Geisinger Medical Center
Disclosure: Nothing to disclose.
Chief Editor
William D James, MD, Paul R Gross Professor of Dermatology, Vice-Chairman, Residency Program Director, Department of Dermatology, University of Pennsylvania School of Medicine
Disclosure: Received income in an amount equal to or greater than $250 from: Elsevier; WebMD.
Additional Contributors
Abby S Van Voorhees, MD, Assistant Professor, Director of Psoriasis Services and Phototherapy Units, Department of Dermatology, University of Pennsylvania School of Medicine, Hospital of the University of Pennsylvania
Disclosure: Received honoraria from Amgen for consulting; Received honoraria from Abbott for consulting; Partner received salary from Merck for management position; Received honoraria from Abbott for speaking and teaching; Received honoraria from Amgen for review panel membership; Received honoraria from Centocor for consulting; Received honoraria from Leo for consulting; Received none from Merck for other.
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