CASE #2: Acquired digital fibrokeratomas

Acquired digital fibrokeratomas (ADFKs) are uncommon skin neoplasms that manifest as asymptomatic, solitary, smooth, dome-shaped, flesh-colored papules or nodules, usually with a collarette at the base creating a moatlike configuration at their bottom.

These growths are usually solitary, but multiple lesions have rarely been reported. Most ADFKs measure 0.5 to 1.5 cm in height or diameter, but larger growths with a diameter or height greater than 3 cm have been noted. ADFKs develop most commonly on the fingers and toes. A number of cases have been noted on the heel. A few patients with ADFKs occurring on the elbow, wrist, calf, and the prepatellar area have been seen.

The epidemiology of ADFKs is not well defined. ADFKs are most common in men, but the paucity of reports makes a true sexual predilection difficult to establish. ADFKs most commonly arise in middle age, with reported ages of onset ranging from 12 to 70 years (average age 40 years). No racial predilection has been noted.

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Investigators first described ADFKs in 1968 in a series of 10 patients with hand lesions.14 Later that year, investigators noted 28 cases of similar lesions, with some occurring on the arms and legs and suggested that “acquired acral fibrokeratoma” would be a more accurate description.15

The differential diagnosis of ADFKs includes: corn, superficial acral fibromyxoma, aggressive digital papillary adenocarcinoma, squamous cell carcinoma (in particular, subungual keratoacanthoma), osteoma, cutaneous horn, verruca vulgaris, supernumerary digit, Koenen’s tumor (periungual fibromas), pyogenic granuloma (lobular capillary hemangioma), acrochordon, infantile digital fibromatosis, and neurofibroma.

Papules or nodules that arise before puberty and fit the description of ADFKs are most likely supernumerary digits. Supernumerary digits occur on the proximal portion of the fifth digit and are made up of abundant nerve bundles. Unlike an ADFK, an acquired periungual fibrokeratoma arises from the proximal nail fold. Although similar in appearance to ADFKs, Koenen’s tumors occur in association with tuberous sclerosis and possess atypical stellate myofibroblasts. Aggressive digital papillary adenocarcinoma, which can be fatal, is the most important condition to exclude from ADFK.

The cause of ADFKs is unknown. While researchers point toward trauma or repetitive irritation, there may be an unknown genetic factor at work. The conditions that most closely resemble ADFKs—supernumerary digits and the periungual fibromas of tuberous sclerosis—have a genetic basis. Reports of ADFKs occurring with a pyogenic granuloma buttresses the idea that trauma relates to their etiology.16

The histology of ADFK is well described. The lesion manifests as a small, well-circumscribed, dome-shaped or narrow elongated papule. The stratum corneum is usually hyperkeratotic, with the hyperkeratosis greatest at the top of the ADFK. An acanthotic epidermis with slightly attenuated or elongated rete ridges is typically found.

The dermal core of an ADFK demonstrates three possible histological patterns.14,17 The most common, type I, consists of a dermal core composed of thick, closely intertwined collagen bundles with numerous capillaries, varying numbers of fibroblasts, and thin elastic fibers oriented along the vertical axis of the lesion.

Type II ADFKs resemble type I but also possess many more fibroblasts arranged in fascicles and greatly reduced numbers of elastic fibers. Type III ADFKs are the least common and possess a dermal core that is poorly cellular and edematous with a reduced number of elastic fibers.

Interestingly, cyclosporine (Gengraf, Neoral, Sandimmune) has been linked to the development of ADFKs.18 Acquired periungual fibrokeratoma developing after acute staphylococcal paronychia has been noted as well.19

ADFK treatment is not complex. Unlike warts, ADFKs cannot be treated with cryotherapy.20 These lesions are usually just a cosmetic problem, and no cases of malignant transformation have been reported. Occurrence in locations at which pressure is constant (e.g., the dorsum or plantar surface of the foot) can cause pain. In such cases, removal has a medical rather than a cosmetic basis. Removal with a shave or simple surgical excision is curative, with recurrence after surgery unlikely. Six months after removal of this patient’s lesion, it had not recurred.

Noah S. Scheinfeld, MD, JD, is assistant clinical professor of dermatology at Columbia University in New York City, where he has a private practice. The author has no relationships to disclose relating to the content of this article.

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All electronic documents accessed July 15, 2011.

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