Can You Identify the Asymptomatic Nodule on This Man’s Index Finger?

Authors:
Alexander K. C. Leung, MD, and Benjamin Barankin, MD

Citation:
Leung AKC, Barankin B. Can you identify the asymptomatic nodule on this man’s index finger?. Consultant. 2017;57(7):425-426,428.

A 47-year-old man presented with a solitary nodule on the right index finger. He had first noted the nodule 3 years ago. The size of the lesion had increased slowly for the initial 1 to 2 years; it had stabilized in the past year. The nodule was asymptomatic and did not bleed. He was unable to recall any trauma to the region. His past heath was unremarkable. Family history was noncontributory; in particular, there was no family history of tuberous sclerosis or similar skin tumors.

Physical examination revealed a flesh-colored, firm, hyperkeratotic, dome-shaped nodule on the lateral aspect of the right index finger. A surrounding collarette of raised skin encircled its base. The mass measured 4 mm in diameter. It was well demarcated, nontender, and nonpulsatile. The rest of the examination findings were essentially unremarkable.

Answer on next page

Answer: Acquired digital fibrokeratoma

A clinical diagnosis of acquired digital fibrokeratoma was made. Complete surgical excision of the mass was subsequently performed. Histologic examination of the excised lesion showed that the epidermis was hyperkeratotic and acanthotic with thickened rete ridges. The dermis was composed of thick collagen bundles with dilated capillaries oriented parallel to the longitudinal axis of the lesion. These microscopic findings were consistent with those of acquired digital fibrokeratoma. There was no recurrence of the lesion at 1 year’s follow-up.

Acquired digital fibrokeratoma, also known as acquired periungual fibrokeratoma or acral fibrokeratoma, is a benign fibroepithelial tumor characterized histologically by a fibrous core with thick keratotic epithelium and characterized clinically by an acquired, solitary, asymptomatic, skin-colored papule/nodule on an acral extremity.¹ Characteristically, the lesion is surrounded by a collarette of slightly raised skin. Bart and colleagues first described the condition and coined the term acquired digital fibrokeratoma in 1968.²

Epidemiology and Etiopathogenesis

The exact incidence is not known, as information on this condition is mainly limited to case reports. Suffice it to say that it is a relatively uncommon benign skin tumor.^1,3 There is no racial or geographic predisposition.⁴ There is a slight male preponderance.^1,3,4 Most cases occur between the ages of 31 and 60 years, with a peak at 40 years of age.^3,5

The exact etiopathogenesis is not known. Repetitive irritation, trauma, collagen neoformation by fibroblasts, and factor XIIIa are believed to play roles.^4,6 The condition has been reported following treatment with cyclosporine.⁷

Histopathology And Clinical Manifestations

Histologic findings include hyperkeratosis, acanthosis, and elongated rete ridges in the epidermis and a dermal core composed of thick interwoven bundles of collagen fibers with dilated capillaries oriented in the direction of the longitudinal axis of the dermis.^5,8,9 Elastic fibers, if present, are thin and sparse.⁵

An acquired digital fibrokeratoma typically presents as an asymptomatic, well-circumscribed, slow-growing, dome-shaped papule or nodule or, less commonly, elongated finger-like protrusion. Characteristically, the lesion is surrounded by a hyperkeratotic collar or a collarette of slightly raised skin, thereby creating a moat-like configuration.^3,4 The lesion may be pink, tan, or flesh-colored.¹⁰ The surface may be smooth or hyperkeratotic.¹⁰ The size is usually 3 to 5 mm in diameter and typically less than 1 cm in diameter, although giant lesions have also been reported.^4,6,10 Sites of predilection include the finger and toe.⁴ Occasionally, it can occur elsewhere in other acral areas such as the palm, sole, wrist, elbow, and ankle, to which the term acral fibrokeratoma aptly applies.³ The lesions are usually solitary.^4,10 Multiple lesions have rarely been reported.⁵ By definition, the lesion is not present at birth but appears later in life.

Diagnosis and Differential Diagnosis

The diagnosis of acquired digital fibrokeratoma is mainly clinical based on characteristic physical features. The diagnosis can be aided by dermoscopy, which shows clumps of homogeneous red lacunae surrounded by white meshwork-like keratotic septa with underlying telangiectasia.⁹

The differential diagnosis includes periungual fibroma (Koenen tumor), digital mucous cyst, giant cell tumor of the tendon sheath, ganglion, superficial acral fibromyxoma, corn, cutaneous horn, verruca vulgaris, acrochordon, epidermal inclusion cyst, dermatofibroma, neurofibroma, schwannoma, rudimentary supernumerary digit, glomus tumor, porocarcinoma, poroma, enchondroma, pyogenic granuloma, hemangioma, onychomatricoma, aggressive digital papillary adenocarcinoma, and basal or squamous cell carcinoma.^8,11,12

Complications and Prognosis

The condition is cosmetically unsightly. Ulceration of the skin over the tumor can result in infection. Giant lesions may cause discomfort and pain and can affect patient mobility if they occur on the foot.⁴

The lesion is benign and does not have malignant potential. However, without treatment, the lesion tends to persist, as spontaneous regression does not occur.^4,13

Management

Complete surgical excision of this benign tumor is curative and is therefore the treatment of choice.^1,6 Local recurrence can occur with incomplete excision of the tumor.¹³ 

Alexander K. C. Leung, MD, is clinical professor of pediatrics at the University of Calgary and a pediatric consultant at the Alberta Children’s Hospital in Calgary, Alberta, Canada.

Benjamin Barankin, MD, is a dermatologist and the medical director and founder of the Toronto Dermatology Centre in Toronto, Ontario, Canada.

REFERENCES:

1. Boffeli TJ, Abben KW. Acral fibrokeratoma of the foot treated with excision and trap door flap closure: a case report. J Foot Ankle Surg. 2014;53(4):​449-452.
2. Bart RS, Andrade R, Kopf AW, Leider M. Acquired digital fibrokeratomas. Arch Dermatol. 1968;97(2):120-129.
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