Continuing Education Activity

Acquired digital fibrokeratoma (ADFK) is a rare, benign, fibrous tumor. It usually occurs in adults as a solitary lesion on fingers and toes. Since ADFK shares clinical and histologic features with other cutaneous conditions, careful examination is necessary for proper diagnosis and management. This activity reviews the evaluation and treatment of ADFK and highlights the role of the interprofessional team in the care of patients with this condition.

Objectives:

• Describe the typical patient history associated with acquired digital fibrokeratoma.
• Explain the treatment modalities of acquired digital fibrokeratoma.
• Review the differential diagnosis for acquired digital fibrokeratoma.
• Summarize the importance of collaboration and communication amongst the interprofessional team to enhance the care of patients with acquired digital fibrokeratoma.

Introduction

Acquired digital fibrokeratoma (ADFK) is a relatively rare, benign, fibrous tumor.[1][2] In 1968, Bart et al. reported 10 cases of this uncommon condition located on the fingers. This lesion can occasionally occur on the lower lip, nose, elbow, pre-patellar area, nail bed, and heel.[3][4] Hence, the name “acral fibrokeratoma” would be more pertinent.[5] This tumor occurs more often in middle-aged adults. The mechanisms that give rise to ADFK are still unknown and probably are heterogeneous.[6] Typically, it appears as a small solitary papule surrounded by a  characteristic hyperkeratotic collarette. Therefore, the differential diagnosis usually includes a rudimentary supernumerary digit and the common wart.[7][8] The treatment of choice is surgical excision of the tumor as ADFK does not show spontaneous involution.

Etiology

The etiology of acquired digital fibrokeratoma remains unclear. It has been proposed to be associated with trauma or chronic irritation, especially in the acral areas.[9] Nevertheless, there are reports of a history of trauma. An infectious origin is also proposed as a possible cause for this condition as reports exist of two cases of ADFK that occurred after a staphylococcal infection.[10][11] Interestingly, there has been one case of ADFK that occurred concurrently with gingival overgrowth after cyclosporin treatment.[12]

Epidemiology

Acquired digital fibrokeratoma is a rarely reported tumor. The actual incidence is still unknown. Most publications related to this condition only concern individual case reports. Usually, the authors stressed the lesions’ unusual size, location, or association with other conditions. A few case series exist. The most significant case series published so far included 50 patients.[1] Documented cases of ADFK appear in patients of all races. Furthermore, reports exist in German, Polish, Japanese, French, and Indian literature.[7] Males seem more affected than females, and the age range is 12 to 70 years.[7]

Pathophysiology

The pathophysiology of acquired digital fibrokeratoma is unknown. Histologically, the tumor is composed of denser fibers than normal skin and contains more fibroblasts and coarser elastic fibers. Therefore, the presumption is that ADFK results from the neoformation of collagen by fibroblasts.[4][7] Nemeth and Penneys reported that factor Xllla, which was present in fibrovascular tumors, was also found in ADFK.[13] Furthermore, collagen synthesis may undergo regulation by factor Xllla-positive dermal dendrocyte, which increases in ADFK. Hence, factor Xllla may play a predominant role in the fibroblastic reaction.[6] In post-staphylococcal ADFK, S. aureus enterotoxin B was shown to increase fibroblasts migration.[14]

Histopathology

Excisional biopsy should be the gold standard for acquired digital fibrokeratoma diagnosis. The histopathological examination typically reveals a very hyperkeratotic and acanthotic epidermis with thick collagen bundles oriented along the vertical axis in the dermis. The dermal core of an ADFK presents one of three histological variants which were characterized by Kint et al.[1] Type I is the most common variant. It presents as a dome-shaped lesion and consists of a dermal core of thick, densely packed collagen bundles with fine elastic fibers.[1] Type II is a mainly tall and hyperkeratotic tumor. It shows more fibroblasts arranged in the cutis than the first type with reduced elastic fibers.[1] Type III is the least common variant. It presents as a flat to dome-shaped lesion with poorly cellular dermal core, edematous structures, and absent elastic fibers.[1]

History and Physical

In most cases, acquired digital fibrokeratoma presents as an asymptomatic protuberance that does not show spontaneous regression.[4] Clinically, it occurs as a solitary, skin-colored, and well-defined papule with a characteristic hyperkeratotic collarette at its base.[15] It usually occurs on the fingers and toes but can also be seen on the lower lip, nose, elbow, pre-patellar area, and periungual tissue.[1][7] The size of the lesion is generally less than 1 cm, but there are reported cases of ADFK more than 1 cm. These lesions were designated as giant ADFKs.[3][7]

Evaluation

The dermoscopic features of acquired digital fibrokeratoma have been rarely investigated and may differ among ADFK cases. Rubegni et al. reported a central homogeneous pale-yellow core fringed by a hyperkeratotic white scaly collarette. These features may reflect the epidermal acanthosis, hyperkeratosis, and the presence of dense collagen fibers. More peripherally, a whitish-yellow area with dotted vessels was evident, while globular vessels externally encircled the whole tumor.[16] Hayashi et al. Reported the presence of red clumped structures divided by white meshwork-like keratotic septa, which may reflect the histologically retracted epidermis.[17]

Treatment / Management

There are reports of diverse therapeutic options, including cryotherapy, shave excision, curettage, and cauterization. However, surgical excision is the mainstay of effective treatment. The tumor should be excised from its basal attachment to prevent recurrences.[18][19]

Differential Diagnosis

It is important to know about the various causes of cutaneous lesions mimicking acquired digital fibrokeratoma so that treatment can commence promptly. The differential diagnosis of ADFK includes supernumerary digit, verrucae vulgaris, cutaneous horn, neurofibroma, and pyogenic granuloma.[7][8][20]

Supernumerary digit, usually found at the base of the fifth finger is one of the most common hereditary limb malformations. Histologically, rudimentary polydactyly differs from ADFK by the presence of nerve bundles and neuroid elements.[5] ADFK can often be mistaken as a supernumerary digit as seen in a case reported by  M. Ali et al., in which the histological report confirmed ADFK of the big toe.[7]

Verrucae vulgaris, also known as common warts, is the most frequently occurring neoplasm of the hand and fingers and is caused by human papillomavirus types 1, 2, 4, and 29.[21] Clinically, common warts often feature a pattern of tiny black dots that correspond to thrombosed capillaries.[22] Yu and Morgan reported a case in which ADFK was misdiagnosed as common warts and recurred after cryotherapy.[8]

A cutaneous horn is a clinical diagnosis referring to an exophytic and hyperkeratotic growth that contains a column of keratin. Histological examination may show a premalignant or malignant underlying process. Cutaneous neurofibromas are benign tumors that may share a clinical resemblance with ADFK and presents as a soft, polypoid, dome-shaped tumor.[23] Histological examination shows loosely spaced spindle cells, wavy collagenous strands, and myxoid matrix.[4][24]

Pyogenic granuloma is a common vascular tumor that usually occurs in areas of minor trauma.[25] Clinically, it presents as a friable, dome-shaped or pedunculated nodule with a scaly collarette. Differential diagnoses may also include superficial acral myxoma, periungual fibroma, and non-pigmented eccrine poroma.[26][27]

Prognosis

Acquired digital fibrokeratoma is a benign tumor with no risk of malignant transformation. Surgical excision is curative with a low risk of pain, bleeding, and infection. Excellent functional recovery with a satisfying cosmetic result is the expectation after complete surgical treatment. Usually, there is no recurrence.[19]

Complications

No reports exist of severe complications. However, a rare variant of acquired digital fibrokeratoma, known as periungual fibrokeratoma may cause nail plate deformity and affect the function of the digit.[15]

Deterrence and Patient Education

There are no preventative measures that can be taken as the etiology is not clear. Patient education should include post-operative instructions to reduce the risk of infection.

Enhancing Healthcare Team Outcomes

The majority of skin lesions first present to primary care providers, including nurse practitioners. However, the number of cutaneous lesions is vast, and the primary care provider cannot know all of them. Thus, it is important to work in collaboration with a dermatologist when faced with an unknown skin lesion. The other important fact is that clinicians should not presume that all skin lesions are benign; missing a malignancy can prove to be devastating for the patient.

Acquired digital fibrokeratoma is most commonly diagnosed based on history and physical examination. Clinicians need to be familiar with unusual manifestations and other skin conditions that may simulate ADFK. Microscopic assessment is often required to provide histological diagnosis and variants. Management of ADFK is possible with a complete surgical excision performed by a dermatologist or a plastic surgeon. The postoperative period involves nurses for incision care and pharmacists for appropriate pain management that could significantly affect the patient's quality of life. If either the pharmacist or the nurse detects any failure in treatment or follow-up, they should report this to the treating clinician. Despite acquired digital fibrokeratoma being a benign lesion, the principles of interprofessional team dynamics are important, as they will always lead to better patient outcomes. [Level 5]