When A Large Multicolored Nodule Arises On The Anterior Shin

An 88-year-old African-American female presented to the clinic for a diabetic foot checkup. As I was obtaining the patient’s medical history, she brought attention to a large nodule on her anterior right shin. It had been present for a while but she didn’t know exactly how long. She also didn’t remember how the nodule had begun but was sure there was no trauma or other inciting event. The lesion wasn’t painful. It was just unsightly and concerning due to its large size. It was not growing rapidly. She had no personal or family history of skin cancer.

Upon conducting the physical exam there, I noted an elevated 1 cm nodule on the anterior right ankle. It was firm and circular, but with various shades of brown and red. The surrounding skin was not erythematous. There was also some central dimpling. The patient expressed no pain on palpation but she wanted the lesion removed regardless. I performed a shave biopsy and sent it to pathology for histological examination, which showed epidermal hyperplasia, subtle spindle cell proliferation in the underlying dermis, and splicing between collagen bundles.

Key Questions To Consider

1. What is the diagnosis?
2. What is the malignant form of this lesion?
3. What is the etiology?
4. What are the main diagnostic clues?
5. What are the treatment options?

Answering The Key Diagnostic Questions

1. Dermatofibroma
2. Dermatofibrosarcoma protuberans
3. Unknown but likely trauma
4. Central dimpling, delicate peripheral pigment network and central scar-like white patch on dermoscopy, epidermal hyperplasia
5. Steroid injections, cryotherapy, excision

What You Should Know About Dermatofibromas

The dermatofibroma is defined as a “fibrosing cutaneous lesion characterized by an increased number of fibrocytes in the dermis and occasionally subcutis.”¹ Researchers did not recognize dermatofibromas as a clinical entity until 1970 with the development of immunochemistry techniques and electron microscopy.²

Although the exact etiology is unknown, they are frequently associated with trauma and even bug bites.³ These lesions are very common and most frequently affect young or middle-aged adults with a slight predominance in females. They have a predilection for the lower extremities and particularly the anterior shin with an incidence as high as 83 percent in some studies.¹ Other names for this lesion include benign fibrous histiocytoma, sclerosing hemangioma, xanthogranuloma, fibroxanthoma and nodular subepidermal fibrosis.²

Essential Diagnostic Insights

Although they may persist for years and even indefinitely, these lesions are completely benign. They appear as firm papules or nodules with a smooth or dome-shaped surface and various colors, including dark brown, purple-red or yellow. They are very common and can range in size from a few millimeters to 2 cm. They are commonly confined to the epidermis and dermis but, in rare instances, can extend into subcutaneous tissues.

This is in contrast to dermatofibroma’s malignant counterpart, dermatofibrosarcoma protuberans, which arises from deeper dermis and aggressively invades the subcutaneous tissue. Most of the time, benign dermatofibromas are asymptomatic but can be painful or pruritic at times.⁴

One of the most helpful diagnostic clues in the physical exam is the “dimple sign,” which occurs when lateral palpation and compression of the lesion produce invagination of the lesion.⁵ Dermoscopy can also be very helpful, most often showing a delicate pigment network on the periphery of the lesion with a central scar-like white patch.1 If one obtains a biopsy, it will show a triad of epidermal changes, including hyperkeratosis, acanthosis and basal layer hyperpigmentation.³

Pertinent Pearls On Treating Dermatofibromas

Excision is curative for these lesions, whether it is through a punch or shave biopsy, or through a formal procedure such as an elliptical incision. Physicians must remember that this lesion extends down into the dermis and possibly the subcutis so a simple superficial shave biopsy may not suffice. Additionally, the excision itself may leave a scar, which can be problematic if the patient’s main concern is cosmetic.

For this reason, some have suggested other less invasive treatments that will leave less of a scar, such as intralesional steroid injections or even cryotherapy.⁵ Performing steroid injections would be intuitive given their common use in treating other fibrotic skin lesions like hypertrophic scars and keloids. As for cryotherapy, there are limited studies showing its efficacy and tolerability. For example, Lanigan and colleagues treated 35 dermatofibromas in 27 patients with cryotherapy.⁶ The overall response to therapy as assessed by the patients was excellent or good for 32 of 35 dermatofibromas with most patients agreeing the cosmetic outcome was preferred over biopsy. However, multiple treatments were required in more than half of the patients, which is not the case with a biopsy or excision.

Given the benign nature of this lesion, simple monitoring is perfectly reasonable. Some patients may not want the risk of a biopsy or the pain of cryotherapy or injections. Should the lesion show signs of malignant transformation such as recent and rapid modification with irregular borders or multinodular appearance, a biopsy is indicated along with possible referral to oncology.

When A Dermatofibroma Turns Malignant: Dermatofibrosarcoma Protuberans

The malignant form of a dermatofibroma is dermatofibrosarcoma protuberans, a rare tumor with an incidence of 1:100,000 per year with an equal distribution between males and females.⁷ The age at diagnosis is between 20 and 59 for most patients. A chromosomal translocation is present in more than 90 percent of cases. Dermatofibrosarcoma protuberans is a locally aggressive tumor with a tendency for local recurrence but it rarely metastasizes. Accordingly, the five-year relative survival rates are high at 98 to 100 percent. Despite this, patients may present with large tumors due to the diagnosis frequently being delayed.

As metastases are extremely rare, an extensive workup is usually not necessary unless patients have recurrent disease, features of fibrosarcomatous transformation or clinical suspicion of metastasis. As I mentioned before, despite low rates of metastasis, local recurrence is quite common (0 to 40 percent) with dermatofibrosarcoma protuberans. Treatment for dermatofibrosarcoma protuberans is mainly surgical as well, involving wide local excision or possibly Mohs micrographic surgery.⁷

Dr. Vella is in private practice in Gilbert, Ariz.

References

1. Zaballos P, Puig S, Llambrich A, et al. Dermoscopy of dermatofibromas: a prospective morphological study of 412 cases. Arch Dermatol. 2008; 144(1):75-83.
2. Kaur H, Kaur J, Gill KS, et al. Subcutaneous dermatofibroma: a rare case report with review of literature. J Clin Diag Res. 2014; 8(4):FD01-02.
3. Han TY, Chang HS, Lee JHK, et al. A clinical and histopathological study of 122 cases of dermatofibroma (benign fibrous histiocytoma). Ann Dermatol. 2011; 23(2):185-192.
4. Habif TP. Dermatofibroma. In: Clinical Dermatology: A Color Guide to Diagnosis and Therapy, Fifth Edition, Mosby Elsevier, St. Louis, 2010, p. 787.
5. Vlahovic T, Schleicher S. Skin Disease of the Lower Extremities: A Photographic Guide. HMP Communications, Malvern, PA, 2012.
6. Lanigan SW, Robinson TW. Cryotherapy for dermatofibromas. Clin Exp Dermatol. 1987; 12(2):121-123.
7. Saiag, PP. Diagnosis and treatment of dermatofibrosarcoma protuberans: European consensus-based interdisciplinary guideline. Eur J Cancer. 2015; 51(17):2604-2608.