Treating A Pigmented, Slightly Pruritic Nodule

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Key Questions to Consider

1. What essential question does one still need to ask to help make the diagnosis?

2. What is the tentative diagnosis?

3. Can you list at least three differential diagnoses?

4. In regard to the differential diagnosis, what features of this condition differentiate it from other conditions?

5. What is the suitable treatment of this condition?

Answering The Key Diagnostic Questions

1. Do you recall any previous injury, insect bite or other problems in the area of the lesion?

2. The most likely diagnosis is a solitary dermatofibroma
(fibrohistiocytoma).

3. The differential diagnosis includes but is not limited to epidermal cyst, keloid scar, prurigo nodularis, basal cell carcinoma, dermatofibrosarcoma protuberans, foreign body granuloma and insect bites and stings.

4. The condition is characterized by skin lesions that are papular or nodular, firm, raised, round-to-oval and pigmented. They usually retract beneath the skin surface when one squeezes them from either side. This is called the Fitzpatrick Dimple Sign.

5. Treatment is usually not necessary but when these lesions are symptomatic or problematic, one needs to remove them surgically. However, since they are deep, this usually leaves a visible hyperpigmented scar. Cryotherapy may eliminate much of the color of the lesion. It may also flatten and reduce the size of the lesion. Cortisone injections using 4 mg/mL of dexamethasone sodium phosphate may also be helpful.

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Author(s): 
By G.“Dock” Dockery, DPM, FACFAS

Most dermatofibromas remain unchanged for many years or even continue indefinitely. There are infrequent reports of spontaneous regression of dermatofibromas. When this occurs, it may yield a postinflammatory hypopigmentation response. There are rare reports of the uncommon occurrence of dermatofibromas and melanocytic lesions (melanomas) arising in the same biopsy specimen.

A Guide To The Differential Diagnosis

Epidermal cyst. The common epidermal inclusion cyst occurs secondary to trauma with implanted epidermis within the dermis. The cysts may have a thin epidermal cover with small blood vessels visible in the dome or they may have a very thick epidermal cover with overlying hyperkeratotic tissue. Lateral squeezing causes the lesion to enlarge and bulge outward. This lesion grows slowly and may spontaneously drain.

Keloid scar. Keloid scars typically proliferate and extend into normal surrounding skin. The borders are distinct but irregular or bizarre in outline. In some cases, the scar may appear as a hyperpigmented nodular lesion. Keloid scars are very resistant to all forms of treatment, especially surgical excision.

Solitary prurigo nodularis. Solitary prurigo nodularis is an uncommon lesion that presents as extremely pruritic nodules with the most common location on the extensor aspects of the extremities. They are caused by chronic, repetitive picking and rubbing. In generalized prurigo nodularis, there are multiple nodules. Lesions tend to be symmetrical and are associated with excoriations due to the intense pruritus that is present. Many authorities believe this to be a variant of lichen simplex chronicus or a nodular form of neurodermatitis circumscripta.

Basal cell carcinoma. The most common form of basal cell carcinoma, the nodular form, begins as a small, white, dome-shaped nodule or papule. As it expands, telangiectatic vessels become more prominent and the tumor may appear erythematous. The center of the lesion may ulcerate and bleed, and then it never seems to heal. As with other forms of carcinoma, basal cell carcinoma may mimic many other forms of skin lesions.

Dermatofibrosarcoma protuberans. This lesion is a relatively uncommon soft tissue neoplasm with intermediate to low grade malignancy and is a very slow growing tumor. Due to the slow progression and rarity of this condition, the diagnosis is often delayed. It may start as a small asymptomatic papule, which is likely ignored. The tumor may gradually enlarge into a lumpy nodule or it may evolve into an atrophic and/or sclerotic plaque. When encountering an atypical scar-like lesion, the clinician should consider a skin biopsy.

Foreign body granuloma. A benign foreign body granuloma is characterized by a simple macrophage reaction to a penetrating foreign body into the dermis. Normally, the foreign body cannot be broken down or rejected, and is eventually surrounded by foreign body giant cells and walled off. This creates a solid granuloma that is difficult to differentiate from scar and dermatofibroma.

Insect bites and stings. These may involve any area of the body but are common on the arms and legs. Most bites are on the dorsum of the hand and foot rather than the palmoplantar surfaces. The resultant lesion may appear to be raised or nodular. In most cases, the reactions from bites are much more erythematous and inflamed than one would find with a dermatofibroma.

Other painful tumors. One may remember painful tumors of the skin by using the mnemonic: LEND AN EGG for leiomyoma, eccrine spiradenoma, neuroma, dermatofibroma, angiolipoma, neurilemmoma, endometrioma, glomus tumor and granular cell tumor.

Key Insights On The Treatment Of Dermatofibromas

No treatment is necessary for most dermatofibromas. However, most patients tend to want something done to remove them. For lesions that are cosmetically undesirable or those that are symptomatic, or have changed clinical appearances in any way, there are treatment options.

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