CASE #1: Dermatofibroma

Usually seen on the legs of young women, dermatofibromas (DFs) manifest as purple papules that dimple inward when squeezed (the dimple sign). Whether DFs are neoplasms or a reactive process remains a matter of debate, but the evidence suggests that they are benign neoplasms. The proximate etiology of most DFs seems to be insect bite or skin trauma secondary to shaving. Also known as fibrous histiocytomas or sclerosing angiomas, DFs are among the lesions most commonly seen in dermatology practices.

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DFs occur more often in women than in men by a ratio of 4 to 1. While the patients most commonly affected appear to be women between the ages of 20 and 40 years, an estimated 20% of DFs occur in persons younger than 20.

While DFs are usually purple, they can manifest in a range of colors, including blue, brown, gray, orange, pink, mauve, red, yellow, or black as well as combinations thereof. DFs typically range in size from 0.3 cm to 1.5 cm, with 0.5-0.7 cm being the most common size. DFs can be ulcerated or eroded. Variants include giant (>5 cm in diameter), atrophic, and atypical polypoid DF, as well as DF with satellitosis. Clinical diagnosis is made by squeezing to elicit a dimple sign or by dermoscopy revealing a peripheral pigmentary network with a central white area.

Most commonly seen on the legs, DFs can occur on the arms, hands, and torso. They are rarely found on the face. DF-like lesions on areas other than the legs or arms should prompt consideration of other diagnoses.

Histologically, DFs are formed from dermal dendritic histiocyte cells. The overlying epidermis demonstrates acanthosis. Pseudoepitheliomatous hyperplasia and proliferation of basal cells can occur. Increased pigment, likely iron or melanin, can be observed. Most lesions display a grenz zone of normal papillary dermis overlying the fibrous cells. DFs usually demonstrate whorling fascicles of a spindle cell proliferation, with excessive collagen deposition wrapping around normal collagen bundles at the periphery.

Immunohistochemical testing of most DFs reveals antibodies to factor XIIIa. Transforming growth factor- signaling may underlie the fibrosis of DF. Histopathologic variants are numerous and include cellular, sclerotic fibroma­like (different from a sclerotic fibroma), aneurysmal, epithelioid, atypical, palisading, and cholesterotic DF; on the hands and feet, myxoid and schwannomalike variants have been noted.

Multiple DF is defined as manifestation of 15 or more DFs. Conditions associated with multiple DFs include lupus and HIV.1 Eruptive DFs is the term used to describe the sudden development of DFs. Eruputive DFs have been associated with immunosuppression from drugs, e.g., efalizumab; neoplasms, such as Sézary syndrome; multiple IgA myeloma; chronic myelogenous leukemia; and diseases involving immunosuppression, e.g., HIV and lupus.2

The differential diagnoses for DF include keloid, basal cell carcinoma, blue nevi, prurigo nodularis, Spitz nevi, sclerotic fibroma, multinucleate cell angiohistiocytoma, and pilomatricoma. The painful tumors of skin can also imitate DF; these include blue rubber bleb nevus, leiomyoma, eccrine spiradenoma, neuroma, DF, angiolipoma, neurilemoma, endometrioma, glomangioma, and granular cell tumor. Dermatofibrosarcoma protuberans (DFSP), which is usually factor XIIIa-negative and CD34-positive, is also on the list of differential diagnoses. A slow-growing but insidious neoplasm, DFSP may be the most important condition requiring rule out.

DFs not associated with any symptoms can be left untreated. The most frequently reported symptoms are pruritus and tenderness. DFs are likely the most common of all painful tumors. For symptomatic DF, treatment with liquid nitrogen can be attempted; if several such treatments fail, intralesional steroid injections (2-3 mg/cc) or shaving the lesions can be attempted. Surgery on the lower legs of young women often results in a suboptimal cosmetic result and should be considered carefully before being attempted. Ablative laser treatment has been reported but is rarely used.

Because the patient was not bothered by the lesion, we decided to provide reassurance and not pursue any additional therapy.