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A 25-year-old woman reports a firm nodule on her leg that gets in the way of shaving her leg (Figure 166-1). Upon questioning, the nodule may have appeared in that location after she cut her leg shaving 1 year ago. She is worried it could be a cancer and wants it removed. Close observation showed a brown halo and a firm nodule that dimpled down when pinched. A diagnosis of a dermatofibroma (DF) was made and the choices for treatment were discussed.
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DF is a benign fibrohistiocytic tumor, usually found in the mid dermis, composed of a mixture of fibroblastic and histiocytic cells. These scarlike nodules are most commonly found on the legs and arms of adults.
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Also called benign fibrous histiocytoma.
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Occurs more often in women (male-to-female ratio is 1:2).1
Found in patients of all races.
Approximately 20% occur in patients younger than age 20 years.1 In one case series, 80% occurred in people between the ages of 20 and 49 years.2
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ETIOLOGY AND PATHOPHYSIOLOGY
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Uncertain etiology—Nodule may represent a fibrous reaction triggered by trauma, a viral infection, or insect bite; however, DFs show clonal proliferative growth seen in both neoplastic and inflammatory conditions.3
The epidermal regions of DFs are similar to seborrheic keratosis in terms of histologic features and activation of fibroblast growth factor receptor 3 and forkhead box N1.4
Multiple DFs (i.e., >15 lesions) have been reported associated with systemic lupus erythematosus, HIV infection, Down syndrome, Graves disease, or leukemia and may represent a worsening of immune function.1 A case of familial eruptive DFs has also been reported associated with atopic dermatitis.5
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Firm to hard nodule; skin is freely movable over the nodule, except for the area of dimpling.
Color of the overlying skin ranges from flesh to gray, pink, red, blue, brown, or black (Figures 166-2 and 166-3), or a combination of hues (Figure 166-4).
Dimples downward when compressed laterally because of tethering of the overlying epidermis to the underlying nodule (see Figure 166-3).
Usually asymptomatic but may be tender or pruritic.
Size ranges from 0.3 to 10 mm; usually less than 6 mm. Rarely, DFs grow to larger than 5 cm.6
May have a hyperpigmented halo and a scaling surface (see Figure 166-4).
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