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PATIENT STORY

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.

FIGURE 166-1

Dermatofibroma on the leg of a 25-year-old woman that may have begun after she cut her leg shaving 1 year ago. Note the brown halo, pink hue, and raised center. (Reproduced with permission from Richard P. Usatine, MD.)

INTRODUCTION

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.

SYNONYMS

Also called benign fibrous histiocytoma.

EPIDEMIOLOGY

  • 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

ETIOLOGY AND PATHOPHYSIOLOGY

  • 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

DIAGNOSIS

CLINICAL FEATURES

  • 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).

  • DFs can rarely be located ...

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