A 25-year-old woman reports a firm nodule on her leg that gets in the way of shaving her leg (Figure 160-1). Upon questioning, the nodule may have started there 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.

DF is a benign fibrohistiocytic tumor, usually found in the mid dermis, composed of a mixture of fibroblastic and histiocytic cells. These scar-like nodules are most commonly found on the legs and arms of adults.

Also called benign fibrous histiocytoma.

• Occurs more often in women (male-to-female ratio is 1:4).1
  
• Found in patients of all races.
  
• Approximately 20% occur in patients younger than age 17 years.1 In one case series, 80% occurred in people between the ages of 20 and 49 years.2

• 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
  
• 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.4

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 160-2 and 160-3), or a combination of hues (Figure 160-4).
  
• Dimples downward when compressed laterally because of tethering of the overlying epidermis to the underlying nodule (Figure 160-3).
  
• 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.5
  
• May have a hyperpigmented halo and a scaling surface (Figure 160-4).
  
• DFs can rarely be located entirely within subcutaneous tissue.6

Imaging

• Dermoscopy is a useful adjunctive diagnostic technique for DF (Figure 160-5). Although the most common finding is a ­peripheral pigment network with a central white area (34.7% of cases), 10 dermoscopic patterns have been identified; in a large case series, pigment network was observed in 71.8% (3% atypical pigment network).7 (See Appendix C: Dermoscopy.)