January 2017 | Case of the Month

The diagnosis is a dermatofibroma.

• A dermatofibroma is a benign skin lesion. The exact aetiology is uncertain, some believe it to represent a traumatic reaction, such as to an insect bite, others believe it is a true neoplasm.
• Young adults are most commonly affected, with a higher prevalence in women. Lesions are generally asymptomatic although can be painful when knocked.
• Distribution
  • Commonly on the limbs, especially the thighs and lower legs
  • Multiple lesions are common
• Morphology
  • Most lesions are approximately 5 mm in size and slightly elevated
  • Colour tends be red to brown. A deeper area of pigmentation can be found at the periphery of the lesion
  • Palpation reveals that much of the lesion sits deep to the skin surface and has a firm consistency
  • Pinching the lesion results in central dimpling
  • Some lesions are larger and much more nodular in appearance
• Dermoscopic appearance
  • The appearance of a central scar-like white area associated with a very fine, brown, peripheral rounded network is very characteristic
  • Early / flat lesions may have little in the way of a central white area

In this case the central white area also had a white network, which is a feature seen in some dermatofibroma. A white network (sometimes called an inverted pigment network) can occasionally be seen in melanoma, however, in this case the clinical presentation with a firm underlying lump, overall symmetry and central white network were all consistent with a dermatofibroma. In melanoma one would expect to see significant asymmetry both clinically and dermoscopically.

Please refer to the chapter on dermatofibroma for more information.