A 43-year old man presented with a skin lesion on his right shin. The lesion had been present for at least 2 years but had changed recently becoming a little darker around the edge. The lesion was otherwise asymptomatic. There was no other relevant personal or family history.
The lesion was a 7 mm circular macule, which had a skin coloured centre, and a darker brown periphery. A firm, regular lump could be palpated under the skin.
What is the diagnosis - only the dermoscopic image is provided?
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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.
- Commonly on the limbs, especially the thighs and lower legs
- Multiple lesions are common
- 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
- 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.