Dermatofibroma

Background

• Common benign lesion- fibrous histiocytoma
• Most commonly occur in females; legs and arms; can develop over areas of trauma or after an insect bite (however, exact aetiology is unknown)
• Persist for years but can resolve
• Multiple lesions can occur in immunosuppressed individuals

Appearance/Presentation

• Firm nodules; yellow-brown or pink in colour (can be quite dark)
  • The skin is usually tethered to the lesion (if pinched- a dimple will form)
• After initial growth, they will remain static in size.
• Not normally symptomatic- but can be mildly itchy or tender
• On examination with a dermatoscope, they can show a pigmented network with a central white region (however, this is highly variable)

For images, see here

Investigation

• Not routinely required (classical ‘firmness’ and benign appearance), but biopsy may be used if there is any uncertainty e.g. if the patient has traumatised the lesion- it may appear similar to a BCC.  Where at all uncertain, it is worth sending a biopsy.
• Histopathology can identify the poorly defined proliferation of ‘fibrohistiocytic’ cells within the dermis with an overlying ‘Grenz’ zone of sparing.  Commonly, there is also collagen trapping at the periphery of the lesion.  The overlying epidermis can be acanthotic with increased basal cell pigmentation.  Occasionally there may also be features of ‘basaloid induction’ of the overlying epidermis i.e. the appearance of small BCC/benign tumours.
  • Histopathology can also go further to subclassify dermatofibroma, some of which can be invasive/malignant and require excision:
    • Cellular type; epitheloid type; aneurysmal type; atypical type (usually recommend excision as it can be aggressive); haemosiderotic type; lipidised type; pallisading type; atrophic type; fibrocollagenous type; clear cell type; deep fibrous type (this last one can be serious but is much rarer)

Management

• The vast majority just require reassurance and no treatment.
• The lesion may be excised if there is a suspicion of malignancy or if the patient is concerned about cosmetic appearance
  • NB Beware that there is a relatively high local recurrence rate