Dermatofibroma

Dermatofibroma are common and benign skin tumours but frequently cause concern upon discovery.

Traditionally, dermatofibroma were attributed to a reactive reaction to trauma such as insect bites. However, the precise aetiology is unclear. They appear to be clonal proliferative growths of dermal dendritic histiocyte cells.

• More frequent in women than men (ratio of 4:1)
• Can occur at any age, most commonly in young adulthood.

• A solitary lesion on the lower limbs.
• A freely moving, firm to hard nodule of 0.5-1.0 cm diameter, sometimes compared to the feel of a small lentil under the skin surface.
• Overlying epidermis is tethered (the 'dimple' sign).
  
• The skin's surface is generally smooth, occasionally scaly.
• Overlying skin colour varies from skin coloured to pink/red to cream/white to brown.

• Usually a single nodule develops on an extremity, most commonly the lower legs.
• Lesions can occur at any skin site and individuals may have several lesions (up to 15).
• Multiple variants tend to occur where immunity is impaired (e.g. autoimmune disease, SLE, HIV, leukaemia).
• The nodule is usually asymptomatic but can be itchy or tender.
• After initial growth, they tend to remain static in size.

• Diagnosis is usually straightforward provided you palpate the lesion as few other skin lesions are as firm.
• The pinch test is helpful (but not definitive): squeezing the lesion from the sides results in dimpling of overlying skin (see image above).
• With a dermatoscope, dermatofibromas typically show a pigment network and central white patch but there is considerable variation.²
• Excision biopsy is useful where diagnostic uncertainty remains after examination.

Includes:

• Atypical mole
• Basal cell carcinoma
• Keloid or hypertrophic scar
• Keratoacanthoma
• Malignant melanoma
• Metastatic carcinoma of the skin
• Spitz nevus
• Blue nevus
• Squamous cell carcinoma

Deep penetrating dermatofibroma may be difficult to distinguish, even histologically, from rare malignant fibrohistocytic tumours e.g. dermatofibrosarcoma protuberans.³

• Reassure - generally no treatment is required.
• Remove where cosmetically disliked, symptomatic or diagnostic uncertainty. Note that there is a significant local recurrence rate (in about a quarter of patients).
• Removal by elliptical excision or punch biopsy usually provides the most satisfactory results: shave excision or cryotherapy risk incomplete excision and recurrence.
• About 2% GP subcutis excisions yield unexpected or rare malignancies so even where excision is for cosmetic or symptomatic reasons, it is nonetheless worth sending specimens to histology.⁴

• Lesions are almost invariably benign - there are extremely rare case reports of metastasising cellular dermatofibromas although histological distinction from other tumours can prove difficult.⁵ Follow up lesions that are histologically atypical or undergo recurrence.
• Most are static and persist indefinitely although uncommonly they spontaneously regress.
• They may become repeatedly irritated by shaving, for example.

Normally for diagnostic assistance to differentiate from other potentially harmful pigmented lesion.