Dermatofibroma

Dermatofibroma are one of the most common 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.

Most commonly:

• Solitary lesion on the lower limbs
• Freely moving, firm to hard nodule of 0.5-1.0 cm diameter - feels like a small lentil under the skin surface
• Tethering of overlying epidermis ('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 (eg 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). 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 eg dermatofibrosarcoma protuberans.²

• Reassure - generally no treatment is required.
• Remove where cosmetically disliked, symptomatic or diagnostic uncertainty.
• Removal by elliptical excision or punch biopsy usually most satisfactory: 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 worth sending specimens to histology.³

• Lesions are benign.
• Most are static and persist indefinately 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 lesions.