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Synonym: fibrous histiocytoma
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.
- They are more frequent in women than in men (ratio of 4:1).
- They can occur at any age, most commonly in young adulthood.
- Dermatofibromas are usually single nodules that develop on an extremity, most commonly the lower legs. They are freely moving, firm to hard nodules of 0.5-1.0 cm diameter, sometimes compared to the feel of a small lentil under the skin surface.
- The skin's surface is generally smooth, occasionally scaly. The overlying skin may be tethered (the 'dimple' sign). The skin colour varies from skin-coloured to pink/red to cream/white to brown.
- 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, systemic lupus erythematosus, 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.
- Excision biopsy is useful where diagnostic uncertainty remains after examination.
- Atypical mole.
- Basal cell carcinoma.
- Keloid or hypertrophic scar.
- Malignant melanoma.
- Metastatic carcinoma of the skin.
- Spitz' naevus.
- Blue naevus.
- Squamous cell carcinoma.
Deep penetrating dermatofibroma may be difficult to distinguish, even histologically, from rare malignant fibrohistiocytic tumours, eg dermatofibrosarcoma protuberans.
Primary care management
- Reassure - generally no treatment is required.
- Remove where cosmetically disliked, symptomatic or there is 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% of 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.
- Lesions are almost invariably benign - there are extremely rare case reports of metastasising cellular dermatofibromas, although histological distinction from other tumours can prove difficult. 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.
When to refer
Normally for diagnostic assistance, to differentiate from other potentially harmful pigmented lesions.
Further reading & references
- Dermatofibroma, DermNet NZ, July 2011
- Dermatofibroma, Primary Care Dermatology Society; images of typical and atypical dermatofibroma
- Zaballos P, Puig S, Llambrich A, et al; Dermoscopy of dermatofibromas: a prospective morphological study of 412 cases. Arch Dermatol. 2008 Jan;144(1):75-83.
- Pierson JC et al, Dermatofibroma, Medscape, Apr 2010
- Hanly AJ, Jorda M, Elgart GW, et al; High proliferative activity excludes dermatofibroma: report of the utility of MIB-1 in the differential diagnosis of selected fibrohistiocytic tumors. Arch Pathol Lab Med. 2006 Jun;130(6):831-4.
- Buis PA, Verweij W, van Diest PJ; Value of histopathologic analysis of subcutis excisions by general practitioners. BMC Fam Pract. 2007 Jan 26;8:5.
- Bandarchi B, Ma L, Marginean C, et al; D2-40, a novel immunohistochemical marker in differentiating dermatofibroma from Mod Pathol. 2010 Mar;23(3):434-8. Epub 2010 Jan 8.
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Dr Chloe Borton
Dr Hayley Willacy
Dr Hannah Gronow