Dermatofibrom

Synonym: fibrous histiocytoma

What are dermatofibromas?

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

Causes of dermatofibromas (aetiology)

Traditionally, dermatofibromas were attributed to a reaction to trauma such as insect bites. However, the precise aetiology is unclear. Some believe them to be benign neoplasms rather than reactive in origin.

The most common dermatofibromas contain a mixture of fibroblasts, macrophages and blood vessels. Most involve the dermis and may extend to the subcutis. A number of less common variants where the histology differs, such as the aneurysmal fibrous histiocytoma, hemosiderotic fibrous histiocytoma, cellular fibrous histiocytoma and epithelioid fibrous histiocytoma, have been described.¹ Different types are associated with different behaviours and outcomes.

How common are dermatofibromas? (Epidemiology) ²³

• They are common but determining global incidence is challenging as most patients are asymptomatic and do not seek medical attention.

• They are more frequent in women than in men.

• They can occur at any age, most commonly in young adulthood.

• They occur in all ethnicities.

• They are more common and more numerous in those with immunosuppression.

Symptoms of dermatofibromas (presentation)^{3 4}

• 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.

• The skin's surface is generally smooth, occasionally scaly. The overlying skin may be tethered, causing it to dimple when pinched. The skin colour varies from skin-coloured to pink/red to cream/white to brown.

• Dermatofibromas can occur at någon 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.

Dermatofibroma - close-up view

© Mohammad2018, CC BY-SA 4.0, via Wikimedia Commons

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Diagnosis of dermatofibromas

• 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.

• With a dermatoscope, dermatofibromas typically show a pigment network and central white patch but there is considerable variation.⁵ One study noted a difference in dermatoscopy appearance depending on location of the lesion.⁶

• Excision biopsy is useful where diagnostic uncertainty remains after examination.

Differentialdiagnos

Inkluderar:

• Atypical mole.

• Basalcellscancer.

• Keloid or hypertrophic scar.

• Keratoacanthoma.

• Malignt melanom.

• Metastatic carcinoma of the skin.

• Spitz' naevus.

• Blå nevus.

• Skivepitelcancer.

Deep penetrating dermatofibromas may be difficult to distinguish, even histologically, from rare malignant fibrohistiocytic tumours - eg, dermatofibrosarcoma protuberans.⁷

Management of dermatofibromas

• 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.

• Removal by elliptical excision or punch biopsy usually provides the most satisfactory results: shave excision or cryotherapy have higher risks of incomplete excision and recurrence.

A Dutch study showed about 2% of GP subcutis excisions yield unexpected or rare malignancies, and UK studies have shown a lack of reliability in GP diagnosis of skin malignancy.^{8 9} Therefore, even where excision is for cosmetic or symptomatic reasons, it is nonetheless worth sending specimens to histology.

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Referral is normally indicated only for diagnostic uncertainty, to differentiate from other potentially harmful pigmented lesions.

Prognos

• Dermatofibromas are almost invariably benign - there are extremely rare case reports of metastasising cellular dermatofibromas, although histological distinction from other tumours can prove difficult.¹⁰ Follow up lesions that are histologically atypical or undergo recurrence.

• Most are static and persist indefinitely although, uncommonly, they spontaneously regress.

• The cellular type tends to become larger and, as above, has occasionally been reported to metastasise.

• They may become repeatedly irritated - by shaving, for example.