Dermatofibroma

Definition/diagnostic criteria Dermatofibroma, also known as a benign fibrous histiocytoma, is a common benign skin lesion. It is characterised by a firm, hyperpigmented, nodular growth, typically found on the lower extremities. Dermatofibromas are usually asymptomatic but can be tender or pruritic. They often present as a solitary lesion, but multiple lesions can occur. The lesion’s firmness is classically demonstrated by the dimple sign, which occurs when the lesion is pinched.

Epidemiology Dermatofibromas are more prevalent in adults, with a higher frequency in women. They typically appear during middle age but can occur at any age. There is no significant racial predilection. The exact incidence in the UK is not well documented, but they are considered a common dermatological finding in general practice.

Diagnosis
Clinical features: Clinically, dermatofibromas are small, often less than 1 cm in diameter, firm and hyperpigmented. They are most commonly found on the lower legs, but can also occur on the arms and trunk. The lesions are generally painless, although they can be tender or itchy. The dimple sign is a key diagnostic feature.

Investigations: Investigations are rarely needed as the diagnosis is primarily clinical. However, if there is uncertainty, a biopsy can be performed. Histologically, dermatofibromas are characterised by a proliferation of fibroblasts and histiocytes in the dermis, often with overlying epidermal hyperplasia.

It is important to consider differential diagnoses. These include basal cell carcinoma, particularly the nodular type, which can sometimes mimic the appearance of a dermatofibroma but typically presents with a pearly edge and telangiectasia. Melanoma should also be considered, especially in atypical or changing pigmented lesions; features suggestive of melanoma include asymmetry, border irregularity, colour variation, diameter over 6mm and evolving nature.

Other differentials include dermatofibrosarcoma protuberans, a rare, slow-growing soft tissue sarcoma that can be initially mistaken for a dermatofibroma but is more aggressive and requires different management. Seborrheic keratosis and epidermoid cysts are also considerations; these typically have distinct clinical features but can occasionally be confused with dermatofibroma.

Treatment Most dermatofibromas do not require treatment and can be left alone. If the lesion is symptomatic, causes cosmetic concern, or there is diagnostic uncertainty, options include surgical excision or cryotherapy. Excision is curative but can leave a scar, so it should be considered carefully, especially given the benign nature of the lesion. Cryotherapy is less invasive but may not be as effective in completely removing the lesion.

Prognosis The prognosis for dermatofibromas is excellent. They are benign and do not develop into skin cancer. However, they are persistent and rarely resolve spontaneously. Recurrence after removal is uncommon. Patient reassurance about the benign nature of the condition is an important aspect of management.