Dermatofibroma

Dermatofibromas (also known as histiocytomas) are common benign fibrous skin lesions. They are caused by the abnormal growth of dermal dendritic histiocyte cells often following a precipitating injury. Common areas include the arms and legs and occurs more often in women.

Etiology: 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.

Pathology: 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. Different types are associated with different behaviours and outcomes.

Clinical Signs and Symptoms: Dermatofibromas are most often found on the arms and legs of women. They are small brown or reddish-brown mobile nodules, and they feel quite firm. They may be tender to touch. Many lesions demonstrate a "dimple sign," where the central portion puckers as the lesion is compressed on the sides. They generally do not change in size.

Differential diagnosis includes:

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

Diagnosis: is usually straightforward provided the doctor palpates 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.One study noted a difference in dermatoscopy appearance depending on location of the lesion.
• Excision biopsy is useful where diagnostic uncertainty remains after examination.

Management: 

• No treatment is usually necessary for dermatofibromas. Simple reassurance that the lesion is benign may be indicated, unless one of the aggressive subtypes is suspected or diagnosed.
• Intralesional steroid injections have been attempted with variable results.
• For cosmetically unacceptable lesions, those that are particularly symptomatic, if there is any diagnostic uncertainty, or when one of the aggressive subtypes is suspected, complete excision, including the subcutaneous fat, is the ideal procedure.
• Superficially shaving the lesion or cryosurgery can be attempted for cosmesis or to decrease the symptoms; however, recurrences are more likely
• If the dermatofibroma is not removed and significant change occurs in the color, size, border, or symptoms, the patient should seek follow-up evaluation.

Prognosis: Typical superficial dermatofibromas are considered benign lesions, and the prognosis for patients with this condition is excellent. However, discomfort from pain or itching may be significant.

Deep, cellular, aneurysmal (hemosiderotic), and atypical variants, which are notoriously more locally recurrent (≤20% of cases), can rarely metastasize.