Dermatofibroma

Dermatofibroma, also known as dermal dendrocytoma, benign fibrous histiocytoma, and several other names, is a benign nodule that typically forms on the skin of adults. The common sites for these nodules are the legs, elbows, and chest. These lesions are usually painless and have a diameter ranging from 0.2 cm to 2 cm, although larger examples have been reported. Dermatofibromas often result from minor trauma, such as insect bites. Risk factors for developing multiple dermatofibromas include conditions like lupus, HIV, blood cancer, and the use of immunosuppressive medicines.

Signs and Symptoms

Dermatofibromas present as hard, solitary, slow-growing papules that can appear in a variety of colours, most commonly brownish to tan. These nodules are often elevated or pedunculated. One characteristic feature of dermatofibromas is the "dimple sign": applying lateral pressure to the nodule causes a central depression. Although most dermatofibromas cause minimal to no discomfort, some may be associated with itching and tenderness.

These lesions can occur anywhere on the body, but they are most frequently found on the legs and arms. Dermatofibromas are more common in women, with a male to female ratio of about 1:4. They typically appear in adults aged 20 to 45 years.

Some researchers believe that dermatofibromas form as a reaction to previous injuries such as insect bites or thorn pricks. They are composed of disordered collagen laid down by fibroblasts and are classified as benign skin lesions. However, they can be confused with various subcutaneous tumours. Deep-penetrating dermatofibromas may be difficult to distinguish from rare malignant fibrohistocytic tumours like dermatofibrosarcoma protuberans.

Diagnosis

Diagnosis of dermatofibroma is generally based on its appearance. A central dimpling upon lateral pressure, known as the buttonhole sign, is a diagnostic feature. However, to rule out other similar-looking conditions such as granular cell tumours, melanoma, clear cell acanthoma, and dermatofibrosis lenticularis disseminata, a biopsy may sometimes be required.

Immunohistochemical Staining

Immunohistochemical staining is used to differentiate dermatofibromas from other neoplasms. The following markers are typically assessed:

• CD34: Negative in dermatofibromas but positive in dermatofibrosarcoma protuberans.
• Stromelysin-3: Positive in dermatofibromas.
• Factor XIIIa: Positive in dermatofibromas.

Neoplasm	CD34	Stromelysin-3	Factor XIIIa
Dermatofibroma	-	+	+
Dermatofibrosarcoma protuberans	+	-	-

Treatment

Most dermatofibromas do not require treatment as they are benign and harmless. The lesions can remain unchanged for years, and in some cases, they may resolve spontaneously. If a dermatofibroma causes significant discomfort or cosmetic concern, treatment options include surgical excision or cryotherapy. Nonetheless, it is essential to differentiate dermatofibromas from other potentially malignant tumours to ensure appropriate management.

Specialty

Dermatofibromas fall under the specialty of oncology, despite being benign, due to the necessity of distinguishing them from malignant lesions. Dermatologists and oncologists often collaborate in diagnosing and managing these lesions.

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Self-assessment MCQs (single best answer)

What is the typical diameter range of dermatofibromas?

Which of the following signs is characteristic of dermatofibromas?

What risk factor is associated with the development of multiple dermatofibromas?

Which gender is more commonly affected by dermatofibromas?

What is the male to female ratio for the occurrence of dermatofibromas?

Dermatofibromas are composed of disordered collagen laid down by which type of cells?

Which immunohistochemical marker is positive in dermatofibromas but negative in dermatofibrosarcoma protuberans?

What is the main reason dermatofibromas generally do not require treatment?

Which specialty typically handles the diagnosis and management of dermatofibromas?

What feature distinguishes dermatofibromas from dermatofibrosarcoma protuberans in immunohistochemical staining?