Dermatofibroma (DF) also referred to as Benign Fibrous Histiocytoma, is a very common skin lesion, described as usually a single round or ovoid papule or nodule, about 0.5 to 1.0 cm in diameter, often reddish brown but sometimes has a yellowish hue. On palpation these lesions are firm and present an abrupt elevation at the border to form an exteriorized tumor resting on a sessile base. They occur in every ethnicity and at any age but seldom in children (most commonly found in middle-aged patients).
Their size varies between 4 to 20 mm, although giant lesions greater than 5 cm have been reported. The most common locations are the lower extremities, above the elbows or on the sides of the trunk. Multiple DFs may be seen. A characteristic on physical examination is that DFs tend to dimple when the skin is pressed around the lesions (see below) and this is called a “positive dimple sign.” HIV infection and patients with chronic myelogenous leukemia have been known to develop multiple dermatofibromas, and I have reported a family with numerous dermatofibromas that appear to be inherited in an autosomal dominant manner (to see reference click HERE). In fact, we studied this family group along with another family group and determined that the genetic defect is Coagulation Factor XIII-A subunit missense mutation in the pathobiology of autosomal dominant multiple DFs. This was published in September, 2019 in the Journal of Investigational Dermatology…to read this article click HERE.
The cause of DFs is unknown, but it is suggested to be caused by blunt force trauma and possibly insect bites. Histologically the dermal mass is composed of close whorls of fibrous tissue in which there are numerous spindled or histiocytic cells. Immunohistochemical studies are remarkable for being positive for factor XIIIa and CD10, and negative for MAC387, S-100, and CD34. In view of our article showing a genetic association with familial DFs and factor XIII-A, it makes sense that factor XIII-A immmunohistochemical studies would be positive.
DIFFERENTIAL DIAGNOSIS (DD): The most significant concern with differentiation is the possibility of dermatofibroma sarcoma protuberans (DFSP), which is a locally aggressive sarcoma, most commonly found on the upper back and shoulder regions. DD also includes Basal Cell Carcinoma and Kaposi Sarcoma. Most of the times these considerations are easy to exclude based on clinical grounds, but at times a punch biopsy may be required.
TREATMENT: These lesions usually are asymptomatic and do not require treatment. Involution may occur after many years if the DFs are left alone. I often discourage my patients to have them surgically removed because the scar will be 3 times the size of the lesion, are permanent and at times the scars can become hypertrophic or keloidal…and now you have a much bigger problem. To read more about DFs click HERE and HERE.