DERMATOFIBROMA (SCLEROSING HEMANGIOMA)
Dermatofibromas are among the most common types of benign skin growths. Usually, they occur on the extremities, with a predilection for the legs. There is some debate as to whether this is a true neoplasm or an inflammatory reaction.
Clinical Findings: Dermatofibromas are seen almost exclusively in adults, and females tend to be afflicted slightly more often than males. There is no race predilection. Dermatofibromas can range in diameter from 2 mm to 2 cm. They are round or oval. Most often they are solitary, but numerous dermatofibromas may be present in an individual. Dermatofibromas are usually small (4-5 mm), firm, red to slightly purple papules that dimple with lateral pressure. This “dimple sign” is often used clinically to differentiate dermatofibromas from other growths. There are many variations of dermatofibromas clinically. Elevated dome-shaped papules or plaques may be seen. The surface may or may not have a slight amount of scale, and occasionally there is an appearance of hyperpigmentation. On the lower legs of females, they are often excoriated as a result of shaving, and this is often the reason the patient presents for evaluation. Dermatofibromas are most frequently asymptomatic, but they can be slightly pruritic.
If dermatofibromas are numerous and located in many areas of the body, the clinician should consider the association with an underlying immunodeficiency state. There have been reports of multiple eruptive dermatofibromas in patients with systemic lupus erythematosus, human immunodeficiency virus infection, and other immunosuppressive states. The dermatofibromas in these patients have been shown to contain more mast cells.
The differential diagnosis of a dermatofibroma can be broad. If the dermatofibroma does not exhibit the dimple sign, the lesion is often biopsied to help differentiate it from melanocytic nevus, melanoma, basal cell carcinoma, dermatofibrosarcoma protuberans (DFSP), prurigo papules, and other epidermal and dermal tumors.
Histology: Dermatofibromas are made up of a collection of dermal spindle-shaped fibroblasts. Histiocytes and myofibroblasts are also found throughout the lesion. The synonym sclerosing hemangioma arises when numerous extravasated red blood cells are seen within the dermatofibroma. Characteristically, the overlying epidermis is acanthotic with broadening of the rete ridges. The rete ridges are slightly hyperpigmented, and this is sometimes referred to as “dirty feet” or “dirty fingers.” This finding explains the hyperpigmentation seen clinically.
Dermatofibromas stain positively for factor XIIIa and negatively for CD34. This is the opposite of the pattern seen in DFSP. Immunohistochemical staining also provides a marker that can be used to help distinguish the benign dermatofibroma (which stains with stromelysin-3) from the malignant DFSP (which does not). In contrast to DFSP, dermatofibromas do not infiltrate the underlying adipose tissue. Dermatofibromas can push down or displace the adipose tissue, but they never truly demonstrate an infiltrative pattern as does a DFSP. There are numerous histological variants of dermatofibromas.
Pathogenesis: The precipitating factor that initiates the formation of a dermatofibroma is thought to be superficial trauma, such as from a bug bite, which causes the fibrou tissue proliferation. The exact etiology is unknown.
Treatment: Most dermatofibromas are not treated in any manner. Complete elliptical excision with a minimal 1- to 2-mm margin is curative. The resulting scar may be more noticeable than the initial dermatofibroma. There is no evidence to support the routine removal of these common tumors to prevent malignant degeneration into a DFSP.