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.
