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 fibrous 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.
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