Page 29 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 2-2 Benign Growths

BECKER’S NEVUS (SMOOTH
MUSCLE HAMARTOMA)

Becker’s nevi most commonly appear on the shoulder
or upper limb girdle of prepubescent boys. It is a rather
common benign condition that is seen in up to 0.5% Becker’s nevus
of the male population. It is less commonly seen in
females. Becker’s nevi are acquired nevi. Most occur
before 10 years of age. Becker’s nevus is classified as a
smooth muscle hamartoma. It does not contain mela-
nocytic nevus cells and is not considered to be a mela-
nocytic nevus. It was given its name by the dermatologist
Samuel Becker, who first described this condition.
Clinical Findings: Becker’s nevi begin as ill-defined,
slightly hyperpigmented macules on the upper limb
girdle. Over time (1 year, on average), the hyperpig-
mented region develops hypertrichosis, resulting in
its characteristic appearance. Backer’s nevi may occur
anywhere on the human body, but by far the most
common locations are on the shoulder, upper chest,
and back. The area of hypertrichosis is limited to the
underlying hyperpigmented area. The clinical signifi-
cance of Becker’s nevi is its differentiation from large
congenital nevi and café-au-lait macules. Becker’s nevi
confer no increased risk for development of melanoma,
and they are rarely associated with any underlying
abnormalities. The most common underlying abnor-
mality is unilateral hypoplasia of the breast, which has
minimal clinical significance. Rarely, a patient with a
Becker’s nevus has underlying hypoplasia of bone and
soft tissue, the cause of which is unknown. The dif-
ferential diagnosis includes a giant congenital nevus
and a café-au-lait macule. These two conditions should
be easily differentiated from Baker’s nevus, because
they both are typically apparent at birth or soon there-
after, whereas Becker’s nevi are typically acquired at
about the age of 10 years.
The diagnosis is typically made on clinical findings,
but a skin biopsy is sometime needed to confirm the
diagnosis if the nevus is in an unusual anatomical
location. The punch biopsy is the best method for
obtaining tissue.
Histology: The biopsy specimen shows a smooth
muscle hamartoma. Multiple smooth muscle fascicles
are seen within the dermis. There is an increased ratio
of terminal to vellus hairs and a lack of melanocytic
nevus cells. The hyperpigmentation results from
increased formation of pigmentation within the mela- Becker’s nevus low power. Mild acanthosis is seen, Becker’s nevus high power. Collagen bundles
nocytes of the stratum basalis. There is no increase in with hyperpigmentation present within the basal surround the prominent adnexal structures.
the number of melanocytes. Varying amounts of acan- cell layer. Prominent sebaceous glands are present.
thosis and hyperkeratosis are seen.
Pathogenesis: The pathogenesis of Becker’s nevus is
unclear. It is believed to be caused by the dermal pres-
ence of hamartomatous smooth muscle tissue. Research Non-Becker’s smooth muscle hamartomas are usually release; rather, it is caused by a neurally mediated con-
has shown that the tissue in Becker’s nevi has an present at birth or soon thereafter and manifest as a traction of the underlying hamartomatous smooth
increased number of androgen receptors. It is thought small, flesh-colored plaque located anywhere on the muscle tissue.
that increased androgen levels at puberty interact with body. All smooth muscle hamartomas may at some Treatment: No therapy is required. Surgical excision
the excessive androgen receptors and cause the clinical point exhibit the pseudo-Darier’s sign. To clinically is likely to produce a mutilating scar unless the nevus
findings. elicit this sign, one gently rubs the smooth muscle is extraordinarily small. The hypertrichosis can be
Becker’s nevus is the most common type of smooth hamartoma; the lesion may fasciculate due to smooth treated for cosmetic purposes with any of a multitude
muscle hamartoma in the skin. Smooth muscle hamar- muscle activity, or the region may develop an urticarial of therapies including laser removal, shaving, and elec-
tomas by themselves are rarely found within the skin. appearance. This sign has nothing to do with histamine trolysis. Most patients prefer to not treat the area.

THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS 15