Becker's
Nevus (Smooth Muscle Hamartoma)
Becker's nevi most commonly appear
on the shoulder or upper limb girdle of prepubescent boys.
common benign condition
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 melanocytic nevus cells and is not considered to
be a melanocytic 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), thehyperpigmented 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
significance of Becker's nevi is its differentiation from large congenital nevi
and café-au-lait macules.These two conditions should be easily differentiated from Baker's nevus, because they both are typically apparent at birth or soon thereafter, whereas Becker's nevi are typically acquired at about the age of 10 years.
Becker's nevi confer no increased risk for
development of melanoma, and they are rarely associated with any underlying
abnormalities.
The most common underlying abnormality is unilateral hypoplasia of
the breast, Rarely, a patient with a
Becker's nevus has underlying hypoplasia of bone and soft tissue, the cause of
which is unknown.
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.
Pathogenesis: The pathogenesis of Becker's nevus is unclear.
All smooth muscle
hamartomas may at some point exhibit the pseudo-Darier's sign. To clinically
elicit this sign, one gently rubs the smooth muscle hamartoma; the lesion may
fasciculate due to smooth muscle activity, or the region may develop an
urticarial appearance. This sign has nothing to do with histamine release;
rather, it is caused by a neurally mediated contraction of the underlying
hamartomatous smooth muscle tissue.
Treatment: No therapy is required. Surgical excision is likely to
produce a mutilating scar unless the nevus is extraordinarily small. The
hypertrichosis can be treated for cosmetic purposes
laser removal, shaving, and electrolysis. Most patients
prefer to not treat the area.
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