Beckers nevus is a localized form of excessive hair growth

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Becker's Nevus

Hypertrichosis is an excessive hair growth disorder which involves only abnormal hair length and excessively high hair density as compared to normal growth in the racial, age and sex group of the patient. The hair growth in hypertrichosis is, with rare exceptions, not androgen related and the hair growth has no specific distribution.

Hypertrichosis is broadly classified as generalized and localized hypertrichosis. Each of these two categories is further categorized as congenital and acquired and results in a category of hypertrichosis known as localized acquired hypertrichosis.

Becker’s nevus is a type of localized acquired hypertrichosis. Becker’s nevus is a relatively common type of localized acquired hypertrichosis caused by physical injury. The disorder appears as a localized and irregular patch of hyperpigmention and hair growth, often after sun burn. Although it is an acquired hypertrichosis, there have been reports of very rare cases of congenital Becker’s nevus.

Becker’s nevus was first observed on the shoulders of two adolescents in 1949 who had suffered serious skin injury due to sun burn. The disorder usually affects the shoulders, anterior chest and the scapular regions. During puberty coarse black terminal hairs usually appear on the affected site.

According to some researchers, the disorder affects predominantly young men of whom adolescents are the majority, but rare cases of Becker’s nevus in childhood have also been reported. Rare cases of Becker’s nevus in middle age have also been noted. There are others who believe the disorder affects males and females equally. While it affects both males and females reporting by females is more, possibly because it is a rare case of androgen driven hypertrichosis where sufficient androgen is needed to develop the disorder. The early onset of the disorder in adolescence and male predominance does suggest an androgen mechanism of hair growth.

The disorder normally shows up as a solitary patch of pigmentation and hypertrichosis as large as the palm and sometimes as small as a nevu, but cases of multiple patches have also been reported. Initially the hyperpigmentation is presented first without the hypertrichosis. It is followed later by hypertrichosis which in some cases may take several years to appear. The actual area covered by hypertrichosis may not precisely coincide with the pigmented area and the pigmentation may disappear with time.

Histological examination shows that there is melanosis but no nevus cells. That is why many call the term Becker’s nevus, used to describe the disorder, a misnomer. Histological examination also showed that hair follicles are normal or enlarged. Electron microscopy shows that the changes are difficult to distinguish from UVB stimulated normal skin.

Smooth muscle involvement in Becker’s nevus

An increase in smooth muscle bundles has been observed in Becker’s nevus. In histological examinations the epidermis shows acanthosis with hyperpigmentation of the basal layer and a slightly increased number of melanocytes. The dermal part is mainly composed of several disorganized bundles of smooth muscle fibers that have no relation to hair follicles. These features show Becker’s to be harmatomatous rather than a melanocytic nevus.

The presence of smooth muscles and similar clinical presentations made it difficult to distinguish between “smooth muscle harmatoma” hypertrichosis and Becker’s nevus. This led some authors to speculate that “smooth muscle harmatoma” hypertrichosis, meaning “mass of tissues gone wrong”, and Becker’s nevus were variable presentations of the same underlying pathologic process. However, the presence of androgen receptors in the affected areas which are similar to androgen receptors in the genital skin and whose numbers are more than the receptors found in the unaffected surrounding areas does not support this view.

This, together with the fact of early onset of the disorder and the occasional presence of acne in the affected area lends further support to the view that Becker’s nevus is an androgen mediated disorder unlike smooth muscle harmatoma. Moreover, smooth muscle harmatoma is very often a congenital disorder containing vellus hairs as against terminal hairs in Becker’s nevus. Also there is relatively lighter pigmentation in smooth muscle harmatoma. Most importantly congenital smooth muscle harmatoma has not been reported to demonstrate an androgen dependent pattern of hypertrichosis like the Becker’s nevus.

There have been reports of Becker’s nevus associated, in mostly women patients, with hyperplasia of the ipsilateral breast, arm and shoulder girdle and hyperplasia of the ipsilateral leg. In males accessory scrotum has also been observed sometimes. There are also reports of some vertebral abnormalities, such as, scoliosis. A screen for associated bony and soft tissues abnormalities for patients with Becker’s nevus, particularly women, may be important. Most patients with Becker’s nevus are otherwise healthy.