Hypertrichosis

Excerpt

Hypertrichosis is defined as excessive hair growth anywhere on the body in either males or females. It is important to distinguish hypertrichosis from hirsutism, which is a term reserved for females who grow an excessive amount of terminal hairs in androgen-dependent sites.

There are several ways of classifying hypertrichosis. These are based on the distribution (generalized vs. localized), the age of onset (congenital versus acquired), and the type of hair (vellus versus terminal).

Forms of generalized hypertrichosis include, but are not limited to, congenital generalized hypertrichosis (which is further divided into congenital hypertrichosis lanuginosa, universal hypertrichosis, and hypertrichosis universalis congenita), prepubertal hypertrichosis, acquired generalized hypertrichosis, and acquired hypertrichosis lanuginosa. They each differ in their etiology and clinical findings.

Forms of localized hypertrichosis include, but are not limited to, congenital localized hypertrichosis (congenital nevi, plexiform neurofibromas, Becker melanosis/nevus, nevoid hypertrichosis, spinal dysraphism, and the hair collar sign), localized hypertrichosis in hereditary and acquired systemic disease, and acquired localized hypertrichosis.

An understanding of lanugo, vellus, and terminal hair is integral in evaluating a patient with presumed hypertrichosis. Lanugo hair is fine, non-pigmented hair that covers the normal fetus. It is often several centimeters long. By the first few weeks of life, lanugo hair should be replaced by vellus hair on the body and terminal hair on the scalp. Vellus hair is lightly pigmented, fine, short hair, often referred to as “peach fuzz” that is found on the face, arms, stomach, and legs. Terminal hair is coarse, thick hair that is found on the scalp, underarms, and pubic area. In men, terminal hair is also found on the face. During puberty, vellus hair is replaced with terminal hair in androgen-dependent sites under the influence of testosterone.