Injuries can cause localized or generalized hypertrichosis

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Injury Induced Hypertrichosis

Hypertrichosis is an excessive hair growth disorder characterized by abnormal hair length and density compared to normal growth of the racial, sex and age group of the patient. It does not have a specific hair distribution and is, with rare exceptions, not androgen driven.

Hypertrichosis has been classified as generalized and localized. In both these classes there is a class of hypertrichosis, which is injury induced.

Injury induced generalized hypertrichosis

Generalized hypertrichosis may be induced by a wide variety of underlying pathological states, brought about by physical injuries or insults.

People exposed to harmful chemicals such as hexachlorobenzene develop hepatic porphyria leading to hypertrichosis on the face and extremities. Severity of the hypertrichosis can be such that during an epidemic in Turkey, those affected were called monkey’s children.

General hypertrichosis is sometimes seen in patients with acrodynia, a rare reaction to chronic mercury exposure, causing erythema of fingers, toes and nose and painful hands and feet. The hypertrichosis disappears with the resolution of acrodynia

Head injuries and other cerebral disturbances may also cause generalized hypertrichosis. The drug phenytoin is used to treat patients with brain injury. It was earlier believed that phenytoin caused hypertrichosis in brain injury patients. Further observation showed that this kind of hypertrichosis occurred even in patients who were never treated with this drug. That is why some patients recover from this disorder when this drug is discontinued, whereas some do not.

Malnutrition, starvation and anorexia may also be causes of a generalized vellus hypertrichosis of the limbs and trunks in children and women who are dieting, particularly if there is an absence of carbohydrates in the diet. This type of hypertrichosis was seen in children during the Irish potato famine of the nineteenth century. Downy hypertrichosis of the trunk and arms is a very distinctive feature in some patients.

Malnutrition has also been cited as one of the reasons for the more generalized form of hypertrichosis seen in patients with AIDS, though there may be several other reasons. But the pathogenesis for such a development is not yet clear.

Infections such as tuberculosis can cause generalized hypertrichosis in children, the hair growth occurring mostly on the limbs and face and rarely on the rest of the body.

Injury induced localized hypertrichosis

Many types of physical injury can cause temporary localized hypertrichosis. These physical injuries include repeated trauma, local friction, irritation and inflammation involving the dermis regardless of whether there is any scarring. These injuries transform local vellus hairs to terminal hairs leading to localized hypertrichosis.

It is a common occurrence but is rarely reported particularly when it happens as an occupational hazard. An example usually cited of such an occupation related development is the localized hypertrichosis caused by friction and observed on the shoulders of some sack bearers and the necks of float bearers. Localized hypertrichosis also occurs on sites habitually bitten by mentally retarded patients. Frequent scratching of sites of insect bites also produces a localized hypertrichosis.

Local inflammations produced as a reaction to smallpox, tetanus and diphtheria vaccinations often become the sites of localized hypertrichosis.

Removal of orthopedic casts has often revealed vellus hypertrichosis on the limbs of patients. This is observed with casts made from plaster of Paris and fiberglass as well as in splints, which do not occlude the treated area. These observations have led to the hypothesis that hypertrichosis is caused by regional reasons related to the healing fracture and not by occlusion as is hypothesized by some. The hypertrichosis is usually temporary and the hair growth becomes normal with time.

Hypertrichosis in all the above cases are due to rubbing or friction and the common inciting factors seem to be local irritation and inflammation. This has led many to believe that hypertrichosis is caused by an increase in regional blood flow.

Becker’s nevus is a type of localized hypertrichosis first observed on two teenagers in 1949. The hypertrichosis was induced by severe skin injury due to sunburn. Initially local hyperpigmentation develops over the affected area followed later by hypertrichosis. Becker’s nevus generally appears as a single pigmented patch with hypertrichosis larger than the palm and occasionally as small as a nevu but multiple patches have also been reported. Such patches of localized hypertrichosis usually appear on the shoulders and affect young men. In the beginning, only pigmentation is present with hypertrichosis appearing later – in some cases after several years. Becker’ nevus affects mostly adolescents and males more than females but reporting by females is more. It is a rare case of androgen-stimulated hypertrichosis.