Skin pigment changes have many causes

Originally published in The Ottawa Citizen October 3, 2004
Original title: Out, Out Damn Spot: Part 1

The formation of dark skin spots, or hyperpigmentation, can either be a benign condition or the development of a serious local or systemic disease.

In this two-part series, we will look at the causes and types of hyperpigmented skin changes.

Our skin contains pigment cells called melanocytes. These cells contain a tiny organ, the melanosome, which produces a pigment (melanin). Interestingly, the concentration of melanocytes in the skin of all races is the same. The skin colour is proportional to the number and size of melanosomes within each melanocyte.

Hormonal effects and skin irritation can increase the number of melanosomes within the cell, leading to darker skin. Sun exposure and certain diseases will increase the number of melanocytes, resulting in tanning or localized dark skin patches.

The diagnosis of these colour changes depends on three mechanisms: an increase in pigment cell numbers, an increase in melanin, or the laying down of another substance that darkens the skin.

A detailed history and physical exam will offer clues. Your doctor will want to know when the pigment changes started. Was it a birthmark? Did it develop during pregnancy or during childhood? Are there other physical symptoms and/or existing illnesses? Is the patient taking medications, herbal preparations or supplements? Has there been any recent exposure to new plants or ultraviolet (UV) radiation? These and other questions such as the colour, number and size of lesions help make the diagnosis.

What are some of the common hyperpigmented skin conditions?

Cafe au lait spots appear mainly on the trunk with a smooth or irregular border and bear the colour of coffee with milk. These lesions can be congenital (develop during fetal growth) or appear during childhood. The size varies from two millimetres to four centimetres in infants, and to 30 centimetres in adults. They are caused by increased melanin production.

The significance of this lesion is that it may be a sign (but in itself is not diagnostic) of neurofibromatosis (the Elephant Man’s disease). Removal of the lesions is unnecessary unless it is for cosmetic concerns.

Certain disease states like hyperthyroidism, Addison’s disease or hemochromatosis can increase the production of melanin. The hormonal imbalances from the former two conditions stimulate this effect. Although the pigment changes occur all over the body there seems to be a predilection for sun-exposed areas, the perineum (skin between the anus and genitals), armpits, areolas (dark skin around the nipple), palms and soles. Appropriate treatment will stop the pigment changes.

Seventy per cent of people with hemochromatosis, a disease that causes abnormally elevated blood iron levels, will develop a slate-grey skin colour change. It can stimulate an increase in melanin production that bronzes the skin. Treatment by phlebotomy (blood-letting) controls this disorder.

Ultraviolet light from the sun or tanning beds will also stimulate melanin production. However, some people may develop freckles (ephelides) about three millimetres in diameter on sun-exposed areas.

This is in contrast with tan- to dark-brown “mole-like” spots called lentigines that can appear all over the body. Lentigines measure about two to 20 millimetres and are not dependent on sun exposure. Both lentigines and freckles are benign and do not require any treatment.

Sunscreens and covering up in the sun will decrease the formation of more freckles. There are bleaching ointments and creams like hydroquinine to treat them. Some opt for laser therapy or peeling agents provided by a specialized treatment centre and physician.

Certain foods, medications and plants in combination with sun exposure can cause hyperpigmentation. Some of the plants and foods that cause these changes include carrot juice, fig leaves or stems, celery, dill, parsnips, lemons and limes.

These phototoxic reactions initially cause the skin to turn red, swell and blister in some people. Once this reaction calms, the melanocytes take over and overproduce pigment. Some medications can directly stimulate skin pigment production.

The descriptions and treatments of the hyperpigmented lesions are only to be used as a guide. Your doctor will be able to assess any additional implications of these conditions.

Next week: Part 2 will cover melanoma, diabetic skin changes and other common spots that seem to sprout as we age.

© Dr. Barry Dworkin 2004

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