The pigment of the skin is called melanin, which is made by the melanocytes
in the dermis of the skin. In this chapter, there will be a discussion of the major
pigmentation disorders of the skin. Pigment disorders of the skin involve
certain diseases that cause hypopigmentation such albinism (which involves a
decrease in skin pigmentation), depigmentation (which involves vitiligo, which
is the presence of patchy losses of pigment in the skin or albinism, which
affects the entirety of the skin and eyes), and hyperpigmentation (which can
be post-inflammatory or secondary to hormonal changes, such as is the case
in melasma). Technically, hypopigmentation means that the pigmentation
is decreased, while depigmentation involves a complete absence of
pigmentation, in which the skin is totally white.
INCIDENCE AND PREVALENCE OF
There are two main types of hyperpigmentation disorders encountered in a
dermatological practice. This includes melasma, of which the exact prevalence
is unknown, and post-inflammatory hyperpigmentation, which is focal
excesses of pigment after an injury or because of inflammation in the skin.
Melasma accounts for about 4-10 percent of dermatological visits and is
more common in post-pubertal women. It is extremely common in pregnancy,
with an incidence of about 25 percent per pregnancy.
The incidence of post-inflammatory hyperpigmentation occurs at a
different rate, depending on a person’s race. The incidence in AfricanAmericans
or people of African descent is about 9-10 percent, while the
incidence in Caucasians is about 1-2 percent. People of Chinese descent have
post-inflammatory hyperpigmentation at a rate of about 9-10 percent, while
Arabs have an incidence of about 8 percent. People of Latino descent have
about a 6-7 percent incidence of this disorder.
Vitiligo is fairly common and represents about 0.4 to 2 percent of the
population throughout the world. There is a slightly higher incidence in females,
with about half of all cases beginning in childhood. It is more obvious in people
who are darker-skinned but the incidence isn’t any higher in these individuals.
The incidence of albinism is also not related to race or ethnicity. About one
out of every 17,000 individuals will have one of the different types of albinism.
The most common type of albinism is oculocutaneous albinism (OCA), of which
about one in seventy people carry the recessive gene. The most prevalent
type of OCA is OCA2. There are four types of OCA, which vary in prevalence of
one in 3,900 individuals among African-Americans who have OCA2 to one in
85,000 people among individuals who have OCA4.
PREDISPOSING FACTORS FOR
The predisposing factors to melasma include being female and being
pregnant, indicating a hormonal influence to getting melasma. It is extremely
rare before puberty. There are main predisposing factors to having postinflammatory
hyperpigmentation include having darker skin, with an increase
in incidence among African-Americans and other darker-skinned ethnicities.
There are no specific predisposing factors to having vitiligo but, because it
is an autoimmune disease, it is more common among people who have other
autoimmune diseases. It is more noticeable in darker-skinned individuals but
having darker skin is not a predisposing factor to the disease.
Albinism has no predisposing factors and is found in all ethnicities. It is an
autosomal recessive depigmentation disorder and is a completely hereditary
disorder that is present at the time of birth.
SIGNS AND SYMPTOMS OF
There are no symptoms associated with post-inflammation hyperpigmentation or melasma. The major sign includes the presence of hyperpigmented areas of the body, which can be on the face with melasma or on any other part of the body with postinflammatory hyperpigmentation disorders. The major signs of vitiligo are the finding of depigmented or hypopigmented areas of the skin that are highly demarcated and symmetric, involving just a single spot, a couple of spots, or large segments of the body (in cases of segmental vitiligo).
CLINICAL PRESENTATION OF
The clinical presentation of melasma is the hyperpigmentation and discoloration of skin, usually on the face. There are three types of this disorder, including mandibular, malar
(on the cheeks), and centrofacial (in the middle of the face). The centrofacial kind is the most prevalent kind of melasma with mandibular melasma being the least prevalent. Rarely, other body parts are involved.
The clinical presence of post-inflammatory hyperpigmentation is the finding of increased pigmentation in areas of the body that have become inflamed from a wound or injury.
The area of increased pigmentation is more common in dark-skinned individuals and almost always is caused by a healed part of the skin that has either become injured or has been inflamed from a skin disease such as lichen planus or simple sunburn. The clinical presentation of vitiligo is the finding of highly-demarcated patches of hypopigmented or depigmented skin that may be on any body part, including the face, extremities, and trunk.
People with albinism may have hypopigmentation; however, the most striking presentation is that of an individual born with a complete absence of pigment on their entire body, accompanied by bright blue or gray eyes that lack any other pigmentation.
The pathology of all types of hypopigmentation and depigmentation will show a complete absence of melanocytes or the presence of melanocytes that cannot produce melanin because of an immune response or because of a genetic lack of the ability to make melanin.
TREATMENT AND MANAGEMENT OF
Melasma can be treated with topical cream drugs that bleach the skin, particularly those containing hydroquinone, which can be found over-thecounter. They will lighten the skin by bleaching it and are often combined with sunscreen to prevent the effects of the sun on bleached skin. Hydroquinone in concentrations of 2-6 percent, all of which can be effective in bleaching the skin to fade the areas of melasma. Avoidance of the sun helps and stopping drugs that contribute to melasma will decrease the areas of hyperpigmentation.
Patients with areas of hypopigmentation need strict protection against the sun. Those with OCA may need surgical treatment for strabismus. Careful evaluation on a regular basis for skin cancers needs to take place as these people will have an increased chance of sun-related skin cancers in the hypopigmented areas. Patients with vitiligo respond sometimes to topical corticosteroids and topically-applied calcipotriene. They also sometimes respond to PUVA therapy or psoralen plus ultraviolet A therapy. Topical calcineurin inhibitor therapy (pimecrolimus and tacrolimus) can be used for
facial or groin-related hypopigmentation.
COMPLICATIONS OF PIGMENT DISORDERS
There are no major complications of melasma, except for the fact that it can be socially-inhibiting and embarrassing. Patients with vitiligo and albinism are at a high risk for skin cancer because they can’t produce melanin to protect the skin from cancerous changes as a result of UV radiation exposure.
It is extremely rare to have universal vitiligo, which involves most of the body’s skin. The most common areas found to be depigmented include the face, nipples umbilicus, anal area, inguinal area, axillae, dorsal ankle surface, anterior shins, knees, elbows, dorsum of the hand, fingers and toes, and the flexor surface of the wrist. There are no symptoms of the disorder.
The signs of oculocutaneous albinism or OCA Type I involves having milky white hair and skin with bright blue or gray eyes. Type II disease involves pale skin but the presence of pigmented moles and lentigines that show up on sun-exposed skin with the possibility
of pigmented eyes. In type III albinism, the hair is red and the eye color is brown or blue with hypopigmentation of the skin. Type IV disease have signs similar
The main symptoms of OCA include light intolerance with regard to vision and skin that easily burns with exposure to sun. Patients tend to avoid the sunlight and may have more eye problems than just eye color changes, such as strabismus, decreased vision, loss of depth perception, and nystagmus.
ETIOLOGY OF PIGMENT DISORDERS
Nobody knows the exact etiology of melasma but it is believed to be possibly hormonal because it is more common in women and more common in women on hormone replacement therapy, birth control medications, and pregnancy. It appears to run in families and be more prominent after sun exposure.
The etiology of diffuse hyperpigmentation can be cancer (especially melanoma and lung cancers) or systemic diseases, such as hemochromatosis, Addison’s disease, and primary biliary cholangitis. A skin biopsy may be necessary to identify the etiology of the excess pigmentation since a simple skin examination may not point to an etiology.
Focal hypopigmentation can come from an autoimmune disorder (vitiligo) in which the immune system attacks the melanocytes. Post-inflammatory hypopigmentation and post-inflammatory hyperpigmentation both come from injuries to the skin, such as abrasions and burns. People who have atopic dermatitis, leprosy, kwashiorkor, tuberous scleroses, piebaldism (a genetic condition) or psoriasis can have focal pigmentation changes.
Chemical exposure to phenols and hydroquinone drugs can cause focal hypopigmentation of the skin.
The etiology of albinism is simply that this is an autosomal dominant or autosomal recessive condition that is extremely rare. Half of all patients have type II disease caused by mutations in the P gene, which stands for “pinkeyed gene”. No one knows exactly what causes the pink-eyed gene does but it is believed to be related to the pH of organelles in the melanocytes and the buildup of glutathione in the vacuoles in the melanocytes. Other genetic causes of albinism include malformations in genes that produce tyrosinase—
an enzyme that is necessary for the synthesis of melanin.
PATHOLOGICAL ASPECTS OF
The pathology of melasma can be identified by a skin biopsy. There is an epidermal melasma, dermal melasma, mixed melasma, and miscellaneous melasma, which is often seen by people with dark skin. The different types of melasma can only be identified by a skin biopsy, which may simply show an excess of melanin in the epidermis or the presence of macrophages that ingest melanin clustered in the dermis of the skin. In the mixed type, there is melanin both in the dermis and epidermis. In miscellaneous melasma, there are
simply more melanocytes in the skin.