There are many factors that alter the hue of a normal skin. The principal pigments are melanin and haemoglobin or its breakdown products. Carotene, if taken in large amounts in the diet, is concentrated in subcutaneous fat and in keratin, giving a yellow coloration to the skin. The skin can also change its colour by deposition of abnormal substances or by alteration of melanogenesis. These substances include drugs, bilirubin, haemosiderin, heavy metals and the deposition of metal salts, dyes and inlcs in tattooing. In practice, patients are most concerned with alterations in the degree of melanin pigmentation. This is especially so in those races who have a greater deposition of melanin in their skin as a normal characteristic. Alteration in the degree of pigmentation in those with pigmented skins may be striking and give rise to much personal and social stress.
Generalized hypopigmentation (albinism)
Albinism is inherited as an autosomal recessive disorder of melanin synthesis. This disorder produces a milky white skin, white hair, blue eyes and photophobia. There are different types, but in the commoner types there is a defect or inhibition of tyrosinase biosynthesis. In phenylketonuria (see p. 864) there is a failure to convert phenylalanine to tyrosine and hypopigmentation of the skin, hair and eyes -occurs.
Localized absence of melanocytes is seen in vitiligo. In postinflammatory hypopigmentation some melanocytes are seen but these have reduced activity. In pityriasis versicolor the lipophilic yeast Pityrosporum orbiculare produces substances that have an inhibiting effect on melanocytes. This condition can be treated with itraconazole. Industrial processes may expose the skin and melanocytes to substances, such as phenols, that are also toxic to the pigment-producing cells.
This is a common skin disease affecting approximately 1% of the population. It has a familial incidence. Melanocytes are lost from affected areas of skin. The reason is unclear but hypotheses include the following:
AUTODESTRUCTION OF MELANOCYTES by the products of melanin synthesis.
AUTOIMMUNE DAMAGE TO MELANOCYTES. Antigens have been detected on the surface of melanocytes and anti melanocyte antibodies have been detected in the sera of some patients. There is also an association of vitiligo with other diseases that demonstrate organspecific
antibody production, such as diabetes mellitus, thyroiditis and pernicious anaemia.
NEUROGENIC DYSFUNCTION has been invoked as an important factor in the production of rare naevoid patterns of the disease that tend to affect the limbs.
More than half the patients notice a loss of pigment before the age of 20 years. Areas of pigment loss are usually symmetrical and often annular in outline, though other shapes and patterns are seen. These areas tend to enlarge peripherally and present a convex edge to the normal pigmented skin. The initial areas of involvement often include the fingers, hands, face and genitalia. These regularly traumatized areas of skin may show evidence of the Koebner phenomenon (see p. 1000) when the disease is in an active phase. In endemic areas confusion may occur with leprosy and lead to social isolation.
This is unsatisfactory. Traditional therapy in places such as the Middle East includes the use of psoralens obtained from plant sources and applied topically or taken in tablet form. These substances enter into the skin and are then activated by sunlight. PUV A therapy used in the treatment of psoriasis is derived from these observations. Many treatments with PUV A therapy are required for vitiligo and there is concern over the long-term effects of the continuing use of high-intensity UV light for long periods, especially in younger patients. Potent topical corticosteroids, probably through their action as antiinflammatory agents, may induce repigmentation when applied to new lesions of vitiligo and a trial over a limited area of skin for a period of 6-8 weeks is warranted. There may be spontaneous recovery, especially in children. Pinch grafts of normal skin have been used but with active disease the Koebner effect involves donor sites.Postinflammatory
This may follow trauma to the skin from chemicals or physical agents or following inflammatory skin diseases. It is a noticeable feature in some patients with eczema. Mild hypopigmentation on the cheeks of children may be associated with scaling and erythema. Inflammatorychanges are usually seen in winter-time and are associated with conditions of low humidity and drying winds. The tanning of surrounding skin in summer will often make the eruption appear more striking, especially in dark-skinned children (pityriasis alba). Pityriasis versicolor may also tend to present in the summer for similar reasons.
The intensity of local inflammatory changes will be reduced with topical corticosteroids. Soap substitutes and emollients should be used when dryness of the skin is evident
Hyperpigmentation is most commonly seen following sun exposure but may also follow inflammatory changes in the skin. It is often much more evident in those races whose skins are already heavily pigmented. Epidermal naevi may contain an increased number of melanocyte and be pigmented. Melanin deposited in the dermis will often produce a blue discoloration of the skin, which is seen in the following:
• Mongolian blue spot on the backs of children, more especially those of Asian origin
• Naevus of Ito (on the neck)
• Naevus of Ota (on the face)
• Blue naevus
Brown-coloured naevoid lesions
IN NEUROFIBROMATOSIS, cafe-au-laitpatches and axillary freckling are seen.
ALBRIGHT’S SYNDROME produces extensive light brown discoloration of the skin over the trunk, buttocks and thighs that is often asymmetrical and affects children of preschool age.
XERODERMA PIGMENTOSUM is associated with a freckling type of hyper pigmentation on the face or other sunexposed sites. In those patients with severe disease it is associated with solar damage and cutaneous malignancy, which may be evident early in childhood.
FRECKLING on the skin of fair-skinned and otherwise normal persons increases with the length of sun exposure. Histological sections appropriately stained demonstrate an increase in the size and shape of melanosomes within the melanocyte.
These are circumscribed dark brown macules that are less than 0.5 cm in diameter. There is a localized increase in the number of melanocytes seen on light microscopy and the degree of pigmentation is often much more intense clinically than that seen with freckles. A generalized distribution of lentigines may be seen as part of a syndrome that includes cardiac defects (Leopard or Moynahan’s syndrome). In the Peutz-legher syndrome (orofacial lentiginosis) (see p. 213) lesions are localized to the face and hands and there is an association with intestinal
In haemochromatosis there is a grey/black component to the hyperpigmentation that is more evident in sunexposed areas of skin. Hypermelanosis may also be pronounced in patients with primary biliary cirrhosis. Endocrine disease
ADDISON’S DISEASE. Pigmentation may be diffuse but it is often much more pronounced on sun-exposed or traumatized skin, e.g. beneath bra straps or over the buccal mucosa in the mouth. Both adrenocorticotrophic hormone (ACTH) and melanocyte-stimulating hormone (MSH) are increased but ACTH plays the dominant role in producing the pigmentation.
HYPERTHYROIDISM may rarely produce a similar pattern of hyperpigmentation.
ACROMEGALY, CUSHING’S SYNDROME and ACTH therapy may also be associated with pigmentation that may be particularly pronounced in patients with sella turcica enlargement following adrenalectomy (Nelson’s syndrome), when multiple lentigines and oral hyperpigmentation are also seen.
PREGNANCY AND THE ORAL CONTRACEPTIVE PILL may both produce an increase in pigmentation on the neck, the areolae of the breasts, over the abdominal skin and genitalia. Involvement of the face (melasma) may cause the patient to seek medical advice.
NEOPLASTIC DISEASE AND CACHEXIA can produce a general darkening of the skin colour; more marked changes occur with ectopic ACTH production.
ACANTHOSIS NIGRICANS is most commonly seen as localized hyperpigmentation of the neck, axillae, groins or facial skin, but the changes may be generalized and profound. Velvety overgrowth of the skin at the flexures may be accompanied by filiform growths around the face, mouth or over the tongue, and by a curious roughness of the palmar or plantar skin (tripe palms). These changes are seen in middle-aged patients with visceral malignancies such as carcinoma of the stomach, but other types of neoplasia such as lymphomas have also been reported in association with these typical cutaneous features. Acanthosis nigricans can, however, occur without an underlying malignancy, with obesity in juveniles and together with endocrine diseases.
RENAL FAILURE is associated with hypermelanosis and an increase in MSH-like reactive hormone production is seen in some patients. A yellow/brown, widespread coloration of the skin often occurs; scaling and irritation may also be seen. The relief of itching is difficult to achieve
in such patients.
SYSTEMIC SCLEROSIS may produce localized pigmentary changes in sites such as the nape of the neck or over the shoulder girdle, but hyperpigmentation may be profound and generalized in some patients. Thickening of the skin is usually present and should offer a clue as to the primary diagnosis.
CHEMICAL DEPOSITION in the skin may occur as an occupational hazard, e.g. in those who process silver (argyria).
MERCURIALS may produce hypermelanosis, and gold when injected or taken by mouth may cause blue/black pigmentation, most evident on sun-exposed sites (chrysiasis) .
HAEMOSIDERIN, the iron-containing pigment, may also stimulate localized melanin production. This occurs on sites such as the legs of patients with varicose eczema following the loss of red cells into the skin. Mucocutaneous discoloration may also be seen with chronic lead poisoning.
Mepacrine imparts a yellow colour to the skin but the sclera are spared. Chloroquine and chlorpromazine may produce bluish-grey coloration of the skin, especially in areas exposed to the sun. Arsenicals ingested over a long interval cause macular hyperpigmentation together with areas of hypopigmentation (rain-drop appearance).