Vitiligo

Vitiligo is an acquired idiopathic disorder showing white non-scaly macules. The association with thyroid disease, pernicious anaemia and Addison’s disease suggests an autoimmune aetiology in some cases. About 30% of patients give a family history of the disorder. Melanocytes are absent from affected skin on histology.

Clinical presentation

Vitiligo affects 0.5% of the population, is seen in all races and is most troublesome in those with a dark skin. The sex incidence is equal, and the onset, usually between 10 and 30 years of age, may be precipitated by injury or sunburn. The sharply defined white macules are often symmetrical (Fig. 1). The hands, wrists, knees, neck and areas around orifices (e.g. the mouth) are frequently affected. Occasionally, vitiligo is segmental (e.g. down an arm), generalized or universal. The course is unpredictable; areas may remain static, spread or (infrequently) repigment. In light-skinned individuals, vitiligo may be discernible only in summer, when the non-vitiliginous areas become sun-tanned.

Fig. 1 Vitiligo showing symmetrical involvement of the forearms in a patient with pigmented skin.

Albinism

Albinism is an autosomal recessive condition in which the melanocytes fail to synthesize pigment in the epidermis, hair bulb and eye.

There are several syndromes of albinism. All are autosomal recessive and show a lack of pigment in the skin, hair, iris and retina. Melanocyte numbers are normal, but melanosome production fails due to defective gene control of tyrosinase (p. 8).

Albinism is uncommon (the prevalence is 1/20 000), although the diagnosis is straightforward. The skin is white or pink, the hair white and pigmentation is lacking in the eye (Fig. 2). Albinos have poor sight, photophobia and nystagmus. ‘Tyrosinase-positive’ albinos may pigment slightly with age, so that black African skin becomes yellow and freckled. In the tropics, albinos risk premature skin photoageing and the early onset of skin tumours, especially squamous cell carcinomas.

Fig. 2 Albinism in a black African patient.

Strict sun avoidance from childhood is essential. Opaque clothing, a wide-brimmed hat and sunscreens are needed. Prenatal diagnosis is possible.

Phenylketonuria

Phenylketonuria is an autosomal recessive inborn error of metabolism. Phenylalanine hydroxylase, which converts phenylalanine into tyrosine, is deficient. Phenylalanine and metabolites accumulate and damage the developing neonatal brain. The prevalence is 1/10 000 births.

Phenylketonuria is detected after birth by routine screening tests. Untreated, mental retardation and choreoathetosis develop. Patients have fair hair and skin, due to impaired melanin synthesis. Atopic eczema is common. A low phenylalanine diet, given early, prevents neurological damage.

Freckles and lentigines

Freckles (ephelides) are small, light-brown macules, typically facial, which darken on sun exposure. Lentigines are also brown macules but are scattered and do not darken in the sun. Freckles have normal basal layer melanocyte numbers but increased melanin. Lentigines have an increased number of melanocytes.

Freckles are common, especially in red-haired children. Lentigines may develop in childhood but are more common in sun-exposed elderly skin. Freckles require no treatment. Lentigines respond to cryotherapy.

Melasma (chloasma)

Melasma is a patterned macular facial pigmentation occurring with pregnancy and in women on oral contraceptives. The pigmentation is symmetrical and often involves the forehead (Fig. 3). Pregnancy stimulates melanocytes generally, and also increases pigmentation of the nipples and lower abdomen and in existing melanocytic naevi. Melasma may improve spontaneously. Topical tretinoin, azelaic acid or hydroquinone can reduce pigmentation. Sunscreens and camouflage cosmetics can help.

Fig. 3 Melasma affecting the cheek and causing a cosmetic disability.

Peutz–Jeghers syndrome

Peutz–Jeghers syndrome is a rare autosomal dominant condition. Lentigines around the lips (Fig. 4), buccal mucosa and fingers are associated with small bowel polyps. The polyps may cause intussusception and rarely undergo malignant change.

Fig. 4 The Peutz–Jeghers syndrome showing perioral lentigines.

Addison’s disease

Addison’s disease is characterized by hypoadrenalism with pituitary overproduction of adrenocorticotrophic hormone (ACTH). The skin signs are due to excess ACTH, which stimulates melanogenesis. Pigmentation may be generalized or limited to the buccal mucosa (Fig. 5), palmar creases, scars, flexures or areas subjected to friction. Addisonian-like pigmentation is also seen in Cushing syndrome, hyperthyroidism and acromegaly.

Fig. 5 Addison’s disease, with hyperpigmentation of the gingival and labial mucosae.

Drug-induced pigmentation

Drug-induced pigmentation may be due to stimulation of melanogenesis or deposition of the drug in the skin, but the mechanism is often not well understood (Table 3, p. 86). Of the commonly used drugs, amiodarone, phenothiazines and minocycline not infrequently induce pigmentation.

Table 3 Drug-induced pigmentation