DISORDERS OF PIGMENTATION :

HYPOPIGMENTATION
Vitiligo is a common disorder of depigmentation which probably has an autoimmune aetiology. Sufferers often have relatives with other organ-specific autoimmune disorders. It presents in childhood or early adult life with well-demarcated macules of complete pigment loss. There is no history of preceding inflammation. Patients are very susceptible to sunburn. Lesions are often symmetrical and frequently involve the face, hands (Fig. 23.37) and genitalia. The hair can also depigment. Trauma may induce new lesions. Spontaneous repigmentation can occur and often starts around hair follicles, giving a speckled appearance. However, repigmentation is rare if a lesion has persisted for more than 1 year or if the hair is depigmented. The psychological consequences of vitiligo can be devastating especially in Asian or black African people.

Treatment is very unsatisfactory and has no impact on the long-term outcome. Sunblocks should be used to prevent burning. Potent topical steroids or phototherapy help some individuals. Treatment with 0.1% tacrolimus ointment is currently under assessment, with conflicting early results. If vitiligo is almost universal and fixed, depigmentation with monobenzone may be considered. Finally, referral to a specialist camouflage clinic is often the most helpful 'treatment'.

Post-inflammatory hypopigmentation

This is one of the most common causes of pale skin. It is much more common in people with pigmented skin. It is seen as a consequence of eczema, acne or psoriasis and may even be the reason for individuals presenting to a doctor. Providing the skin disease is controlled, the pigmentation will recover slowly after many months. Post-inflammatory hyperpigmentation can also occur.

Oculocutaneous albinism

This is a group of rare autosomal recessive disorders affecting the pigmentation of skin, hair and eyes. It can affect all races. Melanocytes are in normal number but have abnormal function. Clinically it presents with universal pale skin, white or yellow hair and a pinkish iris. Photophobia, nystagmus and a squint are also present in most cases.

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Treatment involves obsessive protection against sunlight to avoid sunburning and development of skin cancer.

Idiopathic guttate hypomelanosis

This occurs most commonly in black African people and is of unknown aetiology. It presents with small (2-4 mm) asymptomatic porcelain-white macules, often on skin exposed to sunlight. The borders are often sharply defined and angular. There is no effective treatment.

Leprosy (see also p. 80)

Both tuberculoid leprosy and indeterminate leprosy can present with anaesthetic patches of depigmentation and should always be considered in people from endemic regions. Loss of hair and decreased sweating may also be present in the lesions.

HYPERPIGMENTATION

Freckles (ephelides)

These appear in childhood as small brown macules after sun exposure. They fade in the winter months.

Lentigos

These are a more permanent macule of pigmentation similar to freckles but they tend to persist in the winter. Solar lentigos (also called 'liver spots') occur in older people on exposed skin because of actinic damage.

Chloasma

These are brown macules often seen symmetrically over the cheeks and forehead and are most common in women. They can occur spontaneously but are also associated with pregnancy and the oral contraceptive pill.

Metabolic/endocrine effects

A generalized skin darkening can occur with chronic liver disease, especially haemochromatosis. It also is seen sometimes in Cushing's syndrome, Addison's disease (more marked in palmar creases and buccal mucosa) and Nelson's syndrome.

Peutz-Jeghers syndrome (p. 309)

This is an autosomal dominant genetic condition. It presents with brown macules of the lips and perioral region. It is associated with gastrointestinal polyposis which occasionally become malignant.

Urticaria pigmentosa (cutaneous mastocytosis)

This presents most commonly with multiple pigmented macules in children. These lesions tend to become red, itchy and urticated if they are rubbed (Darier's sign). Occasionally lesions may blister and in the rare congenital, diffuse form of the disease the skin can become thickened and leathery.

Occasionally, systemic symptoms are present, such as wheeze, flushing, syncope or diarrhoea, reflecting extensive mast cell degranulation from the skin. Anaphylaxis occurs very rarely and may be precipitated by mast cell degranulators such as aspirin or opiates. The condition spontaneously resolves after some years in children but is persistent in adults.

Skin biopsy shows an excess of mast cells in the skin. Recently a mutation in the proto-oncogene c-kit has been demonstrated, resulting in mast cell proliferation and mast cell apoptosis. Monoclonal antibodies against mast cell markers (tryptase and CD117) on immunohistochemistry confirm the diagnosis.

Treatment of the skin, if required, is with antihistamines or PUVA.

Rarely there may be infiltration of internal organs with mast cells (systemic mastocytosis), especially in adult disease or neonatal disease. This can involve any organ but especially the bone (where it can cause severe pain), gastrointestinal tract, liver and spleen. There is a small risk of developing leukaemia if the bone marrow is heavily infiltrated.

Other conditions with pigmentation

Café-au-lait macules are seen in neurofibromatosis types 1 and 2. They also occur in a wide variety of disorders including tuberous sclerosis, ataxia, telangiectasia, Fanconi's anaemia, multiple endocrine neoplasia type 1, McCune-Albright syndrome.

Multiple lentigines: apart from in Peutz-Jeghers syndrome these are also seen in xeroderma pigmentosum.

Acquired melanocytic naevi are seen in Turner's syndrome (p. 1064) and familial atypical mole-melanoma syndrome (dysplastic naevi, p. 1351).

FURTHER READING

Tharp MD et al. (2003) Mastocytosis. Advances in Dermatology 19: 207-236.