Pigmentation varies according to racial origin (skin types 1 to 6) and sun exposure. There are some important diseases that result in generalised or localised hyperpigmentation and hypopigmentation.
Naevi may result in hypopigmentation or hyperpigmentation and are discussed in module 8.
A Wood’s lamp may be useful as pigmentary changes are easier to identify while exposing to UV-A.
Generalised bronze hyperpigmentation may arise due to excessive circulating melanocyte stimulating hormone (MSH) and occurs in 95% of those with Addison’s disease, when it is more marked on pressure areas, in flexures, scars and buccal mucosa. It is associated with loss of pubic and axillary hair in women. Check early morning cortisol as a screening test.
Generalised bronze or greyish hyperpigmentation seen in 90% of those with haemochromatosis is also primarily due to melanin. It is more prominent on the genitals, in the flexures and on sun-exposed sites, particularly the face.
Generalised pigmentation can also rarely be a sign of metastatic melanoma.
Localised pigmentation may be due to:
Postinflammatory pigmentation follows injury (e.g. thermal burn) or inflammatory disorder (e.g. dermatitis) of the skin. It is mostly observed in darker skin types. Inflammation in the epidermis stimulates melanocytes to increase the synthesis of melanin and subsequently to transfer the pigment to surrounding keratinocytes. If the basal layer is injured (e.g. lichen planus), melanin pigment is released and subsequently trapped by macrophages in the papillary dermis (pigment incontinence). Dermal pigment tends to be a grey brown.
Postinflammatory pigmentation tends to become darker and more noticeable with sun exposure so sun protection and broad-spectrum sunscreens are an essential part of management. Although peeling agents may reduce epidermal pigmentation, nothing has been found useful to eradicate dermal melanosis.
Malassezia may induce enlarged melanosomes within basal melanocytes resulting in hyperpigmented pityriasis versicolor.
Phytophotodermatitis refers to a phototoxic reaction induced by UVA radiation on a furocoumarins (psoralens). The patient may present in spring or summer during the acute inflammatory stage, when there are linear blisters, or a few days to months later because of unsightly and bizarre pigmentation. The pigmentation is partly epidermal and partly dermal melanosis. Responsible plants include parsley, parsnips, celery, carrot, fig, lime and several species of wild flowers (umbelliferae).
Berloque dermatitis refers to bergapten (5-methoxypsoralens) phototoxicity. Bergapten is found in older fragrances (current regulations restrict the concentration of bergapten). The acute inflammatory dermatitis is sometimes unnoticed and the patient may present with streaky pigmentation on the neck. This is the same reaction as occurs after PUVA.
Melasma (chloasma) affects sun-exposed areas. It presents as symmetrical hyperpigmented macules on cheeks, upper lip, chin, and forehead. It affects adult women and they are often pregnant or taking some form of hormonal contraceptive.
Poikiloderma of Civatte is a characteristic weathering change affecting the lateral neck bilaterally, resulting in reticulate or follicular erythema, hyperpigmentation and atrophy. A similar disorder arising on the face is sometimes called erythrosis pigmentosa faciei, and is known as acquired brachial cutaneous dyschromatosis when it affects the arms
An SPF30+ sunscreen is essential if the pigmentation affects an exposed site. It is easier to lighten epidermal melanin than dermal melanin. These agents can be helpful:
Resurfacing using chemical peels, laser or dermabrasion may be effective but unfortunately risks further damage to the epidermis and formation of more pigment. Cautious cryotherapy to small areas of postinflammatory pigmentation can be effective but risks causing permanent hypopigmentation.
Cosmetic camouflage using make-up is sometimes the best advice.
Pigmented purpura is a term given to a group of disorders with underlying capillaritis. The cause of the inflammatory disorder affecting small blood vessels of the skin is rarely identified. Capillaritis can affect all races at any age. It results in irregular “cayenne pepper” coloured macules, papules, patches and plaques on the lower limbs or any body site. It may or may not itch.
Haemosiderin may also persist after vascular injury including varicose vein surgery and sclerotherapy. Haemosiderin deposition on the ankles is characteristic of venous disease and is often associated with atrophie blanche, lipdermatosclerosis, dermatitis and ulceration.
A congenital generalised reduction in pigmentation may be racial in origin or due to albinism. Pituitary failure resulting in lack of MSH rarely results in acquired hypomelanosis (pallor is much more frequently due to blood loss or anaemia).
When examining localised hypopigmentation, determine whether it is due to partial or complete loss of melanin (achromia or leukoderma).
The main diagnoses to consider are:
Pityriasis alba is a mild childhood form of eczema in which asymptomatic oval pink scaly plaques resolve to leave pale macules for some months or longer. Reduced numbers of active melanocytes and a decrease in number and size of melanosomes are seen in affected skin for unknown reasons.
Pityriasis versicolor may result in pale scaly plaques because malassezia induces tyrosinase inhibitors from the skin surface fatty acids.
Postinflammatory hypopigmentation may be macular, as occurs after cryotherapy, superficial burns or eczema, or due to dermal injury with scarring.
Vitiligo is considered an autoimmune disease but the precise pathogenesis remains conjectural. Vitiligo may be associated with other autoimmune diseases, especially thyroid disease and diabetes mellitus. Other associated autoimmune diseases include pernicious anaemia, Addison disease, and alopecia areata. It most often arises in adolescents and young adults, and is relatively common affecting about 1% of the population in all races.
The result is complete, or sometimes partial, depigmentation in affected areas because of loss of melanocytes. The white patches tend to be sharply circumscribed and are quite striking in darker skin, which can be cosmetically very disabling. They may at first be few in number but tend in somewhat erratic fashion to increase in time. They may koebnerise, i.e. arise in areas of injury such as sunburn or an operation scar.
Localized vitiligo is restricted to one general area including a segmental or quasi-dermatomal distribution.
It is important to advise careful sun protection, to minimise the difference between affected and unaffected skin and to prevent solar injury.
Response to therapy is highly variable. The following may help:
Depigmentation, using monobenzylether of hydroquinone may be considered in severely affected dark skinned individuals. Cosmetic camouflage using make-up, micropigmentation and tattooing may be very useful.