Colour and pigmentation

Before inspecting any rash or lesion, note the colour of the skin. Normal skin colour varies, depending on lifestyle and light exposure as well as constitutional and ethnic factors.

Pallor can have many causes. It may be:

temporary, due to shock, haemorrhage or intense emotion

persistent, due to anaemia or peripheral vasoconstriction.

Vasoconstriction is seen in patients with severe atopy – an inherited susceptibility to asthma, eczema and hay fever. Pallor is a feature of anaemia, but not all pale persons are anaemic; conjunctival and mucosal colour is a better indication of anaemia than skin colour. A pale skin resulting from diminished pigment occurs with hypopituitarism and hypogonadism.

Normal skin contains varying amounts of brown melanin pigment. Brown pigmentation due to deposited haemosiderin is always pathological. Albinism is an inherited generalized absence of pigment in the skin; a localized form is known as piebaldism. Patches of white and darkly pigmented skin (vitiligo) (Fig. 15.3) are due to a local and complete absence of melanocytes. Several autoimmune endocrine disorders are associated with vitiligo.

Figure 15.3 Vitiligo: a disorder of cutaneous pigmentation that is often autoimmune in origin and associated with other autoimmune disorders.

Abnormal redness of the skin (erythema) is seen after overheating, extreme exertion, sunburn and in febrile, exanthematous and inflammatory skin disease. Flushing is a striking redness, usually of the face and neck, which may be transient or persistent. Local redness may be due to telangiectasia, especially on the face. Cyanosis is a blue or purple-blue tint due to the presence of excessive reduced haemoglobin, either locally, as in impaired peripheral circulation, or generally, when oxygenation of the blood is defective. The skin colour in methaemoglobinaemia is more leaden than in ordinary cyanosis; it is caused by drugs, such as dapsone, and certain poisons.

Jaundice varies from the subicteric lemon-yellow tints seen in pernicious anaemia and acholuric jaundice to various shades of yellow, orange or dark olive-green in obstructive jaundice. Jaundice, which stains the conjunctivae, must be distinguished from the rare orange-yellow of carotenaemia, which does not. Slight degrees of jaundice cannot be seen in artificial light.

Increased pigmentation may be racial, due to sunburn or connected with various diseases. In Addison’s disease, there is a brown or dark-brown pigmentation affecting exposed parts and parts not normally pigmented, such as the axillae and the palmar creases; the lips and mouth may exhibit dark bluish-black areas. Note, however, that mucosal pigmentation is a normal finding in a substantial proportion of black patients.

More or less generalized pigmentation may also be seen in the following:

In pregnancy, there may be pigmentation of the nipples and areolae, of the linea alba and sometimes a mask-like pigmentation of the face (chloasma). Chloasma may also be induced by oral contraceptives containing oestrogen. A similar condition, melasma, may be seen in Asian and Afro-Carribean males.

Localized pigmentation may be seen in pellagra and in scars of various kinds, particularly those due to X-irradiation therapy. Venous hypertension in the legs is often associated with chronic purpura, leading to haemosiderin pigmentation. The mixture of punctate and fresh purpura and haemosiderin may produce a golden hue on the lower calves and shins. Pigmentation may also occur with chronic infestation by body lice. Erythema ab igne, a reticular pattern of pigmentation, can be seen in patients who use local heat to relieve chronic pain, or on the shins of people who habitually sit too near a fire. Livedo reticularis, a web-like pattern of reddish–blue discoloration mostly involving the legs, occurs in autoimmune vasculitis, especially in systemic lupus erythematosus (SLE) and antiphospholipid syndrome, when it is associated with cerebral infarction. The violet-coloured lesions of lichen planus are slightly raised, flat-topped papules (Fig. 15.4). Psoriasis usually presents as a symmetrical plaque on extensor surfaces (Fig. 15.5). Keloid consists of raised and inflammed, overgrown tender scar tissue (Fig. 15.6).

Figure 15.4 Flat-topped papules of lichen planus.

Figure 15.5 Salmon-pink plaque of psoriasis on elbow covered in characteristic silver scale.

Figure 15.6 Multiple keloid scarring of the back due to acne vulgaris. There is a genetic predisposition to the formation of keloid in scar tissue.

Skin lesions and eruptions

Skin eruptions and lesions should be examined with special reference to their morphology, distribution and arrangement. The terminology of skin lesions is summarized in Boxes 15.2 and 15.3. Colour, size, consistency, configuration, margination and surface characteristics should be noted.

Distribution of skin lesions

Consider the distribution of an eruption by looking at the whole skin surface:

Is it symmetrical or asymmetrical? Symmetry often implies an internal causation, whereas asymmetry may imply external factors.

Is the eruption centrifugal (radiating from the centre) or centripetal (radiating to the centre)? Certain common diseases such as chickenpox and pityriasis rosea are characteristically centripetal, whereas erythema multiforme and erythema nodosum are centrifugal. Smallpox, now eradicated, was also centrifugal.

A disease may exhibit a flexor or an extensor bias in its distribution: atopic eczema in childhood is characteristically flexor, whereas psoriasis in adults tends to be extensor.

Are only exposed areas affected, implicating sunlight or some other external causative factor?

If sunlight is suspected, are areas normally in shadow involved?

Are the genitalia involved?

Localized distributions may point immediately to an external contact as the cause, for example contact dermatitis from nickel earrings, lipstick dermatitis, etc.

Swelling of the eyelids is an important sign. Without redness and scaling, bilateral periorbital oedema may indicate acute nephritis, nephrosis or trichinosis. If there is irritation, contact dermatitis is the probable diagnosis. Dermatomyositis often produces swelling and heliotrope-coloured erythema of the eyelids without scaling of the skin. In Hansen’s disease (leprosy), the skin lesions may be depigmented or reddened, with a slightly raised edge; they are also anaesthetic to pinprick testing (Fig. 15.7) and mainly located in skin that is normally cooler than core body temperature.

Figure 15.7

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