Skin, nails and hair

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:

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  Temporary, owing to shock, haemorrhage or intense emotion

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  Persistent, owing 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 owing 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. 20.3 ) are owing to a local and complete absence of melanocytes. Several autoimmune endocrine disorders are associated with vitiligo.

Abnormal redness of the skin (erythema) is seen after overheating, extreme exertion and sunburn and in febrile, exanthematous and inflammatory skin diseases. Flushing is a striking redness, usually of the face and neck, which may be transient or persistent. Local redness may be caused by telangiectasia, especially on the face. Cyanosis is a blue or purple-blue tint caused by 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 haemolytic 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, owing to sunburn or connected with various diseases. In Addison’s disease, a brown or dark-brown pigmentation affects 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:

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  Haemochromatosis, in which the skin has a peculiar greyish-bronze colour with a metallic sheen, owing to excessive melanin and iron pigment

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  Chronic arsenic poisoning, in which the skin is finely dappled affecting covered more than exposed parts

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  Argyria, in which the deposition of silver in the skin produces a diffuse slate-grey hue

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  The cachexia of advanced malignant disease

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-Caribbean males.

Localized pigmentation may be seen in pellagra and in scars of various kinds, particularly those owing 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 discolouration 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. 20.4 ). Psoriasis usually presents as a symmetrical plaque on extensor surfaces ( Fig. 20.5 ). Keloid consists of raised and inflamed, overgrown tender scar tissue ( Fig. 20.6 ). Dermatomyositis often produces swelling and heliotrope-coloured erythema of the eyelids without scaling of the skin.

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 20.4 and 20.5 . 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:

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

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  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.

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  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.

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

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

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  Are the genitalia involved?

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  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. 20.7 ) and mainly located in skin that is normally cooler than core body temperature.

The hair

Hair colour and texture are racial characteristics that are genetically determined. The yellow-brown Mongol race has black straight hair, negroid people have black curly hair and Caucasians have fair, brown, red or black hair. Secondary sexual hair begins to appear at puberty and has characteristic male and female patterns. Androgenic male pattern baldness is genetically determined, but requires adequate levels of circulating androgens for its expression. It occurs in women only in old age.

Growth of hair

Unlike other epithelial mitotic activity that is continuous throughout life, the growth of hair is cyclic ( Fig. 20.8 ), the hair follicle going through alternating phases of growth (anagen) and rest (telogen) . Anagen in the scalp lasts 3–5 years; telogen is much shorter, about 3 months. Catagen is the conversion stage from active to resting and it usually lasts a few days. The duration of the anagen phase determines the length to which hair in different body areas can grow. On the scalp, there are on average about 100 000 hairs. The normal scalp may shed as many as 100 hairs every day as a normal consequence of growth cycling. These proportions can be estimated by looking at plucked hairs (trichogram); the ‘root’ of a telogen hair is non-pigmented and visible as a white, club-like swelling. Normally 85% of scalp hairs are in anagen and 15% in telogen.