Diabetes mellitus

Candida albicans or bacterial infection is more common with untreated or poorly controlled diabetes. The neuropathy or arteriopathy of diabetes may result in ulcers on the feet (p. 73), and an associated secondary hyperlipidaemia can produce eruptive xanthomas (see Fig. 4). Diabetic dermopathy describes depressed pigmented scars on the shins, associated with diabetic microangiopathy. Necrobiosis lipoidica (Fig. 1), characterized by shiny atrophic yellowish–red plaques on the shins, was associated with diabetes in 65% of cases in one series, although others find a much lower figure. It affects less than 1% of all diabetics. Histologically, degenerate dermal collagen is seen with epithelioid cells and giant cells. The condition is chronic and may ulcerate. It is unresponsive to treatment. In contrast, granuloma annulare – recognized as palpable annular lesions on the hands, feet or face (Fig. 2) – is only rarely associated with diabetes and usually fades in 2 years. It must be differentiated from tinea corporis.

Fig. 1 Necrobiosis lipoidica.

Yellowish–red atrophic areas are seen on the shins of a diabetic patient.

Fig. 2 Granuloma annulare, seen on the dorsal aspects of the hands.

Thyroid disease

Both over- and underproduction of thyroxine result in skin and hair changes (see Table 1). Pretibial myxoedema (Fig. 3), seen in 1–10% of patients with hyperthyroidism, presents on the shins as raised erythematous plaques due to the deposition of mucin in the dermis. Topical steroids may be of benefit.

Fig. 3 Pretibial myxoedema.

The patient had been thyrotoxic.

Flushing

Flushing may be physiological, drug/food induced or associated with thyrotoxicosis, but rarely with carcinoid syndrome, mastocytosis and phaeochromocytoma.

Hyperlipidaemia

Both primary (genetic metabolic defects) and secondary (associated with diabetes, hypothyroidism or the nephrotic syndrome) lipid abnormalities may produce a variety of xanthomatous deposits. These may be:

Fig. 4 Eruptive xanthomas.

The patient had recently presented with diabetes mellitus.

Xanthelasma, seen as yellowish plaques on the eyelids, are not always due to a lipid abnormality. Treatment of xanthomas is usually aimed at underlying hyperlipidaemia.

Nutritional deficiency

Protein malnutrition results in retarded growth, wasted muscles, oedema and skin changes of altered pigmentation, desquamation and ulcers with, in black Africans, dry and pale-brown/red hair. Vitamin C deficiency (scurvy) and niacin deficiency (pellagra) produce distinct lesions. In Europe, scurvy is mainly seen in elderly men who do not eat fresh fruit or vegetables. Deficiencies of other B vitamins and of iron also produce cutaneous changes (Table 2). Acrodermatitis enteropathica is a rare inherited defect of zinc absorption seen in weaned infants and cured by zinc supplements.

Table 2 Skin signs of nutritional and internal disorders

Gastrointestinal disease

Malabsorption and its deficiency states have accompanying skin problems that include dryness, eczema, ichthyosis, pigmentation and defects of the hair and nails. Some gut disorders show specific skin changes (see Table 2). Coeliac disease is associated with an eczema (in addition to the link of dermatitis herpetiformis with gluten enteropathy, p. 79). and both Crohn’s disease and ulcerative colitis induce various eruptions. Peutz–Jeghers syndrome (p. 75) and pseudoxanthoma elasticum (p. 93) affect both the skin and the gut. Bowel bypass surgery induces a vesiculopustular eruption.

Other internal disorders

Hepatic and renal diseases often produce troublesome itching and pigmentation. Lesions may also be related to the underlying disease process, e.g. primary biliary cirrhosis (associated with systemic sclerosis) or vasculitis.

Sarcoidosis, a disorder of unknown aetiology in which granulomas commonly develop in the lung, lymph nodes, bone and nervous tissue, affects the skin in a third of cases. Cutaneous changes are variable and include brownish–red papules (typically on the face), nodules, plaques (on the limbs and shoulders, Fig. 5) and scar involvement. Lupus pernio is a particular pattern of sarcoidosis that appears as dusky-red infiltrated plaques on the nose or, occasionally, the fingers. Erythema nodosum may also result. Topical steroids have little effect. Resistant lesions may improve with intralesional steroid injection, but oral prednisolone or methotrexate is sometimes prescribed, particularly when there is progressive internal disease.

Fig. 5 Sarcoidosis.

Plum-coloured plaques are seen on the upper back.