Cyanosis

This is discussed on page 126. Melanin

The amount and distribution of melanin is modified in a number of situations (see Table 2.3).

Vitiligo and albinism may affect any race, whereas the characteristic pallor of hypopituitarism is only apparent in while races.

The overproduction of melanin in adrenal insufficiency results in the development of brown pigmentation of the skin, particularly in creases, in scars, overlying bony prominences and on areas exposed to pressure from belts, braces and tight clothing. Melanin may also be deposited in the mucous membranes of the lips and of the mouth, where it results in patches of slatcy grey-brown pigmentation (Fig. 2.38. p. 55). Pregnancy is commonly associated with a blotchy pigmentation of the face, 'melasma' or "chloasma", and increased pigmentation of the areolae, the linca alba and around the genitalia.

In both Addison's disease and hypopituitarism vasoconstriction occurs in the skin, so that pigmentation and pallor respectively are accentuated.

, ■■ /.:': ------- . .. ... ■ " ".. ■■—"'

TABLE 2.3 Local and generalised causes of abnormal melanin

production

Underproduction

Patchy (vitiligo)

Autoimmune loss ol melanocytes

Total absence (albinism)

Genetic failure to form tyrosinase

Partial absence (hypopituitarism)

Diminished pituitary formation ol

melanotrophic peptides

Overproduction

Adrenal Insufficiency

Excessive pituitary formation of

(Addison's disease)

meianotrophic peptides

Pregnancy

Owing to oestrogen, progesterone

and pituitary melanotrophic peptides

Heavy metals including iron

As in haemochromatosis

Freckles, lentigines and

Local overproduction

pigmented naevi

Hypercarotenaemia occasionally occurs in subjects who eat a lot of raw carrots and tomatoes. The orange-yellow pigment carotene is unevenly distributed in the subcutaneous fat and epidermis. It is seen particularly on the face, palms and soles but not in the sclerae. A yellowish discoloration of the face may appear in hypothyroidism because of impaired hepatic metabolism of carotene.

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