White : Diseases of the Skin - Structural Disorders of the Skin and Disease of Subcutaneous Tissues

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Gary M. White & Neil H. Cox

Diseases of the Skin

22	Structural Disorders of the Skin and Disease of Subcutaneous Tissues

EPIDERMAL DISORDERS

Epidermal atrophy

Atrophy (thinning) of the epidermis occurs in numerous situations, but rarely in isolation. Causes include the following.

•	Aging—both chronologic and solar (in which it is associated with elastosis of the upper dermis) (Ch17).
•	Lichen sclerosus—with associated homogenization of papillary dermal collagen (see later).
•	Necrobiosis lipoidica—see Chapter 12.
•	Lupus erythematosus—discoid and subacute forms (Ch.13).
•	Poikilodermas—see Chapter 33.
•	Iatrogenic—due to use of topical steroids and following radiotherapy (both with associated changes in the dermis).
•	Localized lesions—porokeratosis..

Epidermal thickening

Epidermal thickening (histologically, and sometimes clinically, termed acanthosis) occurs in numerous conditions, most of which are discussed elsewhere. Again, there is often a dermal component as well. Exposure to sunlight causes purely epidermal proliferation, but this is not generally clinically detectable. Examples of epidermal thickening include the following.

•	Local thickening in dermatoses—for example psoriasis, keratodermas, acanthosis nigricans, diabetic finger pebbling, and any disorder where chronic rubbing or scratching of the skin is a feature (producing lichenification, see Ch.6).
•	Acanthosis in localized lesions—for example prurigo nodularis, dermatofibroma, corns, and callosities (see later).

Callosities, corns, and similar disorders

These arise due to pressure or other forms of chronic, low-grade damage. The most common types of corn are on the sole of the foot, where they may mimic plantar warts (Fig. 22.1), although they also occur between the toes (Fig.22.2).

Fig. 22.1 A plantar com that has been pared down. A central translucent nodule of keratin is characteristic and distinguishes thi disorder from a wart (verruca).

Figure 22.2 Soft corns. These occur between the toes due to pressure, in this case due to overriding of the adjacent toe. By contrast to a plantar corn (Fig. 22.1), they produce a macerated or even eroded nodule that may cause diagnostic confusion.

Callosities occur at other sites of chronic friction, such as those related to sitting posture on the dorsum of the foot (Fig.22.3), or ‘pickers' nodules', which are most commonly seen on the hands. Knuckle pads (Figs 22.4 and 22.5) are a variation of this habit pattern.

Figure 22.3 Callosity on the dorsum of the foot. These arise due to sitting with the legs crossed with each foot tucked under the opposite thigh, and have been termed crossed leg callosities. They may also occur more toward the middle of the foot in individuals who kneel and sit back on to their feet.

Figure 22.4 Knuckle pads. These are present to some degree in many people, but may be exaggerated by friction. If prominent, they may be confused with warts.

Figure 22.5 A large knuckle pad in a young patient with psychologic problems who had habitually chewed his hands over many years.