Introduction
▶Recognizing and describing skin lesions accurately is essential to the diagnosis and differential diagnosis of skin disorders.
▶The first step is to identify the primary lesion, defined as the earliest lesion and the one most characteristic of the disease.
▶Next note the distribution, arrangement, and color of primary lesions, along with any secondary change (eg, crusting or scaling).
Types of Primary Lesions
■Macule: a small (<1 cm), circumscribed area of color change without elevation or depression of the skin (Figure 1.1)
■Patch: a larger (≥1 cm) area of color change without skin elevation or depression (Figure 1.2)
–Papules (<1 cm in diameter) (Figure 1.3)
–Nodules: lesion measuring 0.5 to 2.0 cm in diameter, most of which resides below the skin surface (Figure 1.4)
–Tumor: deeper than a nodule and measuring larger than 2 cm in diameter
–Wheals: pink, rounded, or flat-topped elevations due to edema in the skin (Figure 1.5)
–Plaques: plateau-shaped structures often formed by the coalescence of papules; larger than 1 cm in diameter (Figure 1.6)
–Vesicles: smaller than 1 cm in diameter and filled with serous or clear fluid (Figure 1.7)
–Bullae: 1 cm or larger in diameter and typically filled with serous or clear fluid (Figure 1.8)
–Pustules: smaller than 1 cm in diameter and filled with purulent material (Figure 1.9)
–Abscess: 1 cm or larger and filled with purulent material
–Cysts: 0.5 cm or larger in diameter; represent sacs containing fluid or semisolid material (unlike in bullae, the material within a cyst is not visible from the surface)
■Erosions: superficial loss of epidermis with a moist base (Figure 1.10)
■Ulcers: deeper lesions extending into the dermis or below (Figure 1.11)
Certain disorders are characterized by unique patterns of lesion distribution. For example,
▶Atopic dermatitis in children and adolescents typically involves the antecubital or popliteal fossae.
▶Seborrheic dermatitis in adolescents commonly involves not only the scalp but also the eyebrows and nasolabial folds.
▶Lesions of psoriasis are often seen in areas that are traumatized, such as the extensor surfaces of the elbows and knees.
▶Acne is limited to the face, back, shoulders, and chest, sites of the highest concentrations of pilosebaceous follicles.
The arrangement of lesions also may provide a clue to diagnosis. Some examples include
▶Linear: contact dermatitis due to plants (eg, poison ivy) (Figure 1.12), lichen striatus, and incontinentia pigmenti; may also occur in epidermal nevi, psoriasis, and warts
▶Grouped: herpes simplex virus infection (Figure 1.13), warts, molluscum contagiosum, microcystic lymphatic malformation
▶Dermatomal: herpes zoster (Figure 1.14)
▶Annular (ie, ring-shaped with central clearing): tinea corporis (Figure 1.15), granuloma annulare, erythema migrans, lupus erythematosus
Color
▶Erythematous: pink or red. When erythematous lesions are observed, it is important to note if they blanch. If the red cells are within vessels, as occurs in urticaria, compression of the skin forces the cells into deeper vessels and blanching occurs. However, if the cells are outside vessels, as occurs in forms of vasculitis, blanching will not occur. Non-blanching lesions are termed petechiae, purpura, or ecchymoses. Also note that in individuals with more deeply pigmented skin, erythema may be more difficult to appreciate.
▶Hyperpigmented: tan, brown, or black.
▶Hypopigmented: amount of pigment decreased but not entirely absent (as seen with postinflammatory pigmentary alteration).
▶Depigmented: all pigment absent (as occurs in vitiligo).
Alterations in the skin that may accompany primary lesions include
▶Excoriation: a superficial loss of skin (ie, an erosion) caused by scratching, picking, or rubbing.
▶Crusting: dried fluid; commonly seen following rupture of vesicles or bullae (as occurs with the “honey-colored” crust of impetigo).
▶Scaling: represents epidermal fragments that are characteristic of several disorders, including fungal infections (eg, tinea corporis) and psoriasis.
▶Atrophy: an area of surface depression due to absence of the epidermis, dermis, or subcutaneous fat; atrophic skin often is thin and wrinkled. Examples include steroid atrophy, morphea, and atrophoderma.
▶Lichenification: thickening of the skin from chronic rubbing or scratching (as occurs in atopic dermatitis); as a result, normal skin markings and creases appear more prominent (Figure 1.16).