What Should I Ask about the Present Illness?

What Does the Family History Add?

Why Is the Social History Important?

How Do I Describe What I See?

Recognizing and describing skin lesions accurately are essential to diagnosis. The first step is to identify the primary lesion, defined as the earliest lesion and the one most characteristic of the disease. Next, it is important to note the distribution, arrangement, and color of primary lesions, along with any secondary change, such as crusting or scaling.

What Are the Types of Primary Lesions?

Flat lesions include macules and patches. A macule is a small, circumscribed area of color change without elevation or depression, such as a café au lait macule. A patch is a large macule, although specific size criteria are lacking.

Elevated lesions may be solid or fluid filled. Solid lesions include papules (< 0.5 cm in diameter), nodules (≥ 0.5 cm in diameter), wheals (a pink, rounded or flat-topped elevation because of edema in the skin), and plaques (plateau-shaped structures often formed by the coalescence of papules). Elevated fluid-filled lesions may be vesicles (< 0.5 cm in diameter and filled with serous fluid), bullae (≥ 0.5 cm in diameter and filled with serous fluid), pustules (< 0.5 cm in diameter and filled with purulent material), and cysts (≥ 0.5 cm in diameter that represent sacs containing fluid or semisolid material).

Depressed lesions include erosions, which reflect superficial loss of epidermis with a moist base, or ulcers, deeper lesions extending into the dermis or below.

Why Is the Distribution of Lesions Important?

Certain disorders have unique patterns of distribution that can be useful for diagnosis. For example, seborrheic dermatitis commonly involves the scalp, eyebrows, and nasolabial folds. Psoriasis also affects the scalp, but lesions are often seen in areas that are traumatized, such as the elbows and knees. Acne is limited to the face, back, and chest, sites of the highest concentrations of pilosebaceous follicles.

How May Lesions Be Arranged?

How Do I Describe the Color of Skin Lesions?

Although the color of a lesion may be obvious, terms that may be helpful include

When erythematous lesions are observed, it is important to note if they blanch. If red blood cells are within vessels (e.g., 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; nonblanching lesions are termed petechiae, purpura, or ecchymoses.

What Are Secondary Changes?

Secondary changes are alterations in the skin that may accompany primary lesions and may be valuable in differential diagnosis.

How Do I Put It All Together?

Once you have identified the primary lesions, along with the distribution, arrangement, color, and secondary changes, your observations can be formulated into one or two sentences. For example, “Erythematous, scaling papules, and plaques are located on the extensor surfaces of the extremities. There is scaling of the scalp and pitting of the nails.” This description assists in differential diagnosis: By identifying scaling papules and plaques, you have placed the patient’s condition into the category of papulosquamous (elevated and scaling) diseases and have eliminated countless other disorders from consideration. In children, the most common papulosquamous disorders are chronic atopic or contact dermatitis, tinea corporis, and pityriasis rosea; less common causes are psoriasis, secondary syphilis, lichen planus, dermatomyositis, and lupus erythematosus. Given the location of the lesions on extensor surfaces and involvement of the scalp and nails, psoriasis becomes a primary consideration.

Tables 49-1 and 49-2 are provided to assist in differential diagnosis based on the morphology of lesions and list the disorders you are most likely to encounter, plus a few less common ones. When the physical findings are unclear, you will need a textbook or atlas of dermatology, a consultant, or another resource.

Table 49-1 Differential Diagnosis of Rashes in Neonates

Table 49-2 Differential Diagnosis of Rashes in Older Infants, Children, and Adolescents