Chapter 5. Structure of Skin Lesions and Fundamentals of Clinical Diagnosis

“You see, but you do not observe”

—Holmes to Watson in “Scandal in Bohemia,” by Arthur Conan Doyle, 1892

The diagnosis and treatment of diseases that affect the skin rest on the physician's ability to use the language of dermatology, to recognize the primary and sequential lesions of the skin, and to recognize the various patterns in which they occur. In this chapter, we discuss a fundamental approach to the patient presenting with a skin problem. We introduce the technical vocabulary of dermatologic description, the “dermatology lexicon.” It is important to know and use this standard terminology, as it is the first step in generating a differential diagnosis. Once a lesion has been described as a pearly, flesh-colored, telangiectatic, ulcerated nodule, the experienced physician puts basal cell carcinoma at the top of the differential diagnosis. It is also important to use standard dermatologic terminology for consistency in clinical documentation, in research, and in communication with other physicians.

The process of examining and describing skin lesions may be likened to that of viewing a painting. First, one stands back and takes in the whole “canvas,” viewing the patient from a few feet away, at which distance an overall assessment of the patient's general and cutaneous health may be made. One may note such findings as skin color and turgor, presence of pallor or jaundice, degree of sun damage, and the overall number and location of lesions. Next, one looks more closely at the “trees” or “mountains” that make up the landscape, describing and categorizing the specific lesions on the patient. Finally, one may closely examine the details of the canvas, taking in the texture and brush-strokes, using magnification to see the borders of a nevus or compressing a lesion to see if it blanches. Just as a knowledgeable viewer of art may recognize a work of Georges Seurat by its tiny, dot-like brush strokes, an experienced observer of the skin can recognize a melanoma by its asymmetry, irregular borders, and multiple colors.

History

Dermatology is a visual specialty and some skin lesions may be diagnosed at a glance. Nonetheless, the history is important and in complex cases, such as the patient with rash and fever or the patient with generalized pruritus, history may be crucial. Dermatologists vary in whether they prefer to take a history prior to, during, or after performing a physical examination. In practice, many take a brief history, perform a physical examination, then undertake more detailed questioning based on the differential diagnosis that the examination suggests.

For the following reasons, it is often useful to at least briefly examine the patient before taking a lengthy history:

• Certain skin conditions, such as classic plaque-type psoriasis or molluscum contagiosum, for example, present with such distinctive morphologies that the diagnosis may be immediately obvious, rendering extensive history taking unnecessary.
• A patient's history may contain “red herrings,” which lead the physician away from, rather than toward, the correct diagnosis. Examination of the patient before taking a history may yield a more complete and unbiased differential diagnosis.
• In certain situations, such as the evaluation of alopecia, initial examination of the patient to determine what type of hair loss is present allows the physician to pursue a line of questions pertinent to that type of alopecia.

In taking a history from a patient presenting with a new skin complaint, the physician's primary goal is to establish a diagnosis, with a secondary goal of evaluating the patient as a candidate for therapy. In patients whose diagnosis is already established, the physician's goals are to reevaluate the original diagnosis, monitor disease progress and complications, and modify treatment accordingly.

Box 5-1 presents a suggested approach to obtaining the history in a patient presenting with a skin problem. Clearly, not all of the questions are necessary for every patient. The physician will need to tailor the history depending on whether the chief complaint is a growth or an eruption, a nail or hair disorder, or another condition, and whether it is a new problem or a follow-up visit for an ongoing condition.

Examination of the Dermatologic Patient

Scope of the Complete Cutaneous Examination

The complete cutaneous examination includes inspection of the entire skin surface, including often-overlooked areas such as the scalp, eyelids, ears, genitals, buttocks, perineal area, and interdigital spaces; the hair; the nails; and the mucus membranes of the mouth, eyes, anus, and genitals. In routine clinical practice, not all of these areas are examined unless there is a specific reason to do so, such as a history of melanoma or a particular localizing complaint. A guide to performing the physical examination of the patient presenting with a skin problem is presented in Box 5-2.

Advantages to Performing a Complete Cutaneous Examination

Although it is not always essential or practical to perform a complete skin examination, there are many advantages to doing so, especially for new patients and challenging cases:

• Identification of potentially harmful lesions (e.g., skin cancers) of which the patient is unaware; any patient with a history of skin cancer or a chief complaint of a “new growth” deserves a full skin examination.
• Identification of benign lesions (e.g., seborrheic keratoses, angiokeratomas) that the patient was concerned about but reluctant to mention, thereby enabling the physician to provide reassurance.
• Finding hidden clues to diagnosis (e.g., scabies lesions on the penis, psoriatic plaques on the buttocks, Wickham striae of lichen planus on the buccal mucosa, nail pitting in alopecia areata).
• Opportunity for patient education (e.g., lentigines are a sign of sun damage and suggest the need for improved sun protection).
• Opportunity to convey the physician's concern about the patient's skin health as a whole. Patients appreciate this and also regard the physician as thorough.

Barriers to Performing a Complete Skin Examination

Despite the advantages of performing a full cutaneous examination, numerous barriers exist that may prevent the dermatologist from performing such an evaluation for every patient. Understandably, patients may decline a full examination when their chief complaint is relatively minor or localized, such as a wart or acne. In other cases, patients may express resistance to disrobing for a full examination due to embarrassment, especially when the physician is of the opposite gender. Sometimes the physician is uncomfortable performing a complete skin examination with the concern that a patient may misinterpret the examination as improper. In many instances, time constraints and lack of personnel to serve as chaperones limit the ability to perform full skin examination.

Ideal Conditions for the Complete Skin Examination

A complete skin examination is most effective when performed under ideal conditions. It is most important to have excellent lighting, preferably bright, even light that simulates the solar spectrum. Without good lighting, subtle but important details may be missed. The patient should be fully undressed, wearing only a gown that is easily moved aside, with a sheet over the legs, if desired. Underwear, socks, and shoes should be removed, as should any makeup or eyeglasses. The examining table should be at a comfortable height, with a head that reclines, an extendable footrest, and gynecologic stirrups. The examining room should be at a comfortable temperature for the lightly dressed patient. It should contain a sink for hand washing and disinfecting hand foam, as patients are reassured by seeing their physician wash hands before the examination. If the patient and physician are of opposite genders, having a chaperone in the room can make the examination more comfortable for both.

Recommended Tools for the Complete Skin Examination

Although the physician's eyes and hands are the only essential tools for examination of the skin, the following are often useful and highly recommended:

• A magnifying tool such as a loupe, magnifying glass, and/or dermatoscope.
• A bright focused light such as a flashlight or penlight to sidelight lesions.
• Glass slides or a hand magnifier for diascopy.
• Alcohol pads to remove scale or surface oil.
• Gauze pads or tissues with water for removing makeup.
• Gloves to be used for examination when scabies or another highly infectious condition (secondary syphilis) is suspected, when examining mucus membranes, and vulvar and genital areas, and when performing any procedure.
• A ruler for measuring lesions.
• Number 15 and number 11 scalpel blades for scraping and incising lesions, respectively.
• A camera for photographic documentation.
• A Wood's lamp (365 nm) for highlighting subtle pigmentary changes.

Technique of the Dermatologic Physical Examination

Just as there is no one correct way to perform a general physical examination, each physician approaches the complete skin examination with his or her own style. A common thread to effective styles of skin examination is consistency in the order of examining different body areas to ensure that no areas are overlooked. One approach to the complete skin examination is presented here. First, observe the patient at a distance for general impressions (e.g., asymmetry due to a stroke, obesity, pallor, fatigue, jaundice). Next, examine the patient in a systematic way, usually from head to toe, uncovering one area at a time to preserve patient modesty. Move the patient (e.g., from sitting to lying) and the illumination as needed for the best view of each body area. Palpate growths to determine whether they are soft, fleshy, firm, tender, or fluid-filled. Use of the hands to stretch the skin is especially useful in diagnosis of basal cell carcinoma, in which stretching skin reveals a “pearly” quality often not seen on routine inspection. A magnifier worn on the head leaves both hands free for palpation of lesions. Certain lesions, such as porokeratosis, are best examined with side lighting that reveals depth and the details of borders. During the examination, patients often find it reassuring for the physician to name and demystify benign lesions as they are encountered.

Special examination techniques for hair disorders are discussed in Chapter 88; these include having the patient sit in a chair so that the entire scalp is easily examined, parting the patient's hair at the front and occiput, and gently tugging on hairs to determine the fraction of loose (telogen) hairs. Examination of the nails is discussed in Chapter 89.

After completing the examination, it is important to document the skin findings, including the type of lesions and their locations, either descriptively or on a body map. Careful documentation is particularly important for suspicious lesions that are to be biopsied, so that the exact location may be found and definitively treated at a later date. Instant or digital photography is a useful adjunct for documentation.

Siemens (1891–1969) wrote, “he who studies skin diseases and fails to study the lesion first will never learn dermatology.” His statement reinforces the notion that the primary skin lesion, or the evolution thereof, is the essential element on which clinical diagnosis rests. Joseph Jakob von Plenck's (1738–1807) and Robert Willan's (1757–1812) work in defining basic morphologic terminology have laid the foundation for the description and comparison of fundamental lesions, thereby facilitating characterization and recognition of skin disease as, Wolff and Johnson state, to read words, one must recognize letters; to read the skin, one must recognize the basic lesions. To understand a paragraph, one must know how words are put together; to arrive at a differential diagnosis, one must know what the basic lesions represent, how they evolve, and how they are arranged and distributed.

Variation and ambiguity in the morphologic terms generally accepted by the international dermatology community have engendered barriers to communication among physicians of all disciplines, including dermatologists. In dermatologic textbooks, the papule, for example, has been described as no greater than 1 cm in size, less than 0.5 cm, or ranging from the size of a pinhead to that of a split pea. Thus, in forming a mental image of a lesion or eruption after hearing its morphologic description, physicians sometimes remain irresolute. The mission of the Dermatology Lexicon Project has been to create a universally accepted and comprehensive glossary of descriptive terms to support research, medical informatics, and patient care. Morphologic definitions in this chapter parallel and amplify those of the Dermatology Lexicon Project. Table 5-1 contains a summary of the lesions discussed.

Raised Lesions

Papule

A papule is a solid, elevated lesion less than 0.5 cm in size in which a significant portion projects above the plane of the surrounding skin. Papules surmounted with scale are referred to as papulosquamous lesions. Sessile, pedunculated, dome-shaped, flat-topped, rough, smooth, filiform, mammillated, acuminate, and umbilicated constitute some common shapes and surfaces of papules. A clinical example is lichen planus (Fig. 5-1; see Chapter 26).

Plaque

A plaque is a solid plateau-like elevation that occupies a relatively large surface area in comparison with its height above the normal skin level and has a diameter larger than 0.5 cm. Plaques are further characterized by their size, shape, color, and surface change. A clinical example is psoriasis (Fig. 5-2; see Chapter 18).

Nodule

A nodule is a solid, round or ellipsoidal, palpable lesion that has a diameter larger than 0.5 cm. However, size is not the major consideration in the definition of nodule. Depth of involvement and/or substantive palpability, rather than diameter, differentiates a nodule from a large papule or plaque. Depending on the anatomic component(s) primarily involved, nodules are of five main types: (1) epidermal, (2) epidermal–dermal, (3) dermal, (4) dermal–subdermal, and (5) subcutaneous. Some additional features of a nodule that may help reveal a diagnosis include whether it is warm, hard, soft, fluctuant, movable, fixed, or painful. Similarly, different surfaces of nodules, such as smooth, keratotic, ulcerated, or fungating, also help direct diagnostic considerations. A clinical example of a nodule is nodular basal cell carcinoma (Fig. 5-3; see Chapter 115).

Tumor, also sometimes included under the heading of nodule, is a general term for any mass, benign or malignant. A gumma is, specifically, the granulomatous nodular lesion of tertiary syphilis.

Cyst

A cyst is an encapsulated cavity or sac lined with a true epithelium that contains fluid or semisolid material (cells and cell products such as keratin). Its spherical or oval shape results from the tendency of the contents to spread equally in all directions. Depending on the nature of the contents, cysts may be hard, doughy, or fluctuant. A clinical example is a cystic hidradenoma (Fig. 5-4; see Chapter 119).

Wheal

A wheal is a swelling of the skin that is characteristically evanescent, disappearing within hours. These lesions, also known as hives or urticaria, are the result of edema produced by the escape of plasma through vessel walls in the upper portion of the dermis. Wheals may be tiny papules or giant plaques, and they may take the form of various shapes (round, oval, serpiginous, or annular), often in the same patient. Borders of a wheal, although sharp, are not stable and in fact move from involved to adjacent uninvolved areas over a period of hours. The flare, or ring of pink erythema, of a wheal may be intense if superficial vessels are dilated. If the amount of edema is sufficient to compress superficial vessels, wheals may in fact be white in the center or around the periphery, producing a zone of pallor. With associated inflammatory disruption of the vessels walls, wheals may have a deeper red color, may be purpuric, and are more persistent. A clinical example is dermatographism (Fig. 5-5; see Chapter 38).

Angioedema is a deeper, edematous reaction that occurs in areas with very loose dermis and subcutaneous tissue such as the lip, eyelid, or scrotum. It may occur on the hands and feet as well, and result in grotesque deformity.

Scar

A scar arises from proliferation of fibrous tissue that replaces previously normal collagen after a wound or ulceration breaches the reticular dermis. Scars have a deeper pink to red color early on before becoming hypo- or hyperpigmented. In most scars, the epidermis is thinned and imparts a wrinkled appearance at the surface. Adnexal structures, such as hair follicles, normally present in the dermis are absent. Hypertrophic scars typically take the form of firm papules, plaques, or nodules. Keloid scars are also elevated. Unlike hypertrophic scars (see eFig. 5-5.1; see Chapter 66), keloids exceed, with web-like extensions, the area of initial wounding. Atrophic scars are thin depressed plaques.

Comedo

A comedo is a hair follicle infundibulum that is dilated and plugged by keratin and lipids. When the pilosebaceous unit is open to the surface of the skin with a visible keratinaceous plug, the lesion is referred to as an open comedo. The black color of the comedo is due to the oxidized sebaceous content of the infundibulum (“blackhead”). A closed infundibulum in which the follicular opening is unapparent accumulates whitish keratin and is called a closed comedo. A clinical example is comedonal acne (Fig. 5-6; see Chapter 80).

Horn

A horn is a hyperkeratotic conical mass of cornified cells arising over an abnormally differentiating epidermis. A clinical example is verruca vulgaris (see eFig. 5-6.1; see Chapter 196).

Calcinosis

Deposits of calcium in the dermis or subcutaneous tissue may be appreciated as hard, whitish nodules or plaques, with or without visible alteration of the skin's surface. A clinical example is cutaneous calcinosis in dermatomyositis (see eFig. 5-6.2; see Chapter 156).

Depressed Lesions

Erosion

An erosion is a moist, circumscribed, depressed lesion that results from loss of a portion or all of the viable epidermal or mucosal epithelium. The defect extending to the most superficial part of the dermis may result in pinpoint bleeding in a sieve-like fashion. Erosions may result from trauma, detachment of epidermal layers with maceration, rupture of vesicles or bullae, or epidermal necrosis, for example. Unless they become secondarily infected, erosions do not scar. A clinical example is toxic epidermal necrolysis (Fig. 5-7; see Chapter 40).

Ulcers

An ulcer is a defect in which the epidermis and at least the upper (papillary) dermis have been destroyed. Breach of the dermis and destruction of adnexal structures impede reepithelialization, and the defect heals with scarring. Borders of the ulcer may be rolled, undermined, punched out, jagged, or angular. The base may be clean, ragged, or necrotic. Discharge may be purulent, granular, or malodorous. Surrounding skin may be red, purple, pigmented, reticulated, indurated, sclerotic, or infarcted. A clinical example is pyoderma gangrenosum (Fig. 5-8; see Chapter 33).

Atrophy

Atrophy refers to a diminution in the size of a cell, tissue, organ, or part of the body. An atrophic epidermis is glossy, almost transparent, paper thin and wrinkled, and may not retain normal skin lines. Atrophy of the papillary or reticular dermal connective tissue manifests as a depression of the skin. Atrophy of the panniculus results in a more substantial depression of the skin. eFig. 5-8.1 shows aged skin of the arm in an elderly woman (see Chapter 109).

Poikiloderma

As a morphologic term, poikiloderma refers to the combination of atrophy, telangiectasia, and varied pigmentary changes (hyper- and hypo-) over an area of skin. This combination of features may give rise to a dappled appearance to the skin. A clinical example is chronic radiodermatitis (see eFig. 5-8.2).

Sinus

A sinus is a tract connecting deep suppurative cavities to each other or to the surface of the skin. A clinical example is hidradenitis suppurativa (see eFig. 5-8.3; see Chapter 85).

Striae

Striae are linear depressions of the skin that usually measure several centimeters in length and result from changes to the reticular collagen that occur with rapid stretching of the skin. A clinical example is striae distensae (see eFig. 5-8.4; see Chapter 108).

Burrow

A burrow is a wavy, threadlike tunnel through the outer portion of the epidermis excavated by a parasite. A clinical example is scabetic burrow (see eFig. 5-8.5; see Chapter 208).

Sclerosis

Sclerosis refers to a circumscribed or diffuse hardening or induration of the skin that results from dermal fibrosis. It is detected more easily by palpation, on which the skin may feel board-like, immobile, and difficult to pick up. A clinical example is morphea (see eFig. 5-8.6; see Chapter 64).

Flat and Macular Lesions

Macule

A macule is flat, even with the surface level of surrounding skin, and perceptible only as an area of color different from the surrounding skin or mucous membrane. Maculosquamous is a neologism invented to describe macules with fine nonpalpable scaling, which may become apparent only after light scraping and scratching.

Perhaps the most important additional feature of a lesion other than primary morphology is color. Lesional color, which is often the first visual assessment made, is reliably reproducible with particular types of pathologies, such as destruction of melanocytes, dilatation of dermal blood vessels, or inflammation of vessel walls with extravasation of red blood cells. As such, color provides meaningful insight into pathologic processes of the skin and facilitates clinical diagnosis. Pigmentary changes represent an important and common type of macular color change and may be described as hyperpigmented (as in postinflammatory hyperpigmentation), hypopigmented (as in tinea versicolor), or depigmented (as in vitiligo).

Table 5-2 describes characteristic colors that may be noted with inspection of altered skin. A clinical example is lentigo (Fig. 5-9; see Chapter 122).

Patch

A patch is similar to a macule; it is a flat area of skin or mucous membranes with a different color from its surrounding. However, a patch is larger than 0.5 cm, and it may have a fine, very thin scale. Clinical examples include vitiligo, where the term “patch” may be used to describe larger macules or a “patchy” configuration (Fig. 5-10; see Chapter 74), and also cutaneous T-cell lymphoma, where early lesions may be thin slightly scaly patches.

Erythema

Erythema represents the blanchable pink to red color of skin or mucous membrane that is due to dilatation of arteries and veins in the papillary and reticular dermis. It exists in different colors, and to dub a primary lesion as erythematous alone is incomplete. Describing erythema with the color it most closely resembles provides a meaningful clue to diagnosis. For example, violaceous erythema brings to mind a differential distinct from salmon pink-colored erythema, even if both types of erythema involve papules. A clinical example is dusky erythema, as may be seen in a fixed drug eruption (see eFig. 5-10.1; see Chapter 41).

Erythroderma

Erythroderma is a generalized deep redness of the skin involving more than 90% of the body surface within days to weeks. Type of scaling or desquamation, which follows establishment of the generalized erythema, noted is suggestive of the primary process (Table 5-3). A clinical example is Sézary syndrome (see eFig. 5-10.2; see Chapters 23 and 145).

Surface Change

Scale, Desquamation (Scaling)

A scale is flat plate or flake arising from the outermost layer of the stratum corneum. Groups of coherent cornified cells packed with filamentous proteins desquamate in scales imperceptibly from the skin's surface under normal circumstances on a regular basis as the epidermis is replaced completely every 27 days. When epidermal differentiation is disordered, accumulation and casting of stratum corneum become apparent as scale that ranges in size from fine dust-like particles to extensive parchment-like sheets. In some cases, scale is observed only after scratching the lesion, a phenomenon known as latent desquamation. Scaly lesions are often described as “hyperkeratotic,” a term that is used both clinically and histopathologically.

Not all scales are similar, and the expert dermatologist with a well-trained eye can obtain diagnostically useful information from close examinations of the type of scale present. Table 5-3 describes the types of scale one may encounter. A clinical example is psoriasis vulgaris (Fig. 5-11; see Chapter 18).

Hyperkeratosis

Leider and Rosenblum define hyperkeratosis as “excessive cornification.” Siemens states that “the stratum corneum may be thinned or thickened.” In the latter, thickening may consist of normal keratin (hyperkeratosis) or of an abnormal keratin in which the cellular nuclei are retained and are stainable (parakeratosis). Different types of hyperkeratosis can be discerned histopathologically, but in clinical parlance “hyperkeratosis” refers to an excessive or thickened stratum corneum, often but not always scaly.

Crusts (Encrusted Exudates)

Crusts are hardened deposits that result when serum, blood, or purulent exudate dries on the surface of the skin. The color of crust is a yellow-brown when formed from dried serous secretion; turbid yellowish-green when formed from purulent secretion; and reddish-black when formed from hemorrhagic secretion. Removal of the crust may reveal an underlying erosion or ulcer. A clinical example is impetigo (Fig. 5-12; see Chapter 176).

Excoriations

Excoriations (see eFig. 5-12.1) are surface excavations of epidermis that result from scratching.

Fissure

A fissure is a linear loss of continuity of the skin's surface or mucosa that results from excessive tension or decreased elasticity of the involved tissue. Fissures frequently occur on the palms and soles where the thick stratum corneum is least expandable. A clinical example is fissure on the palm associated with contact dermatitis (see eFig. 5-12.2; see Chapter 13).

Lichenification

Repeated rubbing of the skin may induce a reactive thickening of the epidermis, with changes in the collagen of the underlying superficial dermis. These changes produce a thickened skin with accentuated markings, which may resemble tree bark. A clinical example is lichen simplex chronicus (Fig. 5-13; see Chapter 15).

Keratoderma

Keratoderma is an excessive accumulation of scale (hyperkeratosis) that results in a yellowish thickening of the skin, usually on the palms or soles, that may be inherited (abnormal keratin formation) or acquired (mechanical stimulation). A clinical example is plantar keratoderma in psoriasis (see eFig. 5-13.1; see Chapter 18).

Eschar

The presence of an eschar implies tissue necrosis, infarction, deep burns, gangrene, or other ulcerating process. It is a circumscribed, adherent, hard, black crust on the surface of the skin that is moist initially, protein rich, and avascular. A clinical example is thermal burn (see eFig. 5-13.2; see Chapter 95).

Fluid-Filled Lesions

Vesicle and Bulla

A vesicle is a fluid-filled cavity or elevation smaller than or equal to 0.5 cm, whereas a bulla (blister) measures larger than 0.5 cm. The fluid in the cavity exerts equal pressure in all directions to give rise to a spherical shape. Because of their size, bullae are easily identifiable as tense or flaccid weepy blisters. Clear, serous, hemorrhagic, or pus-filled contents may be visualized when the cavity wall is thin and translucent enough. Vesicles and bullae arise from cleavage at various levels of the epidermis (intraepidermal) or of the dermal–epidermal interface (subepidermal). The amount of pressure required to collapse the lesion may help predict whether the bulla is intraepidermal or subepidermal. However, reliable differentiation requires histopathologic examination of the blister cavity edge.

A clinical example of vesicle is the blistering aspect of impetigo caused by toxin-producing staphylococci (Fig. 5-14A; see Chapter 177). A clinical example of bulla is a bullous pemphigoid (Fig. 5-14B; see Chapter 56).

Pustule

A pustule is a circumscribed, raised cavity in the epidermis or infundibulum containing pus. The purulent exudate, composed of leukocytes with or without cellular debris, may contain bacteria or may be sterile. Depending on its sterility, the exudate may be white, yellow, or greenish-yellow in color. Pustules may vary in size and, in certain situations, may coalesce to form “lakes” of pus. When associated with hair follicles, pustules may appear conical and contain a hair in the center. A clinical example is superficial pyoderma (Fig. 5-15; see Chapter 176).

Furuncle

A furuncle (see eFig. 5-15.1; see Chapter 176) is a deep necrotizing folliculitis with suppuration. It presents as an inflamed follicle-centered nodule usually greater than 1 cm with a central necrotic plug and an overlying pustule. Several furuncles may coalesce to form a carbuncle.

Abscess

An abscess (see eFig. 5-15.2; see Chapter 176) is a localized accumulation of purulent material so deep in the dermis or subcutaneous tissue that the pus is usually not visible on the surface of the skin. An abscess is a pink erythematous, warm, tender, fluctuant nodule.

Purpura/Vascular Lesions

Purpura

Extravasation of red blood from cutaneous vessels into skin or mucous membranes results in reddish-purple lesions included under the term purpura. The application of pressure with two glass slides or an unbreakable clear lens (diascopy) on a reddish-purple lesion is a simple and reliable method for differentiating redness due to vascular dilatation (erythema) from redness due to extravasated erythrocytes or erythrocyte products (purpura). If the redness is nonblanching under the pressure of the slide, the lesion is purpuric. As extravasated red blood cells decompose over time, the color of purpuric lesions change from bluish-red to yellowish-brown or green.

Petechiae are small, pinpoint purpuric macules. Ecchymoses are larger, bruise-like purpuric patches. These lesions correspond to a noninflammatory extravasation of blood. If a lesion is purpuric and palpable (“palpable purpura”), the suggestion of an inflammatory insult to the vessel wall as a cause of extravasation of blood and inflammatory cells exists. A clinical example is leukocytoclastic vasculitis (Fig. 5-16; see Chapter 163).

Telangiectasia

Telangiectasia (see eFig. 5-16.1; see Chapter 174) are persistent dilatations of small capillaries in the superficial dermis that are visible as fine, bright, nonpulsatile red lines or net-like patterns on the skin.

Infarct

An infarct is an area of cutaneous necrosis resulting from a bland or inflammatory occlusion of blood vessels in the skin. A cutaneous infarct presents as a tender, irregularly shaped dusky reddish-gray macule or firm plaque that is sometimes depressed slightly below the plane of the skin. A clinical example is cholesterol emboli (Fig. 5-17; see Chapter 173).

Once the type or types of lesions have been identified, one needs to describe their shape, arrangement, and pattern of distribution, all useful characteristics in morphologic diagnosis. For example, a single scaly plaque on a patient's trunk may have a broad differential diagnosis, but the same plaques symmetrically distributed on the elbows, knees, and umbilicus would be highly suggestive of psoriasis. The following descriptions of shapes and arrangements of skin lesions may be applied to single or multiple lesions. For example, a single lesion may be linear or multiple lesions may assume a linear pattern.

Shape or Configuration of Skin Lesions

• Annular (Fig. 5-18): Ring-shaped; implies that the edge of the lesion differs from the center, either by being raised, scaly, or differing in color (e.g., granuloma annulare, tinea corporis, erythema annulare centrifugum).
• Round/nummular/discoid (Fig. 5-19): Coin-shaped; usually a round to oval lesion with uniform morphology from the edges to the center (e.g., nummular eczema, plaque-type psoriasis, discoid lupus).
• Polycyclic (see eFig. 5-19.1): Formed from coalescing circles, rings, or incomplete rings (e.g., urticaria, subacute cutaneous lupus erythematosus).
• Arcuate (see eFig. 5-19.2): Arc-shaped; often a result of incomplete formation of an annular lesion (e.g., urticaria, subacute cutaneous lupus erythematosus).
• Linear (see eFig. 5-19.3): Resembling a straight line; often implies an external contactant or Koebner phenomenon has occurred in response to scratching; may apply to a single lesion (e.g., a scabies burrow, poison ivy dermatitis, or bleomycin pigmentation) or to the arrangement of multiple lesions (e.g., lichen nitidus or lichen planus).
• Reticular (Fig. 5-20): Net-like or lacy in appearance, with somewhat regularly spaced rings or partial rings and sparing of intervening skin (e.g., livedo reticularis, cutis marmorata).
• Serpiginous (Fig. 5-21): Serpentine or snake-like (e.g., cutaneous larva migrans, in which the larva migrates this way and that through the skin in a wandering pattern).
• Targetoid (see eFig. 5-21.1): Target-like, with at least three distinct zones (e.g., erythema multiforme).
• Whorled (Fig. 5-22): Like marble cake, with two distinct colors interspersed in a wavy pattern; usually seen in mosaic disorders in which cells of differing genotypes are interspersed (e.g., incontinentia pigmenti, hypomelanosis of Ito, linear and whorled nevoid hypermelanosis).

Arrangement of Multiple Lesions

• Grouped/herpetiform (Fig. 5-23): Lesions clustered together (e.g., classic example is herpes simplex virus 1 reactivation noted as grouped vesicles on an erythematous base; also seen with certain arthropod bites).
• Scattered (see eFig. 5-23.1): Irregularly distributed.

Distributions of Multiple Lesions

• Dermatomal/zosteriform: Unilateral and lying in the distribution of a single spinal afferent nerve root; the classic example is herpes zoster (see Chapter 194).
• Blaschkoid (Fig. 5-24): Following lines of skin cell migration during embryogenesis; generally longitudinally oriented on the limbs and circumferential on the trunk, but not perfectly linear (see also Section “Shape or Configuration of Skin Lesions”); described by Alfred Blaschko and implies a mosaic disorder (e.g., incontinentia pigmenti, inflammatory linear verrucous epidermal nevus).
• Lymphangitic: Lying along the distribution of a lymph vessel; implies an infectious agent that is spreading centrally from an acral site, usually a red streak along a limb due to a staphylococcal or streptococcal cellulitis.
• Sun exposed: Occurring in areas usually not covered by clothing, namely the face, dorsal hands, and a triangular area corresponding to the opening of a V-neck shirt on the upper chest (e.g., photodermatitis, subacute cutaneous lupus erythematosus, polymorphous light eruption, squamous cell carcinoma).
• Sun protected: Occurring in areas usually covered by one or more layers of clothing; usually a dermatosis that is improved by sun exposure (e.g., parapsoriasis, mycosis fungoides).
• Acral: Occurring in distal locations, such as on the hands, feet, wrists, and ankles (e.g., palmoplantar pustulosis, chilblains).
• Truncal: Occurring on the trunk or central body.
• Extensor: Occurring over the dorsal extremities, overlying the extensor muscles, knees, or elbows (e.g., psoriasis).
• Flexor: Overlying the flexor muscles of the extremities, the antecubital and popliteal fossae (e.g., atopic dermatitis).
• Intertriginous: Occurring in the skin folds, where two skin surfaces are in contact, namely the axillae, inguinal folds, inner thighs, inframammary skin, and under an abdominal pannus; often related to moisture and heat generated in these areas (e.g., candidiasis).
• Localized: Confined to a single body location (e.g., cellulitis).
• Generalized: Widespread. A generalized eruption consisting of inflammatory (red) lesions is called an exanthema (rash). A macular exanthema consists of macules, a papular exanthema of papules, a vesicular exanthema of vesicles, etc. (e.g., viral exanthems, drug eruption).
• Bilateral symmetric: Occurring with mirror-image symmetry on both sides of the body (e.g., vitiligo, plaque-type psoriasis).
• Universal: Involving the entire cutaneous surface (e.g., erythroderma, alopecia universalis).

Table 5-4 describes some clinically relevant maneuvers and morphologic signs that point to particular integumentary or systemic diseases.

As the late Thomas B. Fitzpatrick often said, “dermatologists are physicians who can diagnose a rash!” They may also be internists, surgeons, biochemists, or immunologists; but without competency in dermatologic diagnosis they cannot qualify as dermatologists. However, this skill is not specific to dermatologists. Any physician who makes the effort to study the skin and learn the dermatologic lexicon can develop a functional appreciation of the fundamentals of diagnosis. The advanced diagnostic eye can only be acquired by endlessly repeated encounters in which the physician is forced not only to look at, but also to observe, the rash while an experienced mentor points the way. The most common error in dermatologic diagnosis is to regard the lesions as nonspecific “rashes” rather than as aggregates of specific individual lesions. As in surveying a blood smear, a “general impression” is not enough: The morphologic aspects of each individual cell must be carefully scrutinized and judged to be normal or abnormal. Too often, physicians adopt a speedy, superficial approach to the skin that they would not apply to any other organ that they examine (Table 5-5).

Lewis Thomas has said that “Medicine is no longer the laying on of hands, it is more like the reading of signals from machines.” In dermatology, there can be no replacement for the laying on of hands, and the physician is repeatedly gratified by reading signals not from machines, but from people.

Suggested Readings