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.
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).
Papule. Multiple, well-defined papules of varying sizes are seen. Flat tops and glistening surface are characteristic of lichen planus.
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).
Plaque. Well-demarcated pink plaques with a silvery scale representing psoriasis vulgaris.
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).
Nodule. A nodular basal cell carcinoma with well-defined, firm nodule with a glistening surface through which telangiectasia can be seen.
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.
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).
Cyst. A bluish colored resilient cyst filled with a mucous-like material on the cheek is cystic hidradenoma.
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).
Wheal. A sharply demarcated wheal with a surrounding erythematous flare occurring within seconds of the skin being stroked.
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.
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.
Scar. A pink firm hypertrophic scar.
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).
Comedo. Open and closed comedones on the face of this patient with acne.
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).
Horn. A conical column of hyperkeratosis overlying a pink papule. This cutaneous horn represents a verruca vulgaris.
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).
Calcinosis. Hard, whitish nodules on the chest representing dystrophic calcinosis in this patient with dermatomyositis.
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).
Erosion. Sloughing of the skin in this patient with toxic epidermal necrolysis leaves behind a large erosion.
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).
Ulcer. A large ulcer with a ragged base and heaped-up pink erythematous border on the leg representing progressing pyoderma gangrenosum.
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).
Atrophy. Thin, wrinkled atrophic skin that has lost its normal texture on the arm of this elderly woman.
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).
Poikiloderma. Poikiloderma with telangiectatic erythema, hyperpigmentation, hypo-pigmentation, and atrophy in chronic radiodermatitis.
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).
Sinus. Suppurative communicating fibrous sinus tracts in the groin representing hidradenitis suppurativa.
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).
Striae. Linear striae on the back of this woman who experienced a rapid growth spurt and weight gain.
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).
Burrows. Several, slightly scaling, thread-like burrows on the medial aspect of the palm, associated with a more generalized eczematous process in this patient infested with scabies mites.
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).
Sclerosis. Firm, slightly depressed sclerotic plaque on the leg of a girl with morphea. The surface is atrophic and there are areas of hypo- and hyperpigmentation.
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).
Macule. Uniform-colored brown macule with slightly irregular, sharply defined borders representing a lentigo on the lip.
Table 5-2 Implications of Color Changes in Altered Skin ||Download (.pdf)
Table 5-2 Implications of Color Changes in Altered Skin
Tuberculosis, sarcoidosis, leishmaniasis
Melanoma, purpura fulminans, calciphylaxis
Deep dermal pigment, reduced hemoglobin, tattoo, medication
Blue nevus, amiodarone
Melanin, hemosiderin, chronic inflammation, postinflammatory, dried serum
Inflammation with plasma cells
Deep hemosiderin, pyocyanin pigment, tissue eosinophilia
Pseudomonas infection, tattoo, Wells syndrome
Deep melanin or other pigment deposition
Chloroquine toxicity, Mongolian spot, erythema dyschromicum perstans
Inflammation, dilatation of deep dermal blood vessels
Borders of evolving morphea, dermatomyositis
Granulomatous inflammation with histiocytes having abundant cytoplasm
Epidermal proliferation without surface keratin
Basal cell carcinoma
Acute inflammation, dilatation of superficial dermal blood vessels, hemorrhage
Hemorrhage, acute inflammation, dilatation of blood vessels
Psoriasis, drug eruptions
Inflammation with involvement of epidermis, dilatation of blood vessels’ inflammation with edema
Pityriasis rubra pilaris, psoriasis, urticaria
Hemorrhage, deep hemosiderin, lichenoid inflammation
Lichen planus, Kaposi sarcoma
Reduced or absent melanin synthesis, postinflammatory
Tinea versicolor, albinism, vitiligo
Superficial Staphylococcus or Streptococcus infection mixed with keratinized cells, carotenoids, hemosiderin, bile pigment, accumulated lipid
Impetigo, xanthomas, sebaceous hyperplasia, necrobiosis lipoidica diabeticorum, jaundice
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.
Patch. Depigmented patches within areas of normal skin tone representing vitiligo.
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).
Erythema. A large area of dusky red erythema in the gluteal region representing a fixed drug eruption.
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).
Erythroderma. Generalized red erythema and exfoliative scale in this erythrodermic patient.
Table 5-3 Types of Scale ||Download (.pdf)
Table 5-3 Types of Scale
Type of Scale
Desquamation giving the appearance of dried, cracked skin.
Scales split of from the epidermis in finer scales or in sheets.
Scales appear as keratotic plugs, spines, or filaments.
Densely adherent scale with a sandpaper texture.
Scales are regular polygonal plates arranged in parallel rows or diamond patterns (fish-like, tesselated).
Scales appear as heaped-up column of scale.
Scales are thin large plates or shields attached in the middle and looser around the edges.
Scale is small and branny.
Psoriasiform (micaceous and ostraceous)
Scale is silvery and brittle and forms thin platelets in several loose sheets, like mica (micaceous scale). Large scales may accumulate in heaps, giving the appearance of an oyster shell (ostraceous scale).
Scales are thick, waxy or greasy, yellow-to-brown, flakes.
Scale appears as a lacy white pattern overlying violaceous flat-topped papules.
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).
Scale. Brittle silvery scales forming thin platelets in several loose sheets, like mica, on this plaque of psoriasis.
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).
Crust. Glistening, honey-colored, delicate crusts under the nose representing impetigo.
Excoriations (see eFig. 5-12.1) are surface excavations of epidermis that result from scratching.
Excoriation. Linear and punctate excoriations on the back induced by scratching.
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).
Fissure. A linear loss of continuity of the skin on the palm representing a fissure.
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).
Lichenification. An area of thickened skin with accentuated skin markings induced by repeated rubbing, representing lichenification noted in lichen simplex chronicus.
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).
Keratoderma. Yellowish thickening of skin on the soles in this patient with psoriasis.
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).
Eschar. Overlying eschars compromising peripheral perfusion in a burn victim.
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).
Vesicle (A) and bulla (B). Fragile subcorneal translucent vesicles representing impetigo caused by a toxin-producing Staphylococcus (A) and large tense subepidermal bullae filled with serous or hemorrhagic fluid in this patient with bullous pemphigoid (B).
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).
Pustule. Two pustules representing superficial pyoderma.
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.
Furuncle. An inflamed follicular-based nodule with a central necrotic plug that has come loose. There is crusting over the surface.
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.
Abscess. A tender red erythematous fluctuant abscess on the leg.
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).
Purpura. Nonblanching red erythematous papules and plaques (palpable purpura) on the legs, representing leukocytoclastic vasculitis.
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.
Telangiectasia. Blanching dilated superficial capillaries representing telangiectasia.
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).
Infarct. Dusky purple discoloration representing an area of infarction that eventuates in tissue necrosis. This patient had cholesterol emboli lodged in the distal end arteries of the toes.