Chapter 5
The Skin
What is the hardest of all? That which you hold the most simple; seeing with your own eyes what is spread out before you.
Johann Wolfgang von Goethe (1749–1832)
General Considerations
The skin, which is the largest organ of the body, is one of the best indicators of general health. Even a person without medical training is capable of detecting changes in skin color and texture. The trained examiner can detect these changes and at the same time evaluate more subtle cutaneous signs of systemic disease.
Diseases of the skin are common. Approximately one third of the population in the United States has a disorder of the skin that warrants medical attention. Nearly 8% of all adult outpatient visits are related to dermatologic problems. Basal cell carcinomas and squamous cell carcinomas (i.e., nonmelanotic skin cancers [NMSCs]) are by far the most common malignancies that occur in the United States. One of every three new cancers is a skin cancer, and the vast majority are basal cell carcinomas. Approximately 80% of the new skin cancer cases are basal cell carcinoma, 16% are squamous cell carcinoma, and 4% are melanoma. Most of these cases occur on the head and neck, which is evidence of the importance of sun exposure as a causative stimulus. Squamous cell carcinoma, the second most common skin cancer after basal cell carcinoma, afflicts more than 200,000 Americans each year. Although in most of these patients the cancer is treated and cured, skin cancer still causes more than 5000 deaths a year.
Melanoma is responsible for most skin cancer deaths, although it accounts for less than 5% of all skin cancer cases; there were 70,230 new cases of melanoma in 2011: 40,010 in men and 30,220 in women. The incidence of malignant melanoma is rising at a rate faster than that of any other tumor; it has more than tripled among white persons between 1980 and 2011. Melanoma was responsible for 8790 total deaths in 2011: 5750 men and 3040 women. In 2011, the lifetime risk of developing melanoma (invasive and in situ) for all races was 2.76%; in white persons, the lifetime risk was 3.15%, and in African Americans, it was 0.11%. The incidence rates of melanoma have been increasing for the past 30 years. Since 1992, incidence rates among white individuals have increased by 2.8% per year in both men and women. The reasons for this are unclear, but excessive sun exposure is a major factor.
Early detection and treatment of malignant melanoma, as with most cancers, offers the best chance of a cure. Both basal cell carcinoma and squamous cell carcinoma have a better than 99% cure rate if detected and treated early. Among patients with a superficial melanoma (<0.76 mm in depth), the survival rate is more than 99%, whereas among those with a larger lesion (>3.64 mm in depth), the 5-year survival rate is only 42% because these cancers are more likely to spread to other parts of the body. The external nature of melanoma gives the examiner an opportunity to detect these small, curable lesions.
The most important function of the skin is to protect the body from the environment. The skin has evolved in humans to be a relatively impermeable surface layer that prevents the loss of water, protects against external hazards, and insulates against thermal changes. It is also actively involved in the production of vitamin D. The skin appears to have the lowest water permeability of any naturally produced membrane. Its barrier to invasion retards potentially noxious agents from entering the body and causing internal damage. This barrier protects against many physical stresses and prohibits the invasion of microorganisms. By observing patients with extensive skin problems, such as burns, clinicians can appreciate the importance of this organ.
Structure and Physiologic Characteristics
The three tissue layers of the skin, depicted in Figure 5-1, are as follows:
Figure 5–1 Cross section through the skin, illustrating the structures in the epidermis and subcutaneous tissues.
The epidermis is the thin, outermost layer of the skin. It is composed of several layers of keratocytes, or keratin-producing cells. Keratin is an insoluble protein that provides the skin with its protective properties. The stratum corneum is the outermost layer of the epidermis and serves as a major physical barrier. The stratum corneum is composed of keratinized cells, which appear as dry, flattened, anuclear, and adherent flakes. The basal cell layer is the deepest layer of the epidermis and is a single row of rapidly proliferating cells that slowly migrate upward, keratinize, and are ultimately shed from the stratum corneum. The process of maturation, keratinization, and shedding takes approximately 4 weeks. The cells of the basal layer are intermingled with melanocytes, which produce melanin. The number of melanocytes is approximately equal in all people. Differences in skin color are related to the amount and type of melanin produced, as well as to its dispersion in the skin.
Beneath the epidermis is the dermis, which is the dense connective tissue stroma forming the bulk of the skin. The dermis is bound to the overlying epidermis by fingerlike projections that project upward into the corresponding recesses of the epidermis. In the dermis, blood vessels branch and form a rich capillary bed in the dermal papillae. The deeper layers of the dermis also contain the hair follicles with their associated muscles and cutaneous glands. The dermis is supplied with sensory and autonomic nerve fibers. The sensory nerves end either as free endings or as special end organs that mediate pressure, touch, and temperature. The autonomic nerves supply the arrector pili muscles, blood vessels, and sweat glands.
The third layer of the skin is the subcutaneous tissue, which is composed largely of fatty connective tissue. This highly variable adipose layer is a thermal regulator, as well as a protection for the more superficial skin layers from bone prominences.
The sweat glands, hair follicles, and nails are termed skin appendages. The evaporation of water from the skin by the sweat glands provides a thermoregulatory mechanism for heat loss. Figure 5-2 illustrates the types of sweat glands.
Within the skin, there are 2 to 3 million small, coiled eccrine glands. The eccrine glands are distributed over the body surface and are particularly profuse on the forehead, axillae, palms, and soles. They are absent in the nail beds and in some mucosal surfaces. These glands are capable of producing more than 6 L of watery sweat in 1 day. The eccrine glands are controlled by the sympathetic nervous system.
The apocrine glands are larger than the eccrine glands. The apocrine glands are found in close association with hair follicles but tend to be much more limited in distribution than are the eccrine glands. The apocrine glands occur mostly in the axillae, the areolae, the pubis, and the perineum. They reach maturity only at puberty, secreting a milky, sticky substance. Apocrine glands are adrenergically mediated and appear to be stimulated by stress.
The sebaceous glands are also found surrounding hair follicles. The sebaceous glands are distributed over the entire body; the largest glands are found on the face and upper back. They are absent on the palms and soles. Their secretory product, sebum, is discharged directly into the lumen of the hair follicle, where it lubricates the hair shaft and spreads to the skin surface. Sebum consists of sebaceous cells and lipids. The production of sebum depends on gland size, which is directly influenced by androgen secretion.
Nails protect the tips of the fingers and toes against trauma. They are derived by keratinization of cells from the nail matrix, which is located at the proximal end of the nail plate. The nail plate consists of the nail root embedded in the posterior nail fold, a fixed middle portion, and a distal free edge. The whitish nail matrix of proliferating epithelial cells grows in a semilunar pattern. It extends outward past the posterior nail fold and is called the lunula. The structural relationships of the nail are shown in Figure 5-3.
A hair shaft is a keratinized structure that grows out of the hair follicle. Its lower end, called the hair matrix, consists of actively proliferating epithelial cells. The cells at this end of the follicle, along with those of the bone marrow and gut epithelium, are the most rapidly growing dividing cells in the human body. This is the reason that chemotherapy causes hair loss, along with anemia, nausea, and vomiting. Visible hair is present over the entire body surface except on the palms, soles, lips, eyelids, glans penis, and labia minora. In apparently hairless areas, the hair follicles are small, and the shafts produced are microscopic. Hair follicles show conspicuous morphologic and functional heterogeneity. Follicles and their developing shafts differ from location to location in shaft length, color, thickness, curl, and androgen sensitivity. Some follicles, those in the axilla and inguinal areas, are very sensitive to androgens, whereas others in the eyebrow are insensitive. The arrector pili muscles attach to the follicle below the opening of the sebaceous gland. Contraction of this muscle erects the hair and causes “goose bumps.” The structure of a hair follicle is shown in Figure 5-4.
Review of Specific Symptoms
The main symptoms of disease of the skin, hair, and nails are the following:
Rash or Skin Lesion
There are some important points to clarify when a patient is interviewed about a new rash or skin lesion. The specific time of onset and location of the rash or skin lesion are critical. A careful description of the first lesions and any changes is vital. The patient with a rash or skin lesion should be asked the following questions:
“Was the rash initially flat? Raised? Blistered?”
“Did the rash change in character with time?”
“Have there been new areas involved since the rash began?”
“Is the lesion tender or numb?”
“What makes the rash better? Worse?”
“Was the rash initiated by sunlight?”
“Is the rash aggravated by sunlight?”
“What kind of treatment have you tried?”
“Do you have any joint pains? Fever? Fatigue?”
“Does anyone near you have a similar rash?”
“Have you traveled recently?” If so, “To where?”
“Have you had any contact with anyone who has had a similar rash?”
“Is there a history of allergy?” If so, “What are your symptoms?”
Note whether the patient has used any medications that may have changed the nature of the skin disorder.
Inquire whether the patient uses any prescription medications or over-the-counter drugs. Ask specifically about aspirin and aspirin-containing products. Patients can suddenly develop a reaction to medications that they have taken for many years. Do not ignore a long-standing prescription. Has the patient had any recent injections or taken any new medications? Does the patient use “recreational” drugs? Ask the patient about the use of soaps, deodorants, cosmetics, and colognes. Has the patient changed any of these items recently?
A family history of similar skin disorders should be noted. The effect of heat, cold, and sunlight on the skin problem is important. Could there be any contributing factor, such as occupation, specific food allergies, alcohol, or menses? Is there a history of gardening or household repair work? Has there been any contact with animals recently? The interviewer should also remember to inquire about psychogenic factors that may contribute to a skin disorder.
Determine the patient’s occupation, if it is not already known. Ascertain avocational and recreational activities. This information is important even if the patient has been exposed to chemicals or similar agents for years. Manufacturers frequently change the basic constituents without notifying the consumer. It may also take years for a patient to become sensitized to a substance.
Changes in Skin Color
Patients may complain of a generalized change in skin color as the first manifestation of an illness. Cyanosis and jaundice are examples of this type of problem. Determine whether the patient is aware of any chronic disease that may be responsible for these changes. Localized skin color changes may be related to aging or to neoplastic changes. Certain medications can also be responsible for skin color changes. Inquire whether the patient is taking or has recently taken any medications.
Pruritus
Pruritus, or itching, may be a symptom of a generalized skin disorder or an internal illness. Ask any patient with pruritus the following questions:
“When did you first notice the itching?”
“Did the itching begin suddenly?”
“Is the itching associated with any rash or lesion on your body?”
“Are you taking any medications?”
“Has there been any change in the sweating or dryness of your skin?”
“Have you been told that you have a chronic illness?”
Diffuse pruritus is observed in biliary cirrhosis and in cancer, especially lymphoma. Pruritus in association with a diffuse rash may be dermatitis herpetiformis. Determine whether the pruritus has been associated with a change in perspiration or dryness of the skin because either of these conditions may be the cause of the pruritus.
Changes in Hair
Inquire whether there has been a loss of hair or an increase in hair. Ascertain any changes in distribution or texture. If there have been changes, ask the following questions:
“When did you first notice the changes?”
“Did the change occur suddenly?”
“Has the change been associated with itching? Fever? Recent stress?”
“Are you aware of any exposure to any toxins? Commercial hair compounds?”
Changes in diet and medications are frequently responsible for changes in hair patterns. Hypothyroidism is frequently associated with loss of the lateral third of the eyebrows. Vascular disease in the legs often causes hair loss on the legs. Alternatively, ovarian and adrenal tumors can cause an increase in body hair.
Changes in Nails
Changes in nails may include splitting, discoloration, ridging, thickening, or separation from the nail bed. Ask the patient the following questions:
“When did you first notice the nail changes?”
“Have you had any acute illness recently?”
“Do you have any chronic illness?”
“Have you been taking any medications?”
Fungal disease causes thickening of the nail. Clues to systemic disease may be found by close examination of the proximal nail fold, the lunula, the nail bed, the nail plate, and the hyponychium. Acute illnesses are associated with lines and ridges in the nail bed and nail. Medications and chemicals are notorious for causing nail changes.
General Suggestions
All patients should be asked whether there have been any changes in moles, birthmarks, or spots on the body. Determine any color changes, irregular growth, pain, scaling, or bleeding. Any recent growth of a flat, pigmented lesion is relevant information.
All patients should be asked whether there are any red, scaly, or crusted areas of skin that do not heal. Has the patient ever had skin cancer? If the patient has had skin cancer, further questioning regarding the body location, treatment, and description is appropriate.
Effect of Skin Disease on the Patient
Diseases of the skin play a profound role in the way the affected patient interacts socially. If located on visible skin surfaces, long-standing skin diseases may actually interfere with the emotional and psychological development of the individual. The attitude of a person toward self and others may be markedly affected. Loss of self-esteem is common. The adult with a skin disorder often faces limitation of sexual activity. This disruption of intimacy can foster or increase hostility and anxiety in the patient. Skin is a sensitive marker of an individual’s emotions. It is known that blushing can reflect embarrassment, sweating can indicate anxiety, and pallor or “goose bump” skin may be associated with fear.
Patients with rashes have always evoked feelings of revulsion. Rashes have been associated with impurity and evil. Even today, friends and family may reject the individual with a skin disease. Patients with skin that is red, oozing, discolored, or peeling are rejected not only by family members but perhaps even by their physicians. At other times, skin lesions cause others to stare at the patient, which causes further discomfort. Some skin disorders may be associated with such extreme physical or emotional pain that marked depression may result and, on occasion, lead to suicide.
Skin diseases are often treated palliatively. Because numerous skin disorders have no cure, many patients go through life helpless and frustrated, as do their physicians.
The role of anxiety as a natural stressor in producing rashes is frequently observed. Stress tends to worsen certain skin disorders, such as eczema. This creates a vicious cycle, because the rash then exacerbates the anxiety. Rashes are common symptoms and signs of psychosomatic disorders.
Clinicians should discuss these anxieties with the patient in an attempt to break the cycle. The interviewer who tries to elicit the patient’s feelings about the disease allows the patient to “open up.” The fears and fantasies can then be discussed. The examiner should also be comfortable in touching the patient for reassurance. This tends to improve the doctor-patient relationship because the patient has a lesser sense of isolation.
Physical Examination
The only equipment necessary for the examination of the skin is a penlight. The examination of the skin consists of only two steps:
The examination of the skin depends on inspection, but palpation of a skin lesion must also be performed. Although most skin lesions are not contagious, it is prudent to wear gloves to evaluate any skin lesion. This is especially true because of the prevalence of skin disease associated with human immunodeficiency virus (HIV) infection. Palpation of a lesion helps define its characteristics: texture, consistency, fluid, edema in the adjacent area, tenderness, and blanching.
The patient and the examiner must be comfortable during the examination of the skin. The lighting should be adjusted to produce the optimal illumination. Natural light is preferable. Even in the absence of complaints related to the skin, a careful examination of the skin must be performed on all patients because the skin may provide subtle clues of an underlying systemic illness. Examination of the skin may be performed as a separate system approach, or, preferably, the skin should be examined when the other parts of the body are evaluated.
General Principles
The examiner should be suspicious of any lesion that the patient describes as having increased in size or changed in color. The development of any new growth warrants attention.
When examining the skin, the clinician initially determines the general aspects of the skin: the color, moisture, turgor, and texture of the skin.
Any color changes, such as cyanosis, jaundice, or pigmentary abnormalities, should be noted.
Red vascular lesions may be either extravasated blood into the skin, known as petechiae or purpura, or malformed elements of the vascular tree, known as angiomas. When pressure is applied by a glass slide over an angioma, it blanches. This is a useful test to differentiate an angioma from petechiae, which do not change when pressure from a glass slide is applied.
Asymmetry means that half the lesion appears different from the other half. Border irregularity describes a scalloped or poorly circumscribed contour. The color variation refers to shades of tan and brown, black, and sometimes white, red, or blue. A diameter larger than 6 mm, which is the size of a pencil eraser, is considered a danger sign for melanoma. A lesion that is evolving needs always to be evaluated.
The clinician should remember this axiom in dermatology: “There are more errors made by not looking than by not knowing.”
Excessive moisture may be seen in normal individuals, or it may be associated with fevers, emotions, neoplastic diseases, or hyperthyroidism. Dryness is a normal aging change, but it may also be seen in myxedema, nephritis, and certain drug-induced states. Look for excoriations, which might indicate the presence of pruritus as a clue to an underlying systemic illness.
When palpating the skin, evaluate its turgor and texture. Tissue turgor provides a mechanism for estimating the patient’s general state of hydration. If the skin over the forehead is pulled up and released, it should promptly reassume its normal contour. In a patient with decreased hydration, this response is delayed.
It is often difficult for the inexperienced examiner to evaluate the texture of the skin because texture is a qualitative parameter. Softness has occasionally been likened to the texture of skin over a baby’s abdomen. “Soft”-textured skin is seen in secondary hypothyroidism, hypopituitarism, and eunuchoid states. “Hard”-textured skin is associated with scleroderma, myxedema, and amyloidosis. “Velvety” skin is associated with Ehlers-Danlos syndrome.
Examination with Patient Seated
When the patient is seated, examine the hair and the skin on the hands and upper extremities.
Inspect the Hair
The hair and scalp are evaluated for any lesions. Is alopecia or hirsutism present? Pay attention to the pattern of distribution and texture of hair over the body. In certain diseases, such as hypothyroidism, the hair becomes sparse and coarse. In contrast, patients with hyperthyroidism have hair that is very fine in texture. Loss of hair occurs in many conditions: anemia, heavy metal poisoning, hypopituitarism, and some nutritional disease states, such as pellagra. Increased hair patterns are seen in Cushing’s disease, Stein-Leventhal syndrome, and several neoplastic conditions, such as tumors of the adrenal glands and gonads.
Inspect the Nail Beds
Evaluation of the nails can provide important clues about diseases. The nails may be affected in many systemic and dermatologic conditions. Nail-bed changes are usually not pathognomonic for a specific disease. Disorders stemming from renal, hematopoietic, or hepatic conditions may be evident from the nails. The nails should be inspected for shape, size, color, brittleness, hemorrhages underneath, transverse lines or grooves in the nail or nail bed, and an increased white area of the nail bed. Figure 5-5 illustrates some typical nail changes associated with medical diseases.
Beau’s lines are transverse grooves or depressions parallel to the lunula. Any severe, systemic illness that disrupts nail growth can produce Beau’s lines. They are often associated with infections (typhus, acute rheumatic fever, malaria, acquired immune deficiency syndrome [AIDS]), nutritional disorders (protein deficiency, pellagra), circulatory problems (myocardial infarction, Raynaud’s disease), dysmetabolic states (diabetes, hypothyroidism, hypocalcemia), digestive diseases (diarrhea, enterocolitis, chronic pancreatitis, sprue), drugs (chemotherapy agents), operations, and alcoholism. Beau’s lines are caused by conditions that cause the nail to grow slowly or even cease to grow for short intervals. The point of arrested growth is seen as a transverse groove in the nail. These lines are most commonly seen in the thumbnails and toenails. Figure 5-6A shows a patient’s fingers with Beau’s lines on the nails. Figure 5-6B shows Beau’s lines in the toenails of a patient who underwent major surgery 5 months earlier.
On occasion, a white transverse line or band results from poisoning or an acute systemic illness. These lines, called Mees’ bands, are historically associated with chronic arsenic poisoning. They are also seen in patients with Hodgkin’s disease, congestive heart failure, leprosy, malaria, chemotherapy, carbon monoxide poisoning, and other systemic insults. These lines or bands are also parallel to the lunula. By measuring the width of the line and approximating nail growth at 1 mm per week, the examiner may be able to determine the duration of the antecedent acute illness. Figure 5-7 shows the fingernails of a patient who received chemotherapy several weeks earlier.
Lindsay’s nails are also called “half-and-half nails.” The proximal portion of the nail bed is whitish, whereas the distal part is red or pink. Chronic renal disease and azotemia are the commonly associated conditions with this type of nail abnormality. Figure 5-8 shows Lindsay’s nails secondary to chronic renal failure.
Terry’s nails are white nail beds to within 1 to 2 mm of the distal border of the nail. These nail findings are most commonly associated with hepatic failure, cirrhosis, hypoalbuminemia, chronic congestive heart failure, hyperthyroidism, malnutrition, and adult-onset diabetes mellitus. Figure 5-9 shows classic Terry’s nails.
Splinter hemorrhages are formed by extravasation of blood from longitudinal nail bed blood vessels into adjacent troughs. Splinter hemorrhages are very common. It has been estimated that up to 20% of all hospitalized patients have splinter hemorrhages. Their presence is most often related to local, light trauma, but these hemorrhages are commonly associated with systemic disease. Classically associated with subacute bacterial endocarditis, splinter hemorrhages may also be seen in leukemia, vasculitis, infection, rheumatoid arthritis, systemic lupus erythematosus, renal disease, liver disease, and diabetes mellitus, among other diseases. Splinter hemorrhages are depicted in Figure 5-10.
Is koilonychia present? Koilonychia, or “spoon nail,” is a dystrophic state in which the nail plate thins and a cuplike depression develops. Spoon nails are most commonly associated with iron-deficiency anemia but may be seen in association with thinning of the nail plate from any cause, including local irritants. Figure 5-11 shows a normal fingernail in comparison with koilonychia secondary to iron-deficiency anemia.
Inspect the Nails for Clubbing
The angle between the normal nail base and finger is approximately 160 degrees, and the nail bed is firm. The angle is referred to as Lovibond’s angle. When clubbing develops, this angle straightens out to greater than 180 degrees, and the nail bed, when palpated, becomes spongy or floating. As clubbing progresses, the base of the nail becomes swollen, and Lovibond’s angle greatly exceeds 180 degrees. The nail has a bullous shape with exaggerated longitudinal and horizontal curvatures. A fusiform enlargement of the distal digit may also occur. In Figure 5-12, a normal finger is compared with a finger with nail clubbing.
To examine for clubbing, the patient’s finger is placed on the pulp of the examiner’s thumbs, and the base of the nail bed is palpated by the examiner’s index fingers. If clubbing is present, the nail appears to float on the finger. Figure 5-13 illustrates the technique for assessing whether early clubbing is present.
Since Hippocrates first described digital clubbing in patients with empyema, digital clubbing has been associated with various underlying pulmonary, cardiovascular, neoplastic, infectious, hepatobiliary, mediastinal, endocrine, and gastrointestinal diseases. Clubbing of the nails is most commonly acquired but may be inherited as an autosomal dominant trait. When not inherited as a familial trait, clubbing is most commonly seen associated with congenital cyanotic heart disease, cystic fibrosis, mesothelioma of the pleura, and pulmonary neoplasms. The most common acquired pulmonary cause is bronchogenic carcinoma; it is mainly seen in non–small-cell cancer (54% of all cases), and not generally seen in small-cell lung cancer (<5% of cases). In a patient with chronic obstructive pulmonary disease who manifests clubbing, other causes, including bronchiectasis or bronchogenic carcinoma, should be sought. Clubbing is also found in suppurative lung disease: lung abscess, empyema, bronchiectasis, and cystic fibrosis. The initial manifestation of clubbing is a softening of the tissue over the proximal nail fold.
Inspect the Nails for Pitting
Pitting of the nails is commonly associated with psoriasis and psoriatic arthropathy. Involvement of the nail bed and nail matrix by psoriasis causes the nail plate to be thickened and pitted. Nail involvement occurs in approximately 50% of all patients with psoriasis. Multiple pits in the nail are produced by discrete psoriatic foci in the nail matrix. Minor degrees of pitting are also seen in persons with no other skin complaints. Pitting rarely occurs in toenails. Psoriatic nail pitting is shown in Figure 5-14; Figure 5-15 illustrates a cross section of pitting. Figure 5-16A shows psoriatic nail lesions in another patient. Notice the characteristically dystrophic nail changes caused by subungual hyperkeratosis. Figure 5-16B is a close-up of a typical nail with psoriatic changes.
Inspect the Skin of the Face and Neck
Evaluate the eyelids, forehead, ears, nose, and lips carefully. Evaluate the mucous membranes of the mouth and nose for ulceration, bleeding, or telangiectasis. Is the skin at the nasolabial fold and mouth normal?
Examination with Patient Lying Down
Inspect the Skin of the Chest, Abdomen, and Lower Extremities
Ask the patient to lie down so that you can complete the examination of the skin. Inspect the skin of the chest and abdomen. Pay particular attention to the skin of the inguinal and genital area. Inspect the pubic hair. Elevate the scrotum. Inspect the perineal area. Evaluate the pretibial areas for the presence of ulcerations or waxy deposits.
Examine the feet and soles carefully for any skin changes. Spread the toes to evaluate the webs between them thoroughly.
Ask the patient to roll onto the left side so that you may examine the skin on the back, gluteal, and perianal areas.
Description of Lesions
If a skin lesion is found, it should be classified as a primary or secondary lesion, and its shape and distribution should be described. Primary lesions arise from normal skin. They result from anatomic changes in the epidermis, dermis, or subcutaneous tissue. The primary lesion is the most characteristic lesion of the skin disorder. Secondary lesions result from changes in the primary lesion. They develop during the course of the cutaneous disease.
The first step in identifying a skin disorder is to characterize the appearance of the primary lesion. In the description of the skin lesion, the clinician should note whether the lesion is flat or raised and whether it is solid or contains fluid. A penlight is often useful to determine whether the lesion is slightly elevated. If a penlight is directed to one side of a lesion, a shadow forms according to the height of the lesion.
The location of the lesion on the body is important. Therefore the distribution of the eruption is crucial in making a diagnosis. It may be rewarding to inspect a patient’s clothing when contact dermatitis or pediculosis (infestation with lice) is suspected. On occasion, occupational exposure may leave traces of contamination with oils or other materials that may be visible on the clothing and help in the assessment.
The three specific criteria for a dermatologic diagnosis are based on morphologic characteristics, configuration, and distribution, morphologic characteristics being the most important. The purpose of the following section is to acquaint the reader with the morphologic features of the primary and secondary lesions and the vocabulary associated with them.
Primary and Secondary Lesions
To facilitate reading, the primary lesions are listed here with regard to being flat or elevated and solid or fluid filled (Figs. 5-17 to 5-20). There is no “standard” size of a primary lesion. The dimensions indicated are only approximate. The secondary lesions are grouped according to their occurrence below or above the plane of the skin (Figs. 5-21 and 5-22). Other important lesions are shown and described in Figure 5-23.
Figure 5–17
Figure 5–18
Figure 5–19
Figure 5–20
Figure 5–21
Figure 5–22
Figure 5–23
Configuration of Skin Lesions
It is not essential for the examiner to make a definitive diagnosis of all skin disease. A careful description of the lesion, the pattern of distribution, and the arrangement of the lesion often points to a group of related disease states with similar manifesting dermatologic signs (e.g., confluent macular rashes, bullous diseases, grouped vesicles, papular rashes on an erythematous base). For example, grouped urticarial lesions with a central depression are suggestive of insect bites. Figure 5-24 lists the terms used to describe the configurations of lesions.
Figure 5–24
Clinicopathologic Correlations
Skin disorders are frequently perplexing to the examiner. When an examiner sees a rash, the common thought is “Where do I begin?” All too often, the examiner may become frustrated and not even attempt to make a diagnosis. Dermatologic terms are complicated, and the names of dermatologic disorders may be intimidating. Often the descriptions of skin disorders in textbooks are more confusing than helpful.
There are more than 2500 separately named dermatologic diagnoses. Most of these diseases occur in low frequencies; only 10 to 15 common conditions constitute approximately 50% of all dermatologic diagnoses. If the 50 most common conditions were considered, a diagnosis could be rendered for more than 95% of all patients.
In approaching a skin lesion, the examiner must do the following:
First, identify the primary lesion.
Second, identify its distribution.
Third, identify any associated findings.
Skin diseases evolve and their manifestations change. A lesion may evolve from a blister to an erosion, from a vesicle to a pustule, or from a papule to a nodule or tumor.
There are many common skin disorders or lesions with which the examiner should be familiar. Illustrated in the figures in this chapter are examples of some of these conditions; these cross-sectional diagrams illustrate the locations of these abnormalities in the skin and the involvement of the various skin layers in the pathogenesis of the conditions. The text describes the primary lesions.
A common wart is a common, benign growth usually caused by an infection of an epidermal cell by the human papillomavirus (HPV). There are more than 100 types of HPV, and different types of the virus cause different types of warts. Most types of HPV cause relatively harmless conditions such as common warts, whereas others may cause serious disease such as cancer of the cervix. Wart viruses pass from person to person. Individuals can be infected by the virus indirectly by touching a towel or object used by someone who has the virus. Each person’s immune system responds differently to HPV, so not everyone who comes in contact with HPV will develop warts. Warts are firm nodules with rough, keratinous surfaces that range in size from pinhead to pea size and can coalesce to form an extensive bed. There is vacuolation of the epidermis with scaling and an upward growth of the dermal papilla. Figure 5-25 illustrates a cross section through a wart. Two examples of finger warts are pictured in Figure 5-26.
Warts can also occur on the soles of the feet (plantar verruca), where they have a distinctive appearance because of constant pressure. They are very painful owing to the constant pressure, which forces the keratinous material into the deeper tissue. An example of a plantar wart on the heel is shown in Figure 5-27A. Notice the keratotic lesion with a yellow center, within which are visible areas of multiple red to black dots that represent hemorrhage from the tips of the dermal papillae. Classically, there is interruption of the normal skin lines as well. Figure 5-27B shows the excised lesion. Notice the depth of the lesion when viewed horizontally. Because warts are in the epidermis, excision just to the level of the dermis is sufficient for complete removal with minimal to no scarring.
Figure 5–27 Plantar wart. A, Note the keratotic lesion with the yellow center and areas of hemorrhage within. B, After excision.
A squamous cell carcinoma is a malignant neoplasm of keratocytes in the epidermis and is locally invasive into the dermis. The tumor results in a scaling, crusting nodule or plaque that can ulcerate and bleed. Squamous cell carcinoma is a potentially dangerous lesion that can infiltrate the surrounding structures and metastasize to lymph nodes and other organs. The causes include ultraviolet radiation, x-radiation, polycyclic hydrocarbons (e.g., tar, mineral oils, pitch, and soot), mucosal diseases (e.g., lichen planus and Bowen’s disease), scars, chronic skin disorders, genetic diseases (e.g., albinism and xeroderma pigmentosum), and human papillomavirus. The tumor develops predominantly on areas of skin exposed to sunlight. The latency from carcinogenic exposure to the development of the tumor may be as long as 25 to 30 years. Two examples of squamous cell carcinoma of the skin are pictured in Figure 5-28. Notice that the lesions are ulcerated with firm, raised indurated margins. Figure 8-11 also shows a patient with a squamous cell carcinoma and a malignant melanoma of the ear lobule. A squamous cell carcinoma on the lip of another patient is pictured in Figure 5-29. Notice the round, centrally ulcerating tumor. Figure 5-30 illustrates a cross section through a squamous cell carcinoma.
Although squamous cell carcinomas are usually found in sun-exposed areas, the lesion pictured in Figure 5-31 is on the plantar aspect of the foot. A callus is also present under the head of the first metatarsal.
A basal cell carcinoma is a malignant neoplasm of the basal cells of the epidermis and is the most common skin malignancy. The epidermis is thickened, and the dermis may be invaded by the malignant basal cells. It may manifest as a lesion with a pearly, rolled, well-defined margin and a central ulcerated depression. Although sunlight is an important etiologic factor, basal cell carcinomas are almost always seen on the face and rarely in other sun-exposed areas. They are slow-growing tumors and rarely metastasize, in contrast to squamous cell carcinomas. They are locally invasive, and when located near the eye or nose, they may invade the cranial cavity. If ulceration, bleeding, and crusting occur, a rodent ulcer is said to be present. Any nonhealing lesion should be carefully evaluated for the possibility of a basal cell carcinoma. Figures 5-32 to 5-34 illustrate the typical features of a basal cell carcinoma.
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