8 Dermatology

Most of us think of our skin as a simple, durable covering for our skeleton, muscles, and internal organs. However, the skin is a complex organ, consisting of many parts and appendages (Fig. 8-1). The outermost layer, the stratum corneum, is an effective barrier to irritants, toxins, and organisms, as well as a membrane that holds in body fluids. The remainder of the epidermis manufactures this protective layer. Melanocytes within the epidermis help protect us from the harmful effects of ultraviolet light, and Langerhans cells are one of the body’s first lines of immunologic defense.

The dermis, consisting largely of fibroblasts and collagen, is a tough, leathery, mechanical barrier against cuts, bites, and bruises. Its collagenous matrix also provides structural support for a number of cutaneous appendages. Hair, which grows from follicles deep within the dermis, is important for cosmesis and protection from sunlight and particulate matter. Sebaceous glands are outgrowths of the hair follicles. Oil produced by these glands helps to lubricate the skin and contributes to the protective epidermal barrier. The nails are specialized organs of manipulation that also protect the sensitive digits. Thermoregulation of the skin is accomplished by eccrine sweat glands and changes in cutaneous blood flow, which is regulated by glomus cells. The skin also contains specialized receptors for heat, pain, touch, and pressure. Sensory input from these structures helps to protect the skin surface against environmental trauma. Beneath the dermis, in the subcutaneous tissue, fat acts as stored energy and as a soft, protective cushion.

Defects or alterations in any component of the skin may result in serious systemic disease or death. Each and every part of the skin can be affected by congenital, inflammatory, infectious, and degenerative disorders and tumors. For example, an altered stratum corneum is seen in ichthyosis; melanocytes are selectively destroyed in vitiligo; the epidermis proliferates in psoriasis; excess collagen is produced in the connective tissue nevus of tuberous sclerosis; hair is preferentially infested by certain fungi; and so on. In addition, the skin is affected by many systemic diseases and thus may provide visible markers for internal disorders. A skin examination may demonstrate lesions of vasculitis, explaining a child’s hematuria. The white macules of tuberous sclerosis may give insight into the cause of seizures.

Examination and Assessment of the Skin

The skin is the largest, most accessible, and most easily examined organ of the body and is the organ of most frequent concern to patients. Therefore, physicians should be able to recognize basic skin diseases and dermatologic clues to systemic disease.

Optimal examination of the skin is performed in a well-lit room. The physician should inspect the entire skin surface including hair, nails, scalp, and mucous membranes. This may be particularly problematic with infants and teenagers because it may be necessary to examine the skin in small segments to prevent cooling or embarrassment. Although no special equipment is required, a hand lens and side lighting aid in the assessment of skin texture and small, discrete lesions. A Wood’s lamp can improve precision in distinguishing hypopigmented from depigmented patches of skin.

Despite the myriad conditions affecting the skin, a systematic approach to the evaluation of a rash or exanthem assists and simplifies the process of developing a manageable differential diagnosis. After assessing the patient’s general health, the practitioner should obtain a detailed history of the skin symptoms including the date of onset, inciting factors, evolution of lesions, and presence or absence of pruritus and/or fever, as well as any other systemic symptoms. Recent immunizations, infections, drugs, and allergies may be directly related to new rashes. The family history may suggest a hereditary or contagious process, and the clinician may need to examine other members of the family. Review of nursery records and photographs helps to document the presence of congenital lesions. Attention should then turn to the distribution and pattern of the rash. The term distribution refers to the location of the skin findings, whereas the term pattern defines a specific anatomic or physiologic arrangement (e.g., the distribution of a rash may include the extremities, face, or trunk, and the pattern could be flexural or intertriginous). Identification of a pattern can assist in the development of a differential diagnosis even before the detailed morphology of the skin lesions is studied. Other common patterns include photodistributed (involving sun-exposed sites), acral (involving primarily the distal extremities), and dermatomal configurations (Fig. 8-2).

Next, the clinician should consider the local organization of the lesions, defining the relationship of primary and secondary lesions to one another in a given location. Are the lesions scattered or clustered? Are they linear, grouped, serpiginous, confluent, or discrete?

Last, the practitioner should identify the morphology of the cutaneous lesions. Primary lesions (macules, papules, pustules, wheals, plaques, vesicles, bullae, nodules, and tumors) arise de novo in the skin. Secondary lesions (erosions, ulcers, crusts, excoriations, fissures, lichenification, atrophy, and scars) evolve from primary lesions or result from the patient’s manipulation (e.g., scratching, picking, or popping) of primary lesions. Delineation of the primary and secondary lesions allows the clinician to develop a differential diagnosis on the basis of the anatomic level of the skin lesions (Table 8-1). Disorders restricted to the epidermis may be associated with macular color changes, such as in vascular telangiectasias, freckles, and vitiligo. In epidermal disorders, surface markings are commonly altered by scales, vesicles, pustules, crusts, and erosions. Bullous impetigo, atopic dermatitis, and ichthyosis are primarily epidermal disorders. When the dermis is also involved, lesions usually display distinct borders because of dermal inflammation and edema. Disorders with both epidermal and dermal changes include psoriasis, lichen planus, and erythema multiforme. Inflammatory disorders or tumors restricted to the dermis do not usually alter the surface markings. Lesional borders are distinct, and color changes and edema may be present. Examples of dermal disorders include granuloma annulare, intradermal nevi, urticaria, and hemangiomas. The diagnosis of subcutaneous disorders is made by careful palpation. The surface markings are normal, and the color of the skin may be normal or red. There is altered skin firmness, and tenderness may be present. Subcutaneous lesions include lipomas, deep hemangiomas, hematomas, subcutaneous fat necrosis, and erythema nodosum.

Table 8-1 Anatomic Depth of Lesions

Cutaneous Structure Physical Findings Specific Skin Disorders
Epidermis Altered surface markings Impetigo
Scale, vesicle, crust Café-au-lait spot
Color changes (black, brown, white) Atopic dermatitis
Epidermis and dermis Altered surface markings Psoriasis
Scale, vesicle, crust Atopic dermatitis
Distinct borders Contact dermatitis
Color changes (black, brown, white, and/or red) Cutaneous lupus erythematosus
Dermis Normal surface markings Urticaria
Color changes Granuloma annulare
Altered dermal firmness Hemangioma
  Blue nevus
Subcutaneous tissue Normal surface markings Hematoma
Normal or red skin color Cold panniculitis
Altered skin firmness Erythema nodosum

From Cohen BA: Pediatric dermatology, ed 2, London, 1999, Mosby.

Because an outline of specific pediatric dermatoses defies any one scheme of organization, this text follows a clinically practical format. First, this chapter covers common papulosquamous and vesiculopustular eruptions, which account for a majority of rashes seen in children. This is followed by sections covering reactive erythemas, insect bites and infestations, tumors and infiltrations of the skin, neonatal dermatology, vascular lesions, congenital and acquired nevi, and disorders of pigmentation. The chapter concludes with a discussion of disorders of the hair and nails and complications of topical therapy.

Papulosquamous Disorders

Papulosquamous eruptions share the morphologic features of papules and scales. However, the clinician must understand that the papulosquamous disorders, which are quite diverse, are produced by a variety of different mechanisms. In psoriasis, increased turnover of keratinocytes by the basal cell layer results in a markedly thickened epidermis and stratum corneum (scaly surface layer). In dermatitic processes such as atopic dermatitis, contact dermatitis, seborrheic dermatitis, pityriasis rosea, and fungal infections, inflammation results in increased production and abnormal maturation of epidermal cells, with subsequent scale production. Increased adherence of cells in the stratum corneum may result in the retention hyperkeratosis characteristic of ichthyosis vulgaris, which is frequently found in association with atopic dermatitis.


Psoriasis is a common disorder characterized by red, well-demarcated plaques covered with dry, thick, silvery scales. These tend to be located on the extensor surfaces of the extremities, the scalp, and the buttocks. In some patients, the distribution consists of large lesions over the pressure points of the knees and elbows (Fig. 8-3, AD). Thickening and fissuring of the skin of the palms may also be seen (Fig. 8-3, E). In some children, numerous droplike (guttate) lesions are found scattered over the body (Fig. 8-4), often after a bout of group A β-hemolytic streptococcal infection (which may have been recognized or have been subclinical). In infants, psoriasis may present as a persistent diaper dermatitis (see Fig. 8-45). Lesions of psoriasis are often induced at sites of local injury such as scratches, surgical scars, or sunburn, a response termed the Koebner phenomenon (Fig. 8-5). Nail changes include reddish-brown psoriatic plaques in the nail bed (oil drop changes), surface pitting, and distal hyperkeratosis (see Fig. 8-148).

The factors that initiate the rapid turnover in epidermal cells that produce the psoriatic plaques are unknown, although an inherited predisposition is suspected and upper respiratory tract and streptococcal infections may precipitate lesions in children, especially in cases of guttate psoriasis. Although the increased epidermal growth causes a thickening of the skin in the psoriatic plaque, there are also areas between the epidermal ridges where the skin is thin and the scale is close to the subepidermal vessels. Thus when the scale is removed, small bleeding points are often seen. This is called the Auspitz sign, and it is the hallmark of psoriasis (Fig. 8-6).

Except in cases of guttate psoriasis, which can be limited to one episode, the course of psoriasis can be chronic and unpredictable, marked by remissions and exacerbations. Thirty-seven percent of adults with psoriasis first develop lesions in childhood.

The Ichthyoses

Ichthyosis refers to a group of genodermatoses characterized by dry, scaly skin. Various types have been identified according to clinical course; histopathology; biochemical markers; and, in some cases, specific genetic mutations.

The Dermatitides

Depending on duration of involvement, the dermatitides are characterized clinically by acute changes (including redness, edema, and vesiculation) and/or chronic changes (such as scaling, lichenification, and increased or decreased pigmentation) in the skin. Microscopically, these disorders are characterized by infiltration of the dermis with inflammatory cells, variable thickening of the epidermis, and scaling.

Atopic Dermatitis (Eczema)

Atopic dermatitis, or eczema, is one of the most common and stressful of all chronic skin disorders in children. This entity is divided into three phases on the basis of the age of the patient, each having a different distribution.

The infantile phase of atopic dermatitis begins between birth and 6 months of age and lasts about 2 or 3 years. Characteristically, the rash is manifest by red, itchy papules and plaques that ooze and crust. Lesions are distributed over the cheeks, forehead, scalp, trunk, and extensor surfaces of the extremities, and patches are often symmetrical (Fig. 8-11).

The childhood phase of atopic dermatitis occurs between ages 4 and 10 years. The dermatitis is typically dry, papular, and intensely pruritic. Circumscribed scaly patches are distributed on the wrists, ankles, and antecubital and popliteal fossae (Fig. 8-12); these patches frequently become secondarily infected, both as a result of the nonintact skin barrier as well as secondary to discrete immunologic differences in children with atopic dermatitis, namely a deficiency in two innate antiviral and antibacterial arms of the skin’s immune system: β-defensins and cathelicidins. Cracking, dryness, and scaling of the palmar and plantar surfaces of the hands and feet are also common (Fig. 8-13). Remission may occur at any time, or the disorder may evolve into a more chronic type of adult dermatitis. Of children with atopic dermatitis, 75% improve between the ages of 10 and 14; the remaining children may go on to develop chronic dermatitis.

The adult phase of atopic dermatitis begins around age 12 and continues indefinitely. Major areas of involvement include the flexural areas of the arms, neck, and legs (Fig. 8-14). Eruptions are sometimes seen on the dorsal surfaces of the hands and feet and between the fingers and toes. Lichenification may be marked (Fig. 8-15).

Other associated findings include xerosis (dryness); ichthyosis vulgaris (see Fig. 8-7); keratosis pilaris, keratin plugging of hair follicles and formation of perifollicular scales over the extensor surfaces of the extremities and sometimes the trunk and abdomen (Fig. 8-16; and see also Fig. 8-25, D); hyperlinearity of the palms; Dennie-Morgan lines (double skin creases under the lower eyelid [see Chapter 4]); and hyperpigmentation and hypopigmentation, which may be marked and at times may be the predominant findings. As a result of their altered immunity in the skin, more than 90% of patients with atopic dermatitis are colonized with Staphylococcus aureus at the time of a flare; for the same cellular reason these patients are also unusually susceptible to cutaneous viral infections including warts, herpes simplex, and molluscum contagiosum. Patients with eczema should be warned to avoid people with cold sores because they are at great risk for developing generalized eczema herpeticum (see Fig. 12-13). Parents of children with eczema who themselves have recurrent herpes simplex lesions should be taught hygienic techniques that reduce the risk of transmitting the virus, even when asymptomatic, as shedding can still occur to their children.

In the rash of pityriasis alba, which is common in patients with atopic dermatitis, inflammatory changes are minimal. Poorly defined, hypopigmented, round or oval scaly patches measuring 2 to 4 cm in diameter are noted most commonly on the face and extremities (Fig. 8-17), although they may involve the trunk as well. These patches fail to enhance with Wood’s lamp examination, which distinguishes them from vitiligo. Lesions are more prominent in children with dark skin and are more noticeable during spring and summer because they do not tan like surrounding skin. Surface scaling is more evident when the skin is dry (especially in winter). The etiology is unknown. Because the disorder is usually asymptomatic and spontaneously resolves in several months to a few years, treatment is usually unnecessary, although moisturizers may help reduce surface scaling.

The cause of atopic dermatitis remains elusive. An immunologic etiology is suggested by the chronic elevation of IgE seen in a majority of patients. Some investigators propose an aberrant cutaneous response to histamine and other mediators of inflammation as a primary mechanism. However, laboratory findings vary from patient to patient and in the same patient at different times in the course of the disease. Atopic dermatitis does seem to occur in families and in association with other atopic conditions in the atopic triad, including asthma, allergic rhinitis, and food allergies, suggesting some degree of genetic predisposition. Pathophysiologically, a number of external factors including dry skin, soaps, wool fabrics, foods, infectious agents, and environmental antigens may act individually or in concert to produce pruritus, which is almost universal in atopic individuals. The resultant scratching leads to the acute and chronic changes typical of atopic dermatitis.

The differential diagnosis of atopic dermatitis includes seborrheic dermatitis, contact dermatitis, pityriasis rosea, psoriasis, fungal infections, Langerhans cell histiocytosis, and acrodermatitis enteropathica. It can be distinguished from seborrheic dermatitis on the basis of the distribution of lesions and associated pruritus; atopic dermatitis spares moist, intertriginous areas such as the axillae and perineum, where seborrheic dermatitis is prominent. Exposure history and distribution help differentiate it from contact dermatitis, as does the discreteness of lesions and their distribution in pityriasis rosea. The thick, silvery scale and Koebner phenomenon help distinguish psoriasis, and central clearing with an active border of red papules, vesicles, and/or pustules helps differentiate tinea corporis. The rash of histiocytosis is crusted, atrophic, and may be more generalized. It is associated with petechiae and is often accompanied by chronically draining ears, hepatosplenomegaly, and lymphadenopathy (see Fig. 8-85 and Chapter 11). The acral and periorificial distribution of lesions and gastrointestinal symptoms help in distinguishing eczema from acrodermatitis enteropathica.

The mainstays of atopic dermatitis treatment are elimination or avoidance of predisposing factors; hydration and lubrication of the skin; the use of antipruritic agents to relieve itching, break the itch–scratch cycle, and normalize sleep patterns; and the use of topical steroids to further relieve itching and decrease inflammation. Pimecrolimus cream and tacrolimus ointment are two agents in the class of nonsteroidal topical immunomodulators that may also dramatically interrupt the itch–scratch cycle. They have been approved as second-line therapy for the management of atopic dermatitis in children older than 2 years of age. Use of these agents should be accompanied by an explanation of the boxed warning regarding the theoretical risk of lymphoma and skin cancer. However, these tumors have been seen only with prolonged systemic use at very high doses.

All children with atopic dermatitis should be monitored closely for secondary bacterial infection, which must be treated promptly with topical or systemic antibiotics to prevent progression to cellulitis. The use of a hyperdiluted bleach (1 to 2 ounces in a 30-gallon tub of water) bath several times per week is a cost-effective way of preventing infection in patients with atopic dermatitis. Herpes simplex can also occur as a secondary infection over atopic dermatitis and can rapidly disseminate in patients with active atopic dermatitis, resulting in the severe disorder known as eczema herpeticum (see Fig. 12-13). Hence, patients’ families should be warned to have their children avoid contact with people with cold sores, and if parents have recurrent herpes labialis, they should be instructed in strict hand-washing precautions. Further, patients should be treated with antiviral agents at the first sign of infection with herpes simplex.

Dyshidrotic eczema and nummular eczema are clinical patterns of atopic dermatitis, and juvenile palmo–plantar dermatosis and lip-licking and thumb-sucking eczema represent irritant dermatitides that may be associated with atopic dermatitis.


Seborrheic dermatitis is characterized by a red scaling eruption that occurs predominantly on hair-bearing and intertriginous areas such as the scalp; eyebrows; eyelashes; perinasal, presternal, and postauricular areas and the neck; axillae; and groin. Lesions often involve the intertriginous areas of the arms, legs, neck, and trunk, and occasionally become generalized (Fig. 8-23, AD). In affected infants, scalp lesions consist of a thick, tenacious, scaly dermatitis that is often salmon colored and is commonly known as cradle cap (Fig. 8-24, A and B). In adolescents the dermatitis may manifest as dandruff or flaking of the eyebrows, postauricular areas, or flexural areas.

Although the pathogenesis of seborrheic dermatitis is unknown, Pityrosporum and Candida species have been implicated as causative agents. A role for neurologic dysfunction is suggested by the increased incidence and severity in neurologically impaired individuals.

The dermatitis of seborrhea is usually nonpruritic and mild in nature. Most cases respond to topical steroids, and many clear spontaneously, although residual postinflammatory hypopigmentation may persist for weeks or months thereafter (see Fig. 8-125). Some practitioners find that use of a topical antifungal cream or wash, as well as a low-potency topical steroid, hastens resolution. Antiseborrheic shampoos may also be helpful for patients with scalp involvement. In infants and young children, atopic dermatitis can have a greasy, scaly appearance and may be confused with seborrhea. However, infantile atopic dermatitis produces intense pruritus and invariably spares moist sites such as the diaper area and axillae. The two are often present simultaneously in the same patient. The differential diagnosis of seborrhea includes Langerhans cell histiocytosis (in which the rash is generalized, in part petechial, and usually associated with chronic draining ears and hepatosplenomegaly) and tinea corporis (in which lesions usually are more circumscribed, with an active border and central clearing). Scalp lesions may be difficult to differentiate from psoriasis.

Hyper-IgE (Job) Syndrome

Job syndrome is a rare genetic disorder with prominent cutaneous manifestations. It has been linked to a mutation on chromosome 4q and is usually inherited as an autosomal dominant trait with variable severity of expression. Affected patients have abnormalities of the immune response involving T lymphocytes, neutrophils, cytokines, and interleukins. They also have variably but significantly elevated levels of serum IgE and circulating eosinophils.

Dermatologic features include a pruritic dermatitic rash that shares features with both atopic dermatitis and seborrhea, and which tends to develop shortly after birth (earlier than seborrhea and atopic dermatitis). It rapidly becomes superinfected with S. aureus, which results in the formation of weeping, crusting, and folliculitic lesions, as well as cutaneous abscesses (Fig. 8-25, AD). In contrast to furuncles in patients with a normal immune response, the abscesses in children with Job syndrome cause little pain and show few signs of inflammation. Development of mucocutaneous candidiasis is also common. Other clinical manifestations include recurrent/chronic infections such as bronchitis, pneumonia (with pneumatoceles), sinusitis, otitis, gingivitis, dental abscesses, septic arthritis, and osteomyelitis. Decreased bone density is the source of multiple fractures, which cause remarkably little pain. With age and growth, facial features tend to coarsen (see Fig. 4-54, E) and scoliosis is common.

Treatment is aimed at controlling infections and ameliorating symptoms. The major differential diagnostic consideration is Langerhans histiocytosis (see Fig. 8-85).

Pityriasis Rosea

Pityriasis rosea is a benign, self-limited disorder that can occur at any age but is more common in adolescents and young adults. A prodrome of malaise, headache, and mild constitutional symptoms occasionally precedes the rash. The typical eruption begins with the appearance of a “herald patch” (Fig. 8-26, A), which is a large, isolated, oval lesion, usually pink in color and slightly scaly; it may occur anywhere on the body. On occasion, it clears centrally, simulating tinea corporis. From 5 to 10 days later, other smaller lesions appear on the body, frequently concentrated over the trunk but also seen on the proximal extremities, especially the thighs (see Fig. 8-26, BG). On occasion, lesions predominate on the face, groin, and/or distal extremities including the palms and soles, a phenomenon known as inverse pityriasis, which is more common in African-American patients. Pityriasis lesions begin as small, round papules that enlarge to oval plaques up to 1 to 2 cm in size, with a scaly surface. They are usually somewhat raised but can be macular, and they can be erythematous, hyperpigmented, or hypopigmented. The long axes of the ovals tend to run parallel to the lines of the cleavage of the skin, creating a “Christmas tree” pattern over the thorax (Fig. 8-26, C and D). The rash reaches its peak in several weeks, and then slowly fades over 4 to 8 weeks. The average total duration is 2 to 3 months. Oral erythromycin or doxycycline and small doses of ultraviolet light may hasten the disappearance of the eruption. Although the cause is unknown, the peak incidence in late winter and the low recurrence rate favor an infectious etiology.

Other eruptions that can resemble pityriasis rosea include guttate psoriasis, benign parapsoriasis, viral exanthems, measles-like (morbilliform) drug eruptions, and secondary syphilis (see Fig. 18-36). Secondary syphilis should specifically be considered when a patient presents with a rash resembling pityriasis rosea and the palms and soles are involved. As noted earlier, the appearance of the herald patch may simulate tinea corporis, but a potassium hydroxide (KOH) preparation is negative.

Contact Dermatitis

Contact dermatitis refers to a group of conditions in which a dermatitic or inflammatory reaction in the skin is triggered by direct contact with environmental agents. In the most common form, irritant contact dermatitis, changes in the skin are induced by caustic agents such as acids and alkalis, hydrocarbons, and other primary irritants. Anyone exposed to these agents in a high enough concentration for a long enough period will ultimately develop a contact dermatitis. The rash is usually acute, with well-demarcated erythema, crusting, and/or blister formation.

In contrast, allergic contact dermatitis is a T-lymphocyte–mediated immune reaction to an antigen coming into contact with the skin. Although patients typically present with acute onset of erythema, vesiculation, and pruritus, in some cases they delay seeking care until after the rash has become chronic with scaling, lichenification, and pigmentary changes. Often, the allergen is obvious, as is the case with poison ivy or nickel jewelry. However, in other cases, careful questioning may be required to detect the inciting agent.

The initial reaction occurs after a 7- to 14-day period of sensitization in susceptible individuals. Once sensitization has occurred, reexposure to the allergen provokes a more rapid reaction, sometimes within hours. This is a classic example of type IV (delayed) hypersensitivity (see Chapter 4).

Rhus Dermatitis (Poison Ivy)

The most common type of allergic contact dermatitis in the United States is poison ivy, or rhus dermatitis. This typically presents as linear streaks of erythematous papules and vesicles (Fig. 8-27, A); however, with heavy exposure, the rash may appear in relatively large patches (Fig. 8-27, B and C). When lesions involve the skin of the face or genitalia, impressive swelling can occur (Fig. 8-27, D).

Direct contact with the sap of poison ivy, poison oak, or poison sumac from leaves, stems, or roots (whether the plant is alive or dead) produces the dermatitis (Fig. 8-28). Contact with clothing that has brushed against the plant, with logs or railroad ties on which the vine has been growing, or with smoke from a fire in which the plant is being burned are other means of exposure. Areas of skin exposed to the highest concentration of plant oil develop changes first. Other sites that received lower doses then vesiculate in succession, giving the illusion of spreading. This is not the case, however, as within about 20 minutes of initial contact, the rhus oil becomes tissue-fixed to the epithelial cells and cannot be spread farther. Thorough washing within minutes of exposure can prevent fixation, and hence, the eruption. On occasion the oil can oxidize, leaving a black discoloration superimposed on the contact dermatitis; this is known as “black dot” or “urushiol” dermatitis.

Other Common Causes of Contact Dermatitis

Other common offending agents are nickel (Fig. 8-29), rubber (Fig. 8-30), glues and/or dyes in shoes or diapers (Fig. 8-31), ethylenediamine in topical lotions, neomycin, and topical anesthetics (Fig. 8-32). Paraphenylenediamine dye used in amateur henna tattoos is an increasingly common cause of contact dermatitis among adolescents, and the pattern reflects the image of the original tattoo (Fig. 8-33).

Photocontact Dermatitis and Phototoxic Reactions

Photocontact or photoallergic dermatitis is a true cell-mediated delayed hypersensitivity reaction and necessitates a 7- to 10-day period of sensitization, after which sun exposure may precipitate development of a dermatitis. When caused by systemically administered drugs, it characteristically erupts in a symmetrical distribution on the face, the V of the neck, and the arms and legs distal to the end of shirt sleeves and shorts. Potentially causative agents include the tetracyclines, isotretinoin, sulfonylureas, thiazides, nonsteroidal antiinflammatory drugs, fluoroquinolones, and griseofulvin. Topical photosensitizers (sunscreens with PABA esters or oxybenzone; fragrances in soaps, creams, lotions, or cosmetics; coal tar; furocoumarins; and halogenated salicylanilides in germicidal soaps) produce localized patches of dermatitis when used on sun-exposed sites (Fig. 8-34).

Phototoxins, when applied to the skin, are the source of a nonimmunologic exaggerated sunburn reaction in which the initial erythema progresses to hyperpigmentation. Of these, phytophotodermatitis is the most common. In this form, plant-derived photosensitizers, psoralens, found in the juice of lemons, limes, figs, dill, parsley, parsnips, carrots, and celery, are responsible for the reaction. Typically a child is touched by a parent who has been cutting the fruit, herbs, or vegetables, thereby getting the juice on the child’s skin. Subsequent exposure to sunlight then results in the appearance of erythematous macules, with or without accompanying bullae, which then go on to become hyperpigmented. These patches often have bizarre or hand/finger-shaped patterns that can mimic child abuse (see Fig. 6-66).

Fungal Infections

Two types of fungal organisms produce clinical cutaneous disease: dermatophytes and yeasts. Dermatophytes include the tinea or ringworm fungi, and yeasts include Candida species, which are associated with diaper dermatitis and Pityrosporum species, which cause tinea versicolor. Both Candida and Pityrosporum have been implicated as partially causative in seborrhea.

Tinea Corporis

Tinea corporis is a superficial fungal infection of the nonhairy or glabrous skin. It has been labeled “ringworm” because of its characteristic configuration consisting of pruritic, annular lesions with central clearing and an active border made up of microvesicles that rupture and then scale (Fig. 8-35, AC). Lesions, which may be single or multiple, typically begin as pruritic red papules or pustules that rupture and evolve to form papulosquamous lesions, which are also pruritic. These then spread out from the periphery as new vesicles form at their outer margins, and at the same time begin to clear centrally (see Fig. 8-35, D and E). Over a period of several weeks, the patches may expand up to 5 cm in diameter. Tinea corporis can be found in any age group and is usually acquired through direct human contact (Trichophyton tonsurans) or from an infected pet, such as a kitten.

Clinically, tinea may be differentiated from atopic dermatitis by the propensity for autoinoculation from the primary patch to other sites on the patient’s skin, by the spread to close contacts, and by the central clearing noted in many lesions. Moreover, the rash of atopic dermatitis tends to be symmetrical, chronic, and recurrent in a flexural distribution. Unlike tinea, patches of nummular eczema are self-limited and do not clear centrally. The herald patch of pityriasis rosea is often mistaken for tinea. However, it is KOH negative, and the subsequent development of the generalized rash with its characteristic truncal distribution is distinctive (see Fig. 8-26). The clinical pattern, findings, and chronic nature of psoriasis and seborrhea help differentiate them from tinea. Although granuloma annulare produces a characteristic ringed eruption, on palpation the lesions are firm and usually asymptomatic. They tend not to show epidermal changes other than occasional slight scaling (see Fig. 8-86).

The diagnosis of tinea corporis is confirmed by KOH examination of skin scrapings. The first step is to obtain material by scraping the loose scales at the margin of a lesion (Fig. 8-36, A). These should be mounted onto the center of a glass slide, with one or two drops of 20% KOH solution added. Next, a glass coverslip is applied and gently pressed down with the eraser end of a pencil to crush the scales (Fig. 8-36, B). The clinician then heats the slide, taking care not to boil the KOH solution, and again the coverslip is pressed down. When viewing the slide under the microscope, the clinician sets the condenser and light source at low levels to maximize contrast, with the objective at ×10. On focusing up and down, true hyphae are seen as long, branching, often septate rods of uniform width that cross the borders of epidermal cells (Fig. 8-37). Cotton fibers, cell borders, or other artifacts may be falsely interpreted as positive findings.

Tinea infections on glabrous skin readily respond to topical antifungal creams such as miconazole, clotrimazole, econazole, naftifine, ketoconazole, and ciclopirox. When lesions are multiple and widespread, oral therapy with griseofulvin is indicated. Itraconazole, terbinafine, and fluconazole are good alternatives for systemic antifungal therapy. Like griseofulvin, they are effective against most ringworm organisms, but unlike griseofulvin, these medications are concentrated in skin, hair, and nails for weeks to months after they are discontinued. Tinea infections should never be treated with the topical products that combine an azole antifungal with a medium or high-potency topical steroid. Paradoxically, these agents increase the likelihood that the fungal infection will spread deeper within the skin and be more resistant to topical therapy, a process called tinea incognito or Majocchi granuloma. At this stage oral therapy often becomes necessary to clear the infection.

Tinea Pedis

Commonly referred to as athlete’s foot, tinea pedis is a fungal infection of the feet with a predilection for the web spaces between the toes. Tinea pedis is quite common in adolescence, somewhat less so in prepubertal children. The infecting organisms are acquired from contaminated shower, bathroom, locker room, and gym floors, and their growth is fostered by the warm, moist environment of shoes.

In some cases, scaling and fissuring predominate; in others, vesiculopustular lesions and maceration are found, especially in the web spaces between the third, fourth, and fifth toes. The infection begins between and along the sides of the toes, where it may remain (Fig. 8-38, A). However, lesions can extend over the dorsum of the foot (see Fig. 8-38, B) and may involve the plantar surface as well, particularly the instep and ball of the foot. Patients complain of a combination of burning and itching, which is frequently intense.

This diagnosis often can be made on clinical grounds and is confirmed by KOH preparation of skin scrapings. The mainstays of treatment are topical antifungal creams or powders, as well as measures designed to reduce foot moisture. The latter include careful drying of the feet after bathing, wearing cotton rather than synthetic socks, and wearing shoes that do not promote sweating or, better still, sandals. In patients with severe inflammatory lesions, oral antifungal agents may be required. Onychomycosis (see Fig. 8-144) responds well only to oral agents and requires treatment for 4 months, occasionally longer (see Disorders Affecting the Nails, later). Secondary bacterial infection (particularly with gram-negative organisms) may be a problem.

Tinea pedis is distinguished from contact dermatitis of the feet by virtue of the fact that the latter spares the interdigital web spaces (see Fig. 8-31). Dyshidrosis can have a similar distribution, but the KOH preparation is negative (see Fig. 8-18).

Tinea Versicolor

Tinea versicolor is a common dermatosis characterized by multiple small, oval, scaly patches measuring 1 to 3 cm in diameter, usually located in a guttate or raindrop pattern on the upper chest, back, and proximal portions of the upper extremities of adolescents and young adults (Fig. 8-39, A and B). However, all ages may be affected, including infants. Facial involvement occurs occasionally. The eruption is caused by a dimorphous form of Pityrosporum. Warm, moist climates, pregnancy, immunodeficiency, and genetic factors predispose people to the development of infection.

The rash is usually asymptomatic, although some patients complain of mild pruritus. Typically, patients go to the physician because they are bothered by the cosmetic appearance of the lesions. Lesions may be light tan, reddish, or lightly discolored, giving rise to the term versicolor. They are darker than surrounding skin in non–sun-exposed areas (Fig. 8-39, C) and lighter in areas that have tanned on exposure to sunlight (see Fig. 8-39, A and B).

The diagnosis of tinea versicolor can generally be made on the basis of the clinical appearance of lesions and their distribution. It can be confirmed by examining the lesions under a Wood’s lamp, which reveals a characteristic tan to salmon-pink glow but no enhancement of the discoloration as in vitiligo. Although pathogenesis of the color change under a Wood’s lamp is not fully understood, the fungus is known to produce a substance that interferes with tyrosinase activity and subsequent melanin synthesis. A KOH preparation of the surface scale demonstrates short hyphal and yeast forms that resemble spaghetti and meatballs (Fig. 8-40).

The differential diagnosis of tinea versicolor includes postinflammatory hypopigmentation and vitiligo. The history and distribution help to distinguish tinea versicolor from postinflammatory hypopigmentation; the presence of fine superficial scaling and some residual pigmentation (even in hypopigmented areas) that does not enhance with Wood’s lamp examination helps rule out vitiligo.

Topical antiyeast agents such as selenium sulfide produce rapid clearing of the superficial lesions. Localized eruptions may be treated with topical antifungal creams such as miconazole, clotrimazole, or econazole, and recalcitrant cases respond to oral fluconazole or itraconazole. Patients must be counseled about the high risk of recurrence, which often necessitates ongoing prophylactic selenium sulfide washes for several days each month. They should also be reminded that pigmentary changes may take months to clear, even after eradication of the fungus.

Diaper Dermatitis

Because the diaper area is warm, often moist, and frequently contaminated by feces laden with organisms, diaper dermatitis is one of the most common skin disorders of infancy and early childhood.

Irritant Diaper Dermatitis

The diaper area is a prime target for irritant dermatitis because it is bathed in urine and stool and occluded by plastic diaper covers. Failure to change diapers frequently is a major predisposing factor because it provides time for fecal bacteria to form ammonia by splitting the urea in urine. Harsh soaps, irritant chemicals, and detergents can contribute to the process. Moderate to severe diarrhea is another predisposing condition. The erythema; scaling; and, at times, maceration characteristic of irritant diaper dermatitis are usually confined to the convex surfaces of the perineum, lower abdomen, buttocks, and proximal thighs, sparing intertriginous areas (Fig. 8-41). When neglected, this may progress, with further skin breakdown and ulceration. Frequent diaper changes; gentle, thorough cleansing of the area; and application of lubricants and barrier pastes usually result in clearing of the dermatitis. A short course of low-potency steroids may hasten resolution, but this must be discontinued after a week or so and then followed by prevention with thick, unfragranced zinc oxide pastes as a barrier.

Persistent diaper dermatitis that does not resolve with conservative therapy may be due to other disorders such as contact dermatitis to the dyes present in the diaper (this has become increasingly common), candidiasis, seborrheic dermatitis, and psoriasis. These should be suspected particularly when intertriginous areas are involved.

Candidal Diaper Dermatitis

Candidal diaper dermatitis appears as a bright red eruption, with sharp borders and pinpoint satellite papules and pustules (Fig. 8-42, A and B). Examination of pustule contents by KOH preparation reveals the typical budding yeasts and pseudohyphae of Candida organisms (Fig. 8-43). Candidal diaper dermatitis is occasionally associated with oral thrush, and it is a common sequela of oral or parenteral antibiotic therapy. One should suspect a secondary invasion by Candida albicans whenever intertriginous areas are involved or when a diaper rash fails to respond to symptomatic treatment. Most cases respond well to topical antifungal therapy, but the occasional resistant case may require a brief course of oral medication.

Seborrheic Diaper Dermatitis

Seborrheic diaper dermatitis is characterized by salmon-colored lesions with a yellowish scale. The rash is particularly prominent in the intertriginous areas (see Fig. 8-23, B). Although concurrent infection with Candida or Pityrosporum is likely, satellite lesions are usually not seen. Typically, seborrheic dermatitis of the scalp, face, and postauricular areas is seen in association with this form of diaper dermatitis.

Psoriatic Diaper Dermatitis

Psoriasis occasionally begins as an erythematous, scaling eruption in the diaper area (Fig. 8-45, A and B), which is clinically indistinguishable from seborrheic diaper dermatitis. Perhaps because the diaper area tends to be moist, the thick silvery scale typical of psoriatic lesions at other sites is not seen. Although lesions may develop subsequently on the trunk and extremities, the rash may persist for months in the diaper area alone. Failure of a seborrheic-like diaper rash to respond to empiric therapy over several weeks or months should raise psoriasis as a diagnostic possibility. Skin biopsy is the only way to confirm the diagnosis.

Lichenoid Eruptions

Vesiculopustular Disorders

Vesiculopustular eruptions range from benign, self-limited conditions to life-threatening diseases. Early diagnosis, especially in the young child, is mandatory. Systematic evaluation of the clinical findings and a few rapid diagnostic techniques allow these various disorders to be readily differentiated from one another.

Bacterial Infections

Several common cutaneous bacterial infections present with vesiculopustular reactions as well. In impetigo, the eruption tends to be discrete and localized, whereas in staphylococcal scalded skin syndrome (SSSS) it tends to be associated with a diffuse erythroderma. A Gram stain of material aspirated from bullae or removed from the base of an impetiginous lesion is positive for organisms. However, in patients with SSSS, the organism must be sought from noncutaneous colonized locations (nasopharynx, conjunctivae, sinuses) because the diffuse cutaneous blistering is due to elaboration of the toxin epidermolysin by the infecting organism and not to the organism’s direct action within individual lesions (see Chapter 12 and Fig. 12-18).

Erythema Multiforme

Erythema multiforme (EM) is a distinctive, acute hypersensitivity syndrome that, in both children and adults, is most frequently triggered by recurrent herpes simplex virus (HSV) infection. EM should not be confused with either Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN), which are severe, potentially life-threatening eruptions characterized by variably widespread cutaneous blistering and sloughing, and by involvement of multiple mucous membranes.

The classic eruption of EM is symmetrical and may occur on any part of the body. However, the dorsum of the hands and feet and the extensor surfaces of the arms and legs are affected most commonly. Involvement of the palms and soles also is typical. The initial lesions are dusky red macules or erythematous wheals that evolve into iris- or target-shaped lesions, the hallmark of EM (Fig. 8-51, A). In many instances the initial crop of lesions simulates diffuse urticaria, although EM lesions are typically much less pruritic, if at all, and ultimately they become painful and persistent, in contrast to true urticarial lesions, which remain pruritic and tend to migrate over a 24-hour period. The target configuration is due to formation of a central depression that may be blue, violaceous, or white, whereas the elevated periphery tends to remain erythematous. In some cases, vesicles or bullae develop centrally, and in others the peripheral rings may vesiculate or become bullous (Fig. 8-51, B and C). The eruption continues in crops that last from 1 to 3 weeks. In most patients the disease is self-limited, and systemic manifestations are relatively mild, consisting of low-grade fever, malaise, and myalgia. Mucous membranes tend to be spared, although, on occasion, the oral mucosa may be mildly involved. The major differential diagnosis is urticaria, which does not demonstrate three discrete zones of color change to form a target, as do lesions of true erythema multiforme.

< div class='tao-gold-member'>

Jul 11, 2016 | Posted by in PEDIATRICS | Comments Off on Dermatology
Premium Wordpress Themes by UFO Themes