Ichthyosis Vulgaris

Ichthyosis vulgaris occurs secondary to a mutation in filaggrin and is transmitted as an autosomal dominant trait and affects about 0.5% of the population. Although the rash is not present at birth, by 3 months of age thick, fishlike scales may be apparent on the shins and extensor surfaces of the arms (Fig. 8-7). On occasion, scales become more generalized, involving the trunk, but the flexures are usually spared. Lesions tend to flare during the winter (because of the drying effect of central heating) and improve during the summer, particularly with increasing age. Biopsy of involved skin shows retention hyperkeratosis and a thinned granular layer in the epidermis. Liberal use of topical emollients usually keeps pruritus and scaling under control.

Figure 8-7 Ichthyosis vulgaris. The typical fish scale appearance is seen in this close-up of a fair-skinned patient’s shin.

X-linked Ichthyosis

X-linked ichthyosis occurs in 1 in 6000 males as a result of a mutation in the enzyme steroid sulfatase, although findings are occasionally present in hemizygous female carriers. Affected newborns usually present between 3 and 12 months of age with generalized “dirty” brown scales, particularly on the lateral neck, abdomen, back, and anterior legs and feet (Fig. 8-8). The central face and flexures are spared. Skin biopsy demonstrates an increased granular layer and stratum corneum, and biochemical studies demonstrate decreased or absent steroid sulfatase in the serum and skin. Children with X-linked ichthyosis are at increased risk of undescended testes as well (even independent of this risk) as testicular cancer. Decreased or absent steroid sulfatase activity during fetal life may result in decreased placental estrogen and a delay in onset of labor.

Figure 8-8 X-linked ichthyosis. “Dirty” brown scales persist on the flanks, elbows, and shoulders despite the use of topical lubricants.

Lamellar Ichthyosis

Lamellar ichthyosis is a rare autosomal dominant disorder occurring in fewer than 1 in 250,000 births as a result of a mutation in keratinocyte transglutaminase-1. Infants are usually born with a collodion membrane (see Fig. 8-93). During the first month of life, thick, brownish gray, sheetlike scales with raised edges appear. Scaling is prominent over the face, trunk, and extremities (Fig. 8-9). In contrast to ichthyosis vulgaris, the flexural areas are involved (Fig. 8-9, B). Eversion and fissuring of the eyelid margins (ectropion) and lips (eclabium) are common complications (Fig. 8-9, C). The palms and soles show thick keratoderma with fissuring. Some improvement of the scaling occurs with age, and topical keratolytics such as lactic acid and salicylic acid may provide some benefit. Severe cases may respond to the administration of systemic retinoids such as acitretinoin or isotretinoin.

Figure 8-9 Lamellar ichthyosis. A, Note the thick, brownish-black scales covering the entire skin surface. B, Flexural involvement helps differentiate lamellar ichthyosis from ichthyosis vulgaris. C, Ectropion (note the eversion of the lower lids) is a unique finding in this form of the disorder.

Epidermolytic Hyperkeratosis

Epidermolytic hyperkeratosis is a rare autosomal dominant form of ichthyosis characterized by the development of generalized, thick, warty scales and intermittent blistering with severe involvement of the flexures (Fig. 8-10). In newborns, blisters and erosions may be widespread and must be differentiated from epidermolysis bullosa or herpes simplex. Histologically, massive hyperkeratosis is associated with ballooning of squamous cells and formation of microvesicles. Epidermal turnover is also markedly increased. The mainstay of treatment includes use of keratolytics, lubricants, and antibiotics for secondary infection, which is common and usually caused by Staphylococcus aureus. Oral retinoids may also significantly decrease scaling.

Figure 8-10 Epidermolytic hyperkeratosis is characterized by thick, warty scales and intermittent blistering. The flexural creases are particular sites of involvement.

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).

Figure 8-11 Infantile atopic dermatitis or eczema. A, This infant has an acute, weeping dermatitis on the cheeks and forehead. B and C, Involvement of the trunk and the extremities, with erythema, scaling, and crusting, is evident. Usually the diaper area is the only portion of the skin surface that is spared.

(B and C, From Fireman P, Slavin RG: Atlas of allergies, New York, 1991, Gower.)

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.

Figure 8-12 Childhood atopic dermatitis with lesions on the arms (A) and the legs (B). In childhood, eczema involves the flexural surfaces of the upper and lower extremities. The neck, ankles, wrists, and posterior thighs also may be severely affected.

(A, From Fireman P, Slavin RG: Atlas of allergies, New York, 1991, Gower; B, courtesy Michael Sherlock, MD, Lutherville, Md.)

Figure 8-13 Involvement of the hands and feet in eczema. A, A 10-year-old atopic child has lichenification of the skin over the dorsum of his fingers and “buff” nails from chronic rubbing. B, This infant has numerous red excoriated lesions over the soles of his feet.

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).

Figure 8-14 Adult atopic dermatitis. Erythematous excoriated plaques with indistinct borders are seen in the antecubital areas. Note the dried blood from recent excoriation.

Figure 8-15 Lichenification refers to marked thickening of the skin seen in areas of atopic dermatitis that have been subject to chronic scratching. In addition, this patient demonstrates significant postinflammatory hyperpigmentation.

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.

Figure 8-16 Keratosis pilaris. A, Diffuse fine follicular papules and sandpaper scaling are seen on the extensor surface of the arm of this adolescent. B, In this 5-year-old boy, characteristic white follicular papules are more widely spaced and more prominently seen on the extensor surface of his thighs and upper arms. His mother had similar lesions.

(From Cohen BA, Lehman CU, editors: DermAtlas, Baltimore, 2000-2011, Johns Hopkins University. http://dermatlas.med.jhmi.edu/derm.)

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.

Figure 8-17 Pityriasis alba. In some atopic individuals, subtle inflammation may result in the development of poorly demarcated, hypopigmented patches that are covered by a fine superficial scale.

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.

Dyshidrotic Eczema

Dyshidrosis is a severely pruritic, chronic, recurrent, vesicular eruption affecting the palms, soles, and lateral aspects of the fingers and toes. Characteristically, the vesicles are symmetrical, multilocular, and 1 to 3 mm in diameter. These lesions rupture, leaving scales and crust on an erythematous base (Fig. 8-18). Pathologically, this eruption demonstrates spongiotic vesicles and normal eccrine sweat glands. The cause is unknown; however, frequent exposure to water, wet or sweat-soaked shoes, or chemicals (on the hands) may trigger or exacerbate the condition. Hyperhidrosis, or excessive sweating of the palms and soles, may also play a role. Treatment is similar to that for acute atopic dermatitis.

Figure 8-18 Dyshidrosis. Chronic cracking, oozing, and scaling develop after the initial tiny pruritic vesicles have been scratched.

Nummular Eczema

Nummular eczema is an acute papulovesicular eruption named for its coin-shaped configuration and probably also represents another clinical pattern found in atopic individuals. Lesions are intensely pruritic, well-circumscribed, round to oval, red, scaly patches studded with 1- to 3-mm vesicles (Fig. 8-19, A). They are usually located on the extensor thighs or abdomen of children who also may have atopic dermatitis. Vigorous scratching causes excoriation and crusting (Fig. 8-19, B). Lack of central clearing helps distinguish these lesions from tinea corporis (see Fig. 8-35). Although the rash is often resistant to therapy, it may respond to the treatment for acute dermatitis outlined previously.

Figure 8-19 Nummular eczema. A, Round- to oval-shaped lesions studded with tiny vesicles are typically located over the extensor thighs or abdomen. They do not show central clearing. B, Vigorous scratching results in excoriation with weeping and crusting.

(A, Courtesy Michael Sherlock, MD, Lutherville, Md.)

Juvenile Plantar–Palmar Dermatosis

Juvenile plantar–palmar dermatosis (“sweaty sock syndrome”) is common in toddlers and school-age children. Chronic, red scaly patches with cracking and fissuring typically begin on the anterior plantar surfaces of the feet and big toes (Fig. 8-20). The palms may be involved as well, although less severely. Although the cause is unknown, the condition is triggered by excessive sweating and/or repeated wetting of the skin inside the child’s shoes (especially those made of synthetic materials that do not breathe), followed by drying of the skin at night. Some children experience flares in the summer, whereas in others the flares occur in winter. Consequently, the mainstay of treatment consists of emollients for prevention and occasional application of topical steroids when intense inflammation is present during flares.

Figure 8-20 Juvenile plantar dermatosis. This variant of atopic dermatitis is usually localized to the plantar surfaces of the toes and feet. Note the glistening erythema, scaling, and fissuring. In some patients the palms may be affected as well.

Lip-licking and Thumb-sucking Eczema

The repeated wetting and drying from persistent lip licking (especially in winter) or thumb sucking can produce eczematoid changes of the perioral skin (Fig. 8-21) or the skin of the involved thumb (Fig. 8-22). Lip-licking eczema can be the result of a habit or can be a manifestation of anxiety, and sources of stress should be explored on history taking. Once the process begins, it can become a vicious cycle as the child licks with increasing frequency to moisten the dry skin.

Figure 8-21 Lip-licking eczema. The perioral skin is inflamed, scaly, and thickened as a result of repetitive licking of the lips.

(Courtesy Douglas W. Kress, MD, University of Pittsburgh Medical Center.)

Figure 8-22 Thumb-sucking eczema. Repeated wetting and drying from persistent thumb sucking result in eczematoid changes with cracking, fissuring, and lichenification.

(Courtesy Michael Sherlock, MD, Lutherville, Md.)

Seborrhea

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, A–D). 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.

Figure 8-23 Seborrhea. This slightly greasy, red, scaling eruption typically involves the hair-bearing areas of the face, axilla (A), and diaper area (B). C, The intertriginous folds of the neck are another common site of involvement. D, Postauricular lesions are common and often become secondarily infected as in this case, which grew group A β-streptococci.

(D, Courtesy Michael Sherlock, MD, Lutherville, Md.)

Figure 8-24 Seborrhea of the scalp. A, Note the oily appearance and salmon-pink hue. Numerous scales, some adherent to the scalp and many interlaced through the baby’s hair, are present. B, In this infant the scales have formed a thick crust, and erythema is less evident.

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, A–D). 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.

Figure 8-25 Job syndrome. This infant with markedly elevated IgE experienced early onset of a pruritic dermatitis that shared clinical features with both seborrhea and atopic dermatitis. A, Note the erythema and scaliness, the evidence of excoriation from scratching, and the perinasal crusting due to Staphylococcus aureus infection. B, In this view, in addition to the erythema, scaling, and thickening of the skin, there are weeping areas around the ear and crusts and scabs over the scalp. Note also the purulent ear drainage. C, He also had crusted palmar lesions. D, The skin over his abdomen had the classic features of keratosis pilaris.

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, B–G). 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.

Figure 8-26 Pityriasis rosea. A, The large herald patch on this boy’s back shows evidence of central clearing, mimicking tinea corporis. B, Numerous oval lesions with their long axes oriented along lines of skin cleavage are seen over the trunk of this adolescent. C and D, This feature creates the appearance of a fir tree distribution on the back. E–G, Lesions can be raised, macular, or scaly and can be erythematous or hyper- or hypopigmented.

(A and C, Courtesy Douglas W. Kress, MD, University of Pittsburgh Medical Center; E and F, courtesy Michael Sherlock, MD, Lutherville, Md.)

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).

Figure 8-27 Poison ivy, or rhus dermatitis. A, Linear streaks of pruritic vesicles are typical of contact dermatitis caused by exposure to a plant. B and C, With heavier exposure, however, the eruption can develop in relatively large patches. Also note the microvesicular appearance of the facial lesion in the child shown in C. D, Reactions involving the face and genitalia can provoke impressive swelling.

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.

Figure 8-28 A, Poison ivy. The plant has characteristic shiny leaves in groups of three. It may resemble a vine, a low shrub, or a bush. B, Poison oak. This also has leaves in groups of three, although the edges tend to be more scalloped than those of poison ivy.

(B, Courtesy Mary Jelks, MD.)

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).

Figure 8-29 Nickel contact dermatitis. The location and distribution of the rash are often helpful in determining the cause of a contact dermatitis. In this case wrist lesions were triggered by the nickel in her bracelet clasp.

Figure 8-30 Rubber contact dermatitis. This child had become sensitized to the elasticized waist bands of his underpants.

Figure 8-31 Contact dermatitis of the foot due to glues/dyes in shoes. A, This adolescent became sensitized to the glue under the insoles of his shoes. Note the sparing of the instep. B, Another child had a similar problem with the toe reinforcers in his shoes. Note that the web spaces are spared.

(A, Courtesy Michael Sherlock, MD, Lutherville, Md; B, courtesy Douglas W. Kress, MD, University of Pittsburgh Medical Center.)

Figure 8-32 Contact dermatitis due to topical anesthetics. This adolescent became sensitized to the topical anesthetic Lanacaine in a moisturizing cream that she applied to her hands daily. Note the line of demarcation at the wrist.

Figure 8-33 Contact dermatitis due to henna dye. This young teenager developed vesicular lesions in the precise pattern of a henna tattoo she had had applied 2 weeks earlier.

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).

Figure 8-34 Photocontact dermatitis. This boy developed contact dermatitis after sun exposure while outside for a day of swimming. The offending agent was found to be in his soap.

(Courtesy Michael Sherlock, MD, Lutherville, Md.)

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).

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, A–C). 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.

Figure 8-35 Tinea corporis. The characteristic annular lesions show many variations in appearance. A, This lesion has a raised, active border and shows partial central clearing. B, In another case the inflammatory response is intense, and only a little central clearing is seen. C, The lesion shown here involving the palm and flexor surfaces of the fingers is macular and scaly and has a sharply circumscribed proximal border. D, The evolution of lesions from papules and pustules into larger papulosquamous patches is seen on this girl’s leg. E, In another child, small papules, plaques that have not cleared centrally, and larger lesions with varying degrees of central clearing are seen.

(B, Courtesy Douglas W. Kress, MD, University of Pittsburgh Medical Center; D, courtesy Michael Sherlock, MD, Lutherville, Md.)

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.

Figure 8-36 Potassium hydroxide (KOH) preparation. A, Small scales should be scraped from the edge of the lesion onto a microscope slide. B, To more easily visualize the fungus, the scales should be crushed, making a thin layer of cells.

Figure 8-37 Positive KOH preparation of skin scrapings. Fungal hyphae are seen as long septate branching rods at the margins and center of the scales.

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.

Figure 8-38 Tinea pedis. A, Cracking and scaling are seen in the web space. B, In this patient the lesions began in the web spaces but then extended onto the dorsum of the foot. Note the active border.

(B, Courtesy Douglas W. Kress, MD, University of Pittsburgh Medical Center.)

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.

Figure 8-39 Tinea versicolor. A and B, Multiple oval patches are seen in a guttate or raindrop pattern over the upper chest and back of two patients. C, In areas not exposed to sunlight, lesions are darker than surrounding skin, whereas in A and B sun-exposed lesions fail to tan, remaining lighter than surrounding skin.

(Courtesy Michael Sherlock, MD, Lutherville, Md.)

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).

Figure 8-40 Positive KOH preparation for tinea versicolor. The combination of hyphal and yeast forms of the fungus simulates the appearance of spaghetti and meatballs.

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.

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.

Figure 8-41 Irritant or ammoniacal diaper dermatitis. Note the erythema and scaling involving the convex surfaces and sparing of the intertriginous creases.

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.

Figure 8-42 Candidal diaper dermatitis. A and B, The eruption is bright red with numerous pinpoint satellite papules and pustules. Intertriginous areas are prominently involved.

Figure 8-43 KOH preparation of skin scrapings from an infant with candidal diaper dermatitis demonstrating pseudohyphae and spores.

Staphylococcal Diaper Dermatitis

Irritant diaper dermatitis is frequently complicated by secondary staphylococcal infection, or pustules may appear as primary lesions, especially in the first few weeks of life. The presence of thin-walled pustules on an erythematous base (larger than those seen with candidiasis) alert the clinician to the diagnosis. Typically, these rupture rapidly and dry, producing a collarette of scaling around the denuded red base (Fig. 8-44). A Gram stain of pustule contents demonstrates neutrophils and clusters of gram-positive cocci. Bacterial cultures are confirmatory but are rarely necessary. Early diagnosis and treatment with oral and topical antibiotics result in rapid resolution.

Figure 8-44 Staphylococcal diaper dermatitis. Numerous thin-walled pustules are surrounded by erythematous halos, as well as multiple areas in which pustules have ruptured, leaving a collarette of scale around a denuded erythematous base.

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.

Figure 8-45 Psoriatic diaper dermatitis. A, This child had a persistent diaper rash that did not respond to routine therapy. Note that scaling is not as intense as in psoriatic lesions seen elsewhere on the body. B, Another infant with inverse psoriasis involving the inguinal creases had also failed to improve despite multiple courses of topical antifungal treatment.

Tinea Diaper Dermatitis

Although less common than the other dermatitides in the differential diagnosis of diaper dermatitis, tinea must be kept in mind when examining a scaly perineal rash. Its characteristic features are those of a recalcitrant scaly eruption with an elevated or “active” scaly border (Fig. 8-46), from which scales can be scraped and tinea demonstrated on KOH preparation. It responds well to topical antifungals alone and should not be treated with topical steroids.

Figure 8-46 Tinea diaper dermatitis. Note the prominent scaling and the elevated active border.

Lichen Planus

Lichen planus is the prototypic lichenoid inflammatory eruption in that it displays flat-topped pruritic polygonal violaceous papules and plaques, which have a fine lacy pattern (Wickham striae) over their outer surfaces. They are often noted first over the dorsal surfaces of the extremities and can display koebnerization at sites of prior trauma (Fig. 8-47). The disorder may involve the nails (leading to dystrophy) as well as the oral mucosa, where lesions appear as lacy white plaques. Topical steroids are the mainstay of initial treatment. After resolution of primary lesions, a prolonged period of postinflammatory hyperpigmentation can be expected (see Fig. 8-124).

Figure 8-47 Lichen planus. These flat-topped violaceous papules of varying sizes and shapes overlying the anterior shin are typical. Note the linear lesions that formed after scratching, examples of the Koebner phenomenon.

Lichen Striatus

Lichen striatus is one of the more common and distinctive lichenoid papulosquamous eruptions. Lesions consisting of flat-topped papules appear fairly abruptly, usually in a linear or sometimes swirled distribution along the lines of Blaschko. Although they may involve any portion of the skin, they are more typically located on the extremities, neck, or upper back. They may be slightly erythematous or hypopigmented, and their surfaces are covered with fine scale (Fig. 8-48, A and B). When lesions form on a digit, lichen striatus can lead to temporary linear nail dystrophy. The cause of this otherwise asymptomatic disorder, which has its peak incidence in school-age children, is unknown. Spontaneous resolution within 1 to 3 years is the norm.

Figure 8-48 Lichen striatus. A, In this school-age child, mildly erythematous scaly flat-topped papules are seen in a linear distribution on the lower leg. B, Another child with darker skin has lesions that are hypopigmented on the posterior thigh.

(A, From Cohen BA: Atlas of pediatric dermatology, London, 1993, Mosby-Wolfe; B, from Cohen BA: Pediatric dermatology, ed 2, London, 1999, Mosby.)

Blistering Distal Dactylitis

Blistering distal dactylitis is a superficial bacterial infection involving the tips of the pads of fingers or toes. Lesions consist of tense blisters 0.5 to 1 cm in diameter that are filled with thin purulent fluid and surrounded by a narrow erythematous rim. With evolution, they may coalesce and extend proximally along the lateral aspect of the nail fold. On rupture, a thick crust forms (Fig. 8-50). Group A β-streptococci are the usual causative organisms and are detected by Gram stain and culture of vesicular fluid. On occasion, group B streptococci and S. aureus are isolated. The disorder can be distinguished from a paronychia by the distal location of initial lesions; from a herpetic whitlow by the larger size of the initial vesicles and Gram stain of the purulent fluid; and from burns by the purulence of the vesicular fluid and Gram stain revealing white blood cells and bacteria.

Figure 8-50 Blistering distal dactylitis. A tense blister filled with purulent fluid first developed at the tip of the thumb pad of this child. Subsequently, the lesion ruptured and crusted and newer lesions formed more proximally along the nail fold and at the tip of the index finger.

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