and contact allergens, infections, irritants, extremes of temperature, sweat, and lack of humidity can exacerbate the condition, as can scratching or rubbing. Triggers are somewhat variable from individual to individual.
Epidemiology: Atopic dermatitis is the most common skin disease in children, with an estimated prevalence of up to 20% of children. Only 1% to 2% of adults manifest disease. In addition to genetic factors, an environmental influence contributes. Atopic dermatitis occurs more frequently in urban areas and in higher socioeconomic classes. Prevalence is lower in areas where industrial pollution is less and where eosinophil-mediated infections such as helminthic infections are endemic. Patients generally have a family history of atopy. Children with atopic dermatitis are predisposed to the development of allergy and allergic rhinitis, referred to as the atopic march. Asthma develops in up to half of children with atopic dermatitis, and allergic rhinitis even more frequently. Food allergies are commonly associated with atopic dermatitis.
Clinical Manifestations: Atopic dermatitis is a chronic, relapsing skin disease characterized by xerosis, pruritus, and characteristic skin findings. The condition generally improves with age and remits in adulthood, although some childhood cases will continue into adulthood. Characteristic lesions of atopic dermatitis are erythematous papules or plaques with ill-defined borders and overlying scale or hyperkeratosis. Lesions can be secondarily excoriated or have an overlying crust that is yellow or hemorrhagic. Weeping may be present in acute stages. Lichenification is found in
older lesions. Formation of fissures is common in both acute and chronic lesions. Temporary hypo- and hyperpigmentation can be seen after lesions resolve, but atopic dermatitis is not usually scarring unless secondary features become severe (e.g., infection or physical manipulation [scratching]).
Characteristic locations vary with the age of the patient. Infantile atopic dermatitis typically affects the face and extensor surfaces of the extremities and is often generalized. Childhood lesions predominate in flexural surfaces (antecubital and popliteal fossae), wrists, ankles, hands, and feet.
The adult phase occurs after puberty and manifests in the flexural areas including the neck, as well as predominant involvement on the face, dorsa of the hands, fingers and toes, and the upper arms and back. Secondary bacterial infection, most commonly with Staphylococcus aureus or less commonly with Streptococcus pyogenes, is frequently present. Patients are at increased risk for infections with cutaneous viruses and can develop disseminated skin infections with viruses such as herpes simplex
virus (eczema herpeticum), varicella-zoster virus, smallpox virus (eczema vaccinatum), and molluscum contagiosum. Atopic skin is more susceptible to fungal infections as well. Signs of concomitant infection include acute worsening of disease in an otherwise well-controlled patient, resistance to standard therapy, fever, and presence of pustules, fissures, or exudative or crusted lesions. Eczema herpeticum and eczema vaccinatum can be life threatening if not treated.
Laboratory and imaging studies: Diagnosis of atopic dermatitis is based on clinical signs and
symptoms. Skin biopsy findings are generally characteristic but not exclusively diagnostic and can overlap with other skin conditions. Peripheral blood eosinophilia and elevated IgE levels can be found but are not specific. Skin prick testing or measurement of specific IgE antibody levels can detect sensitization to food and environmental allergens, although false-positive findings occur.
Differential diagnosis: The differential diagnosis of atopic dermatitis is extensive, but the history of a relapsing pruritic condition in the setting of atopy and skin lesions in a characteristic distribution is typical. The lesions of seborrheic dermatitis have circumscribed and well-defined borders. The scale or hyperkeratosis is thicker, greasy, and yellowish. The distribution of seborrheic dermatitis is different from that of atopic dermatitis, typically involving the scalp, eyebrows, perinasal region, upper chest, and back. Occasionally the two conditions coexist. Psoriasis tends to localize on the elbows, knees, lower back, and scalp. The lesions of psoriasis on exposed surfaces are salmon color at the base with an overlying hyperkeratosis that is much thicker with silver coloration. They are generally very well demarcated, oval or round, thick plaques. Allergic contact dermatitis has a distribution limited to one area of the body corresponding to contact with the allergen. The lesions generally make bizarre, linear, square, or angulated shapes corresponding to the source. Nickel dermatitis is common and results from contact sensitization to nickel in metals. It occurs in characteristic locations, such as the periumbilical area (where metal from pant buttons rub against skin); on the ear lobule or neck (where earrings contact skin); circumferentially around the neck (necklaces); and under rings or wristbands. Patients with atopic dermatitis can have concomitant
contact dermatitis as well.
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