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.
Atopic dermatitis is a chronic, relapsing skin disease characterized by xerosis, pruritus, and characteristic skin findings. Thecondition 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 hypoand 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 (Fig. 190-1).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 riskfor infections with cutaneous viruses and can develop disseminated skin infections with viruses such as herpes simplexvirus (eczema herpeticum), varicella-zoster virus, smallpoxvirus (eczema vaccinatum), and molluscum contagiosum.Atopic skin is more susceptible to fungal infections as well.
Figure 190-1 Atopic dermatitis (arm).
Signs of concomitant infection include acute worsening ofdisease in an otherwise well-controlled patient, resistance tostandard therapy, fever, and presence of pustules, fissures, orexudative or crusted lesions (Fig. 190-2). Eczema herpeticumand eczema vaccinatum can be life threatening if not treated.
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.
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 dermatitisis different from that of atopic dermatitis, typically involvingthe 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.