A 1-year-old Asian American girl is brought to her family physician for a new rash on her face and legs (Figures 151-1 and 151-2). The child is scratching both areas but is otherwise healthy. There is a family history of asthma, allergic rhinitis, and atopic dermatitis (AD) on the father's side. The child responded well to low-dose topical corticosteroids and emollients.
Atopic dermatitis on the cheeks of an infant. (Reproduced with permission from Milgrom EC, Usatine RP, Tan RA, et al: Practical Allergy. Philadelphia, PA: Elsevier; 2004.)
Atopic dermatitis on the leg of the infant in Figure 151-1. The coinlike pattern is that of nummular eczema. (Reproduced with permission from Milgrom EC, Usatine RP, Tan RA, et al: Practical Allergy. Philadelphia, PA: Elsevier; 2004.)
AD is a chronic and relapsing inflammatory skin disorder characterized by itching and inflamed skin that is triggered by the interplay of genetic, immunologic, and environmental factors.
AD is the most frequent inflammatory skin disorder in the United States and the most common skin condition in children.1
Worldwide prevalence in children is 15% to 20% and is increasing in industrialized nations.2
Sixty percent of cases begin during the first year of life and 90% by 5 years of age.1 One third will persist into adulthood.2
Sixty percent of adults with AD have children with AD (Figure 151-3).1
It is estimated that 2% to 3% of the adult population is affected.3
The child and his mother both have atopic dermatitis, but not in the most typical distribution. (Reproduced with permission from Richard P. Usatine, MD.)
ETIOLOGY AND PATHOPHYSIOLOGY
Strong familial tendency, especially if atopy is inherited from the maternal side.
Associated with elevated T-helper (Th) 2 cytokine response, elevated serum immunoglobulin (Ig) E, hyperstimulatory Langerhans cells, defective cell-mediated immunity, and loss of function mutation in filaggrin, an epidermal barrier protein.
Exotoxins of Staphylococcus aureus act as superantigens and stimulate activation of T cells and macrophages, worsening AD without actually showing signs of superinfection. This bacterium has been found on more than 90% of adults with the disease, and only 5% of nonaffected adults.4
Patients may have a primary T-cell defect. This may be why they can get more severe skin infections caused by herpes simplex virus (eczema herpeticum as seen in Figure 151-4) ...