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July 2007 QUIZ OF THE MONTH . . .
There is a continuing intensive investigation of pathogenic mechanisms and therapy of atopic dermatitis (AD). Which of the statements below about AD are true or false?
- AD occurs in about 2% of all children in the USA
- Sensitization to food and/or inhalant allergens is present in about 75% of children with AD
- Histologic studies of clinically unaffected skin in AD patients show no abnormalities
- Staphylococci are present in AD skin lesions but do not appear to play a pathogenic role
- Topical application of calcineurin inhibitors can allow reduction in the use of topical corticosteroids in AD
Discussion
AD is a common disorder, occurring in 10-20% of children and about 2% of adults in the USA. AD has been classified as either 1) "extrinsic" (about 70-80% of AD cases in children) in which the serum levels of total IgE and IgE antibodies against certain foods and inhalants are increased or 2) "intrinsic" in which the serum levels and allergen-specific IgE are not increased. However, there is evidence of a Th2 immune response in both the extrinsic and intrinsic types manifest as eosinophilia and increased IL-13 levels. Biopsies of clinically uninvolved skin in AD patients frequently show evidence of such a Th2 immune response. In chronic AD skin lesions there is evidence suggesting participation by both Th1 and Th2 immune responses. In newly appearing eczematous lesions resembling AD in adults, one must rule out mycosis fungoides, an expression of a cutaneous T cell lymphoma.
Staph aureus frequently infects AD lesions. By one or more of several mechanisms this Staph infection aggravates the AD. Therapeutic reduction of the Staph colonization of AD lesions frequently leads to significant improvement in the AD.
A major breakthrough in the pharmacotherapy of AD has been the topical application of calcineurin inhibitors such as tacrolimus or pimecrolimus. This therapy is frequently at least as effective as low potency topical corticosteroids. Topical tacrolimus therapy has been shown to allow control of AD with lower doses (or even no doses) of potent topical corticosteroids. A concern has been raised in the FDA about the oncogenic potential of long-term topical calcineurin inhibitors. Many experts in AD have feel that this potential hazard is overstated. However, they have generally gone along with the current stipulation that topical calcineurin inhibitor therapy should not be the first-line therapy of AD at this time.
References
1. Curr Allergy and Asthma Reports 2006;6:384-89
2. Curr Allergy and Asthma Reports 2006;6:275-81
3. J Allergy Clin Immunol 2006;118:152-69
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