Pediatric Atopic Dermatitis Workup

Updated: Mar 13, 2019
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

No definitive laboratory tests are used to diagnose atopic dermatitis (AD). Elevated serum immunoglobulin E (IgE) levels and peripheral blood eosinophilia occur in most individuals with atopic dermatitis, and these findings may be useful in confirming the atopic status of suspected cases. The presence of serum IgE directed against the cell wall of S aureus is observed in hyper-IgE syndrome and atopic dermatitis.

Common infections that mimic or complicate atopic dermatitis can be tested for as follows: conduct a Tzanck smear for herpes simplex virus (HSV), a potassium hydroxide (KOH) preparation for dermatophytes, and a Gram stain for bacterial infections.

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Other Tests

Prick skin testing to common allergens can help identify specific triggers of atopic dermatitis. For accuracy, antihistamines must be discontinued for 1 week and topical steroids for 2 weeks prior to testing. Although skin tests are used most often in young children with moderate-to-severe disease, false-negative and false-positive test results are not uncommon in children younger than 8 years. If positive, these tests do not necessarily indicate clinically significant triggers. Prick skin tests only indicate that the patient has been sensitized to particular antigens. For example, most children shown to have multiple food allergies by skin tests only demonstrate clinically detectable allergic reactions to 3 or fewer foods when tested by double-blind randomized provocative testing.

Radioallergosorbent test (RAST) and enzyme-linked immunosorbent assay (ELISA) in vitro tests identify serum IgE directed toward specific allergens (allergen-specific IgE). As with prick skin tests, these diagnostic methods show a poor predictive value for clinically significant food allergies and may produce false-positive results when the patient's serum contains elevated nonspecific (or total) IgE levels.

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Histologic Findings

Acute eczematous lesions show histologic markings of hyperkeratosis, parakeratosis, and acanthosis with a decreased or absent granular cell layer.

Important features in histologic diagnosis include spongiosis (accumulation of fluid in the intercellular and intracellular areas) and exocytosis (infiltration of leukocytes through the epidermis).

Chronic eczematous lesions display hyperkeratosis with areas of parakeratosis and papillomatosis (upward proliferation of dermal papillae).

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