Pediatric Contact Dermatitis Workup

Updated: Jan 08, 2019
  • Author: Nanette B Silverberg, MD; Chief Editor: Dirk M Elston, MD  more...
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Workup

Approach Considerations

Patch testing may suggest or confirm the etiologic agent in allergic contact dermatitis. [22, 23, 24] Laboratory studies are generally of little value in proving a diagnosis of contact dermatitis. However, they may be of value in eliminating some disorders from the differential diagnosis.

Go to Irritant Contact Dermatitis, Allergic Contact Dermatitis, and Protein Contact Dermatitis for complete information on these topics.

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Patch Testing

By placing standard concentrations of common allergens or specific ingredients of an implicated product on the skin and leaving them covered for 2 days, one may identify the allergen. If the patient has been previously sensitized to one of the agents under occlusion, this reexposure produces the elicitation phase of a type IV hypersensitivity reaction resulting in pruritus, erythema, and vesiculation. There are a variety of panels that are used in patch testing, including the True Test and the North American Contact Dermatitis Series; however, because of the small size of a child's back, small or limited panels based on suspected agents are often used.

Anaphylaxis may occur shortly after application of antigens used in patch testing. This finding is particularly true when testing for latex allergy but may occur with exposure to other antigens. 

Monitor patients for anaphylactic reactions to antigens used in patch testing. Appropriate resuscitation must be available should anaphylaxis occur during the early stages of patch testing. Patch testing is contraindicated in the setting of angioedema and/or contact-induced anaphylaxis and should be avoided in patients with contact urticaria.

Atopic patients are more susceptible to irritant patch test reactions, especially when testing with metals. This may lead to false-positive results from routine patch testing. In a study of 101 sets of twins, no correlation was found between positive patch test results and atopy.

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Dimethylgloxime (DMG) Spot Test

For patients with nickel allergy, a simple procedure exists to test jewelry for the presence of nickel. Trace amounts of nickel can be detected using the dimethylgloxime (DMG) spot test.

Two or 3 drops of 1% DMG and 10% hydroxide solution are placed on a white cotton-tipped applicator. The applicator tip is then rubbed against metallic areas of the jewelry. The appearance of a pink color on the applicator tip is a positive result and proof of the presence of nickel. This test is nondestructive. DMG test kits are inexpensive and available from many medical supply stores.

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Biopsy

Biopsies are of little diagnostic help in contact dermatitis. Most types of contact dermatitis show very similar pathologic changes, and allergic and irritant contact dermatitis may not be distinguished with certainty in all cases. However, skin biopsy findings may serve to eliminate some conditions included in the differential diagnosis.

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Histologic Findings

Histologic findings in contact dermatitis are not usually helpful in identifying the specific cause of the contact dermatitis. Findings in acute contact dermatitis include intercellular edema in the epidermis and vesiculation or blister formation.

Mast cells may be increased in urticarial reactions.

Chronic contact dermatitis shows signs of lichenification and varying degrees of nonspecific inflammation.

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