Protein Contact Dermatitis Workup
- Author: Cheryl Levin, MD; Chief Editor: Dirk M Elston, MD more...
The most sensitive methods for detecting protein contact dermatitis include prick and scratch tests, although open application testing may also be performed. Patch-test results are usually negative.
Systemic symptoms, including anaphylaxis, have been reported with prick and scratch tests. Therefore, these tests should be performed only in settings where appropriate resuscitation equipment is available.
Testing should be performed to exclude a tinea infection. This may consist of potassium hydroxide (KOH) testing, fungal culture, or periodic acid-Schiff staining
Open Application Testing
Open application testing involves placing or rubbing the allergen on intact skin and/or damaged, eczematous skin.
Prick testing involves placing one drop of diluted test allergen, vehicle (negative control), and histamine (positive control) onto the volar forearm of the patient. The test sites are pierced with lancets to introduce the allergen into the dermis. The results are read at 15-minute intervals over 1 hour. A positive reaction is a wheal of at least 3 mm in diameter that is also at least half the size of the histamine control in the absence of a reaction in the vehicle control.
Scratch testing involves placing one drop of diluted test allergen, vehicle, and histamine onto the volar forearm and scratching the skin lightly with a needle. The test sites are read at 15-minute intervals over 1 hour. A positive reaction is a wheal that is at least half the diameter of the histamine control in the absence of a reaction in the vehicle control.
A radioallergosorbent test (RAST) with a particular allergen may be performed to measure allergen-specific IgE in the patient's serum, although a negative test result does not rule out protein contact dermatitis. RAST testing measures only circulating antibodies and does not assess tissue-bound antibodies.
If the patient is experiencing extracutaneous symptoms, appropriate imaging studies may be performed. No specific imaging study is required in the evaluation of protein contact dermatitis.
Histology findings are relatively nonspecific. Biopsy may reveal perivascular lymphocytic infiltrate with eosinophils or spongiosis with lymphocytic exocytosis.
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