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Contact Dermatitis Diagnosis and Management: When to Refer for Patch Testing

Contact Dermatitis Diagnosis and Management: When to Refer for Patch Testing

Contact dermatitis (CD) is a relatively common inflammatory skin condition, grouped with occupational skin disease. CD usually presents with erythematous and pruritic skin lesions that develop after contact with a foreign substance. There are two types of CD: irritant CD (ICD) and allergic CD (ACD). The most common substances that are known to cause CD are nickel, poison ivy, and fragrances.

ICD is due to irritation of the skin caused by a particular substance and is a non–immune-mediated reaction; it is caused by cytotoxic effects of cutaneous inflammation of the skin. Common symptoms are pruritus, burning, and pain, which usually occur immediately after contact with the offending agent and may continue to persist if the irritant chemical is not recognized. The skin is usually dry and fissured, and borders of the lesion are not always distinct. Some examples of ICD include diaper dermatitis and excessive lip licking causing perioral dermatitis. Chemical irritants such as solvents and cutting fluids account for many causes of occupational skin disease.

ACD, by contrast, is a delayed hypersensitivity reaction in which a foreign substance meets the skin. Skin reactions and changes occur upon re-exposure to the offending substance when antigen-specific T cells are activated after someone has become sensitized. ACD is an example of a type IV, delayed-type hypersensitivity reaction. Location of ACD is usually on exposed areas of the skin and/or where the chemical encounters skin. Pruritus, which can often be severe, is the dominant symptom, but other symptoms involve erythema, vesicles, bullae, and chronic lesions which can lead to lichenification, cracks, and fissures. Borders of lesions are often distinct. An example of ACD is exposure to urushiol, the substance that causes dermatitis related to poison ivy, oak, or sumac. Another example is ACD caused by metals in jewelry or metal belt buckles. It is important to note that many patients can have a mix of ICD and ACD.

The most common causes of ACD are exposure to nickel (14.3%), fragrance mix (14%), neomycin (11.6%), balsam of Peru (10.4%), and thimerosal (10.4%). Nickel is a component of many types of jewelry, electronic devices such as cell phones, clothing, and tools such as scissors. Fragrance mix is a combination of several chemicals known to cause ACD, and can be found in cosmetics, shampoos, soaps, moisturizers, and other toiletry products. Balsam of Peru is a fragrance used in many cosmetic products and is actually used as a "fragrance masker" in products that are labeled "unscented"—no scent is perceived by the consumer, but the chemical is still present in the product and being applied to the skin. Neomycin is found in over the counter topical antibiotics, and thimerosal is used as a topical disinfectant and preservative in various medicinal products.

Diagnosis of CD is often clinical and based on history and physical exam. If a causative substance is known or strongly suspected, the first step in management is to avoid the substance and confirm the diagnosis if the symptoms resolve. Management of acute flares with topical corticosteroids such as triamcinolone or clobetasol can be very helpful. Antihistamines are generally not helpful at controlling itch in CD. However, sedating antihistamines such as diphenhydramine or hydroxyzine can offer some relief.

If avoidance of the potential trigger and empiric treatment do not relieve symptoms, patch testing may be indicated. Patch testing attempts to recreate an allergic reaction to allergens to confirm or rule out potential triggers. One indication for patch testing includes patients with distributions that are highly suggestive of ACD, such as involvement of the hands, feet, face, or eyelids. If there is unilateral involvement, ACD should also be suspected, and therefore patch testing is indicated. Further, if a patient has a clinical history highly suggestive of ACD, patch testing should be performed. Patch testing should also be performed on patients that are in high-risk occupations for ACD, including healthcare workers, cosmetologists, and machinists. If dermatitis remains uncontrolled or unresponsive to treatment, or there is worsening of dermatitis that was previously controlled, patch testing should be considered. It is important to note that ACD can occur in response to topical medical treatments. If a patient is using a topical product for atopic dermatitis, psoriasis, or other skin problem, and develops a dermatitis at that location, then patch testing should be performed.

Patients should be referred to an allergist to discuss the appropriate panel(s) for testing and protocols for performing patch testing correctly. Many dermatologists also perform patch testing. There are various panels that can be done, including T.R.U.E. Test with 36 allergens and the North American Comprehensive Series with 80 allergens. Patch testing is typically completed on intact skin (usually the back) and occluded for 2 days. Readings of patch tests are typically performed at 48 hours, with another delayed reading at 72 to 96 hours or later. While non-irritating concentrations have been established to provide accurate results, unfortunately patch testing only has sensitivity and specificity of 70% to 80%. Once patch testing is completed, patients can be educated to avoid potential triggers and monitored for improvement in their dermatitis.

References
  • Mowad CM, et al. Allergic contact dermatitis: Patient diagnosis and evaluation. J Am Acad Dermatol. 2016;74:1029-1040.
  • Usatine RP, Riojas M. Diagnosis and management of contact dermatitis. Am Fam Phys. 2010;82:249-255.

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Filed under: Allergy/Immunology

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