Continuing medical education
Allergic contact dermatitis: Patient diagnosis and evaluation

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Allergic contact dermatitis resulting from exposure to a chemical or chemicals is a common diagnosis in the dermatologist's office. We are exposed to hundreds of potential allergens daily. Patch testing is the criterion standard for diagnosing the causative allergens responsible for allergic contact dermatitis. Patch testing beyond standard trays is often needed to fully diagnose patients, but not all dermatology practices have access to this testing procedure or these allergens. In order to adequately evaluate patients, physicians must understand the pathophysiology of the disease process and be well versed in the proper evaluation of patients, indications for patch testing, proper testing procedure, and other diagnostic tools available and be aware of new and emerging allergens.

Section snippets

Pathophysiology: Basic science

ACD is a type IV, delayed-type reaction that is caused by skin contact with allergens that activate antigen-specific T cells in a sensitized individual. The sensitized T cells are primarily T-helper 1 (TH1) type. In the sensitization phase, innate immunity is activated through keratinocyte release of interleukin (IL)-1α, IL-1β, tumor necrosis factor–alpha, granulocyte-macrophage colony-stimulating factor, and ILs-8 and -18. Langerhans and dermal dendritic cells uptake the allergen and migrate

Indication for patch testing

Patch testing is the criterion standard in the diagnosis of ACD. Patch testing attempts to recreate, in vivo, an allergic reaction to nonirritating concentrations of an allergen that is suspended in a vehicle. The decision to perform patch testing and which allergens to test depends on many factors.

Some common indications for patch testing include: (1) distributions that are highly suggestive of ACD—for example, ACD of the hands, feet, face, and eyelid, as well as unilateral presentations; (2)

Supplies

In addition to allergens, other supplies required include tape, a refrigerator for storage of the allergens, chambers, A Wood's lamp, markers, and maps.

Patch tests are used to identify the cause of ACD and aim to reproduce an eczematous reaction to a causative allergen applied to intact skin. Closed patch testing involves the application of allergens under occlusion to the skin of the upper aspect of the back for a period of 2 days. Readings are generally performed at that time, with additional

New/emerging allergens

Advances in technology and the continually evolving nature of industry results in the introduction of many new chemicals into the environment and personal care products. This results in new consumer exposure and potential new allergens. The number of new products developed annually is substantial; the number of new allergens is sizeable. Clinicians must be aware that new, yet to be described allergens may be responsible for a patient's ACD. Only with investigative work by the patient,

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    Funding sources: None.

    Conflicts of interest: None declared.

    Date of release: June 2016

    Expiration date: June 2019

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