A positive patch test indicates that the patient is sensitized to the tested allergen. Patch testing should be performed in a systematic fashion and include a delayed reading. Due to the overwhelming number of potential allergens a person can encounter daily, the pre-patch test, history-taking consultation should be streamlined yet broad many centers have a pre-test questionnaire that they include as part of the initial evaluation (see Table 2). Patch testing is the gold standard diagnostic test for confirming allergens to which an individual is sensitized. Improvement with time away from the activity where the allergen is contacted. A temporal association between exposure to an allergen source and flare of the dermatitis.ģ. Because ACD can spread from the point of contact, a full-body examination should be conducted before inferring the allergen based on the pattern of distribution. For example, dermatitis presenting at the earlobes may suggest contact allergy from an earring, whereas involvement of the bilateral lateral neck may indicate allergy secondary to a perfume. ![]() Anatomical predilection of the dermatitis for specific geographical areas or distinct linear or geometric shape, suggest the origin could be “an outside affair” (see Table 1). When to Investigate and Evaluate for ACDĪCD should be suspected in patients with the following profiles (see Flow Chart):ġ. Those suffering from ACD can reach remission with proper diagnostic testing and interpretation, leading to identification and avoidance of the culprit allergen. By connecting the history and clinical findings and evaluating the relevance of positive patch test findings, a diagnosis of ACD can be confirmed and allergen sources identified. Patch testing is therefore an important diagnostic tool used to identify potential allergens of contact sensitization. ![]() Given the numerous allergen sources and delayed dermatitis expression after allergen exposure, determination of the cause of ACD can be challenging by history alone. Atopic and irritant contact dermatitis can occur concurrently with ACD.<</p> 2 ACD can be acute, as seen in linear blisters secondary to poison ivy exposure, or chronic, secondary to a wide range of allergens from fragrances to nickel-releasing jewelry to sun-activated compounds. 1 The complex pathogenesis involves delayed type IV hypersensitivity with re-exposure to an allergen causing activation of TH1 cells and release of inflammatory cytokines in a previously sensitized individual. Allergic contact dermatitis (ACD) affects more than 13 million Americans annually.
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