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Excerpt from Urticaria, Contact SyndromeSynonyms, Key Words, and Related Terms: CUS, nonimmunological contact urticaria, immunologic contact urticaria, NICU, immunological contact urticaria, immunologic contact urticaria, ICU, latex allergy Please click here to view the full topic text: Urticaria, Contact SyndromeBackground: Maibach and Johnson defined contact urticaria syndrome (CUS) in 1975; since then, numerous reports of CUS caused by a variety of compounds, such as foods, preservatives, fragrances, plant and animal products, and metals, continue to be reported. Because the exposure to contact urticariants can be similar to contact irritants (eg, health care workplaces), vigilance is required to ensure that the patient is properly investigated and diagnosed because contact urticaria in the setting of hand eczema may be overlooked.Pathophysiology: CUS can be described in 2 broad categories: nonimmunologic contact urticaria (NICU) and immunologic contact urticaria (ICU). The former does not require presensitization of the patient's immune system to an allergen, whereas the latter does. However, some contact urticaria reactions of unknown mechanism are unclassified, such as that for ammonium persulfate. NICU is the most frequent immediate contact reaction and occurs without prior sensitization in most individuals who are exposed. The symptoms may vary according to the site of exposure, the concentration, the vehicle, the mode of exposure, and the substance itself. The mechanism of NICU is incompletely understood. Previously, histamine was assumed to be released from mast cells in response to exposure to an eliciting substance. However, evidence exists that NICU may be mediated by prostaglandins. ICU is less frequent in clinical practice than NICU. ICU is a type 1 hypersensitivity reaction mediated by immunoglobulin E (IgE) antibodies specific to the eliciting substance. Therefore, prior immune (IgE) sensitization is required for this type of contact urticaria. Sensitization can be at the cutaneous level, but it may also be via the mucous membranes, such as in the respiratory or gastrointestinal tracts. The latter 2 routes of sensitization have frequently been reported among patients with ICU to latex. Persons with atopic dermatitis are predisposed toward ICU. In addition, it has been shown for ICU to latex that exposure through mucosa or dermatitic skin enhances the risk of developing immediate hypersensitivity. ICU reactions may spread beyond the site of contact and progress to generalized urticaria. When more severe, ICU may lead to anaphylactic shock. One such example is ICU from natural rubber latex. Typically, latex gloves cause a wheal and flare reaction at the site of contact. This reaction can affect either the person wearing the gloves or the person being touched by the person wearing the gloves. In addition to direct skin contact, allergy may be caused by airborne natural rubber latex. Thus, sensitized, yet undiagnosed, individuals are at risk when in contact with airborne ICU allergens. Cross allergy can also induce ICU reactions. The patient may be sensitized to 1 protein and react to other proteins that contain the same or similar allergenic molecules. In the example of latex allergy, patients may experience symptoms from banana, chestnut, and avocado, as well as a number of other fruits, vegetables, and nuts. This phenomenon places patients with ICU at further risk. Both ICU and NICU can display site specificity; for example, the neck and perioral areas are more sensitive than the forearm. This finding can be important in diagnostic testing. Frequency:
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