A new review published in the Journal of Asthma and Allergy assessed the diagnostic and treatment approaches to aquagenic urticaria (AU), a difficult to treat, rare form of urticaria triggered when skin is exposed to water, including sweat and tears.

The lack of a clear pathogenesis for AU has contributed to difficulty in proposing evidence-based treatments for affected patients. The mechanism of AU is not well understood and researchers have been unable to ascertain whether the condition is dependent on histamine release or not.

The clinical presentation of AU entails “characteristic 1–3mm folliculocentric wheals and surrounding 1–3cm erythematous flares within 20–30 minutes following skin contact with water.” The review states how diagnosis is based on a history of urticaria after water exposure and a positive water challenge test. 

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The main challenge in diagnosing AU is in differentiating the condition from other types of physical urticaria. Lab tests can be used in this regard to rule out other reactions, such as immunoglobulin E-mediated allergic reaction, however the histopathology of AU is consistent with nonspecific urticaria, so it will not aid in diagnosis.

Generally, oral H1 antihistamines are used as first-line therapy. Oil in-in-water emulsions and petrolatum-containing creams applied prior to water exposure have been shown to be effective in reducing urticaria in some AU patients. This option should be considered and tried before antihistamines, particularly in pediatric patients, to side-step the possible adverse effects of oral antihistamines.

If topical and oral treatments are inadequate, Psoralens ultraviolet radiation A and ultraviolet radiation B have been reported to resolve symptoms of AU in a few cases (Parker RK, Crowe MJ, Guin JD. Aquagenic urticaria. Cutis. 1992;50(4):283–284). Psoralens ultraviolet radiation A has also been used in combination with antihistamine therapy with good response (Martínez-Escribano JA, et al. Treatment of aquagenic urticaria with PUVA and astemizole. J Am Acad Dermatol. 1997;36(1):118–119).

The authors conclude that the cornerstone of therapy for AU is nonsedating, second-generation H1 antihistamines; evidence for the use of other therapies (other oral agents, topical agents, and phototherapy) are currently lacking and require further investigation. The authors also speculate that genetic linkage studies may be of benefit in uncovering the pathogenesis of AU.

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