[Allergic and pseudo-allergic reactions to foods in chronic urticaria].Ann Dermatol Venereol 2003; 130 Spec No 1:1S35-42AD
The fact that more than 30 p. 100 of patients with chronic urticaria incriminate foods, and that acute urticaria is a frequent symptom of food allergy, argue in favour of a systematic search for food involvement in chronic urticaria. A global overview of publications through Medline selects 49 out of 189 papers upon strict criteria, devoted to the links between chronic urticaria and foods. Possible links exist between chronic urticaria and intolerance to additives, intolerance or allergy to contaminants, pseudo-allergic reactions to foods and IgE-dependent food allergy. The diagnosis of intolerance to additives relies on double blind placebo-controlled oral challenges, showing positivity in 2 to 3 p. 100 of cases. Flavours are being suspected but have not been validated by such oral challenges. Contaminants are nickel salts, penicillin residues in meats and milk, Anisakis larvae in fish. Intolerance to biogenic amines could be somewhat frequent and is well-documented by experimental studies of the metabolism of histamine and by the results of specific diets with a low content of amines. IgE-dependent food allergy has been evidenced in 1 to 5 p. 100 of cases. The author puts forward a methodology to search for the implication of foods in chronic urticaria, restricting the search to non-inflammatory CU, discarding moreover chronic urticaria due to physical agents, or to contact. Idiopathic chronic urticaria, that might include a subgroup of auto-immune chronic urticaria is under scope. A preliminary study of the regimen during one week needs to be carried out in order to detect an excess of consumption of categories of foods inducing pseudo-allergic reactions, or of additives. An eviction diet for biogenic amines may be proposed first. Its failure may lead to skin prick tests to foods that are daily consumed. Biological tests are not advised. When sensitization is confirmed, a 3 week eviction of the food comes ahead of a double blind placebo-controlled oral challenge. The positivity indicates that this food is likely to be a causal agent and the diagnosis can finally be based on the recovery after the implementation of strict avoidance diets.