[Urticaria paradoxically aggraved by H1 antihistamines]. / Urticaires paradoxalement aggravées par les antihistaminiques H1.

BACKGROUND: H1 antihistamines (anti-H1) are the treatment of choice in chronic urticaria. We report five cases of urticaria, induced or aggravated by H1 antihistamines. METHODS: The immunoallergological investigations included prick-tests and intradermal tests with the antihistamine responsible for acute urticaria. RESULTS: The skin tests confirmed the non-IgE dependent nature of the urticarial eruptions and anti-leukotrienes (montelukast, Singulair) were effective in controlling chronic urticaria in 3/4 patients. DISCUSSION: Two hypotheses are discussed to explain the paradoxical aggravating effect of H1 antihistamines on the urticaria: 1) the patients are sensitive to the toxic, pro-inflammatory effect of the drug, which is the source of nonspecific activation of mast cells; 2) the fact that the urticaria is sensitive to anti-leukotrienes suggests that histamine is not the principal mediator of urticaria in these patients.

[Vaccine-induced urticaria: how to differentiate allergy (IgE) from pseudoallergy?]. / Urticaire après vaccination. Comment différencier allergie vraie (IgE dépendante) et pseudo-allergie?

BACKGROUND: The occurrence of allergic-type manifestations during the course of vaccination is relatively common, and in the majority of cases, these are benign reactions which are also known as "pseudoallergy". They are not immunological in nature and do not activate the effectors of specific immunity. OBJECTIVE: The aim of our work was to propose a practical diagnostic approach following an immediate and/or accelerated post-vaccination accident. PATIENTS AND METHODS: We report our experience in four adults who were referred for urticaria which appeared following vaccination and in two children who were allergic to eggs and were referred for assessment before administration of vaccines containing egg proteins. RESULTS: The immunoallergological examinations (prick-test and intradermal tests with immediate reading) confirmed the absence of immediate hypersensitivity to the vaccine in question and all the patients could be vaccined without incident. CONCLUSION: The majority of post-vaccination reactions with an allergic appearance is benign and do not contra-indicate further vaccination. If there is a suspicion of a true IgE dependent allergy, an immunoallergological investigation will differentiate true allergy from pseudoallergy.

[Immediate hypersensitivity is rarely implicated in drug induced urticaria]. / L'hypersensibilité immédiate est rarement en cause dans les urticaires médicamenteuses.

INTRODUCTION: The unexpected appearance of acute urticaria during the course of drug treatment gives rise to the following question: is it an allergic urticaria (due to an immediate hypersensitivity: IgE mediated specific immunity) or is it pseudo-allergic? We report our findings in an immuno-allergological study of patients who were sent for drug intolerance which presented as immediate hypersensivity (urticaria, angiooedema, anaphylactic shock). METHODS: A prospective study was conducted including all the patients who were sent to the unit for urticaria or angiooedema type drug intolerance. Patients were questioned about previous chronic urticaria and also about urticaria after taking different medicines. The clinical examination looked for a dermographism. All the patients then took skin tests for immediate hypersensitivity, the molecule was contra-indicated and tests for cross-reactivity were conducted. PATIENTS: Three hundred fifty patients were sent to this unit between February 2000 and April 2001 for drug intolerance, mostly with urticaria/angiooedema but in 7 cases with anaphylactic shock. The incriminated drugs were varied: 50 p. 100 were due mainly to penicillins and cephalosporins. Other drug groups were also involved: non steroid anti-inflammatories, aspirin and paracetamol for the most part, along with local anesthetics, morphine-based products, contrast iodine products, corticosteroids. RESULTS: Of the 350 patients tested, only 22 were allergic and had positive tests for the incriminated drug. In these 22 patients, with the exception of 2 of them, the effects were severe (anaphylactic shock in 7 patients) and the urticaria was only a minor manifestation of the reaction. The drugs responsible were cephalosporin (10 patients), the penicillin (6 patients), insulin (2 patients), gonadorelin (1 patient), carboxymethylcellulose (1 patient), lidocain (1 patient), and sulfamethoxazole (1 patient). The 328 other patients had negative tests and were able to retake the tested molecule without incident. Most of them had antecedents of chronic urticaria or dermographism. DISCUSSION: Only 22 patients of the 350, i.e. 6 p. 100 were genuinely allergic. These patients were those who presented the most severe symptoms. The other patients, i.e. the majority, suffered from pseudo-allergic drug-induced urticaria, which made retaking the medicines possible.