[New pathophysiological concepts on aspirin hypersensitivity (Widal syndrome); diagnostic and therapeutic consequences].

Hypersensitivity to aspirin usually takes the form of a clinical syndrome combining chronic rhinitis, nasal polyposis and asthma attacks that are exacerbated by aspirin or other non steroidal anti-inflammatory drugs (NSAIDs). This syndrome, first described by Widal in 1922, is very frequent: it affects nearly 15% of asthmatic patients and is usually associated with severe and sometimes fatal asthma. In other instances, hypersensitivity to NSAIDs manifests in the form of skin lesions, such as urticaria and angioedema. Until recently, the pathophysiological mechanism of NSAID hypersensitivity was somewhat mysterious. The fact that the main mediators involved are sulfidoleukotrienes (LTC4, LTD4, LTE4) and that the drugs responsible all inhibit cyclooxygenase-1 (COX-1), pointed to a pharmacogenetic abnormality of arachidonic acid metabolism. An immunopharmacological study of basophil activation (detected by flow cytometry), sulfidoleukotriene production in the presence of NSAIDs in vitro, and other related studies reviewed here have revealed that: a) basophils from patients with the Widal syndrome are hyperactivated in a non specific manner, probably related to chronic inflammation in the skin or airways; b) these hyperactive basophils produce increased amounts of sulfidoleukotrienes but decreased amounts of PGE2 when exposed to NSAIDs in vitro. These observations led to the development of an in vitro diagnostic test which, in many cases, can replace challenge tests. The pathogenic mechanism of the Widal syndrome now appears to involve the combined effects of chronic inflammation (causing non specific cellular hyper-reactivity, particularly of mast cells, basophils and eosinophils) and a pharmacogenetic abnormality of arachidonic acid metabolism in response to NSAIDs. This leads to sulfidoleukotriene overproduction and to a decrease in the anti-inflammatory prostaglandin PGE2. This concept is compatible with the onset and outcome of most cases of the Widal syndrome, and provides a therapeutic rationale.