[Does hypersensitivity to multiple drugs really exist?]

Multiple-drug hypersensitivity (MDH) in the literature concerns different entities. Our objective was to define its frequency and characteristics in patients examined for cutaneous adverse drug reaction (CADR) before studying genetic predisposition.

From a database comprising all patients referred for CADR between 2000 and 2010, we selected those meeting the following criteria: sensitisation to at least two chemically unrelated substances, as confirmed by positive skin tests or challenge tests. The following were excluded: patients with haematological diseases, HIV or chronic wounds and sensitization to the excipients.

Of the 1925 patients included, 11 (0.6%) were classed as polysensitized: eight women and three men, of mean age 62 years, presenting 2.5 episodes of drug hypersensitivity per patient. Four cases of DRESS were noted.

The strict criteria stipulated for this study enabled us to select patients with MDH, and to affirm that while it does in fact exist, it seems rare. Compared to polysensitized patients described in the literature, we preferred to distinguish between three groups of MDH: one occurring with different substances in separate episodes of CADR, one occurring with different substances during the same episode of CADR, and one occurring during DRESS and correlating with viral replication.

MDH exists and genetic predisposition could be investigated by studying cytokine polymorphism in such patients. However, because of its rarity, it is impossible to rule out fortuitous association of two episodes of CADR in the same patient.