Dermatite allergica da contatto da corticosteroidi: procedimento diagnostico

It's well known that topical corticosteroids (TC), compounds equipped with marked anti-inflammatory, immunosuppressive and antiproliferative effects, are able to induce allergic contact dermatitis (ACD). Its prevalence is very variable, being estimated between 0.2% and 5% in consecutive patch-tested subjects for contact dermatitis. Clinical diagnosis is not always easy; this aspect, together with the risk of adverse reactions following systemic administration to such compounds in individuals sensitized to one or more CT and the need to identify alternative compounds, makes necessary the adoption of a diagnostic tool. This provides for the sequential performance of patch test and, if negative, prick test, and when also the latter is negative, intradermal test with the suspected CT and a series of structurally diverse CT in order to identify possible cross-reactions. The choice of the optimal vehicle for patch testing is not always easy. Vaseline is the optimal vehicle for budesonide and for most of the CT, while ethanol is the choice vehicle for some CT, such as hydrocortisone 17-butyrate. Use concentration acts in a manner inversely proportional to the diagnostic value of patch test: there is a high risk of false negative reactions if concentration is too high. I this case the anti-inflammatory effect is prevalent. This anti-inflammatory action significantly influences the time reading of patch test. For this reason it is essential that the patch test readings are carried out until the seventh day, also to avoid the "skin blanching" and "'edge effects", typical of the readings done in the first-second day. Skin prick test and intradermal test ensure greater bioavailability of the drug but they can cause local and systemic side effects. Moreover, intradermal test can be set-up and done only if CT is water-soluble. In case of negative results of patch, prick and intradermal test, it is advisable to perform ROAT (Repeated Open Application Test). The author discusses the advantages and limits of these diagnostic tools, specifying optimal concentration and vehicles for epicutaneous tests and stating methods to evaluate the results.