Delayed-type hypersensitivity (type IV) reactions in dental anesthesia

The recommended methodology of evaluating patients who have presented with reactions to local anesthetics consists of epicutaneous skin testing and serial subcutaneous challenge. However, the role of type IV reactions in this group has been poorly documented. Epicutaneous routine testing and subcutaneous challenge to local anesthetic was performed, as well as patch testing and subcutaneous rechallenge of both at 24 and 48 hours with evaluation up to 72 hours was performed. Three patients presented with a history of localized edema after dental anesthesia. All had negative lidocaine and mepivacaine testing as well as negative lidocaine challenge on evaluation at 1 hour. The first patient, who had previously reacted to EMLA, reacted to both lidocaine and mepivacaine patch testing and challenge, with delayed swelling at 24 and 48 hours after challenge. This patient subsequently tolerated the ester anesthetic chloroprocaine. Two other patients had strong histories of contact dermatitis. Patch testing and challenge with lidocaine was negative, but strong reactions were found to benzocaine on patch testing. Patients undergoing local anesthetic testing should be screened historically for features and riskfactors associated with type IV reactions. This should be considered in patients who react to multiple amide anesthetics, who have delayed swelling, or who have a history of severe contact dermatitis. We confirm previous data showing that patients reacting to benzocaine can tolerate lidocaine and that lidocaine-allergic individuals can tolerate ester anesthetics.