Delayed-type hypersensitivity to a nonionic, radiopaque contrast medium

Background True allergic reactions to iodinated radiocontrast media are rar e, and only a few well-documented cases of delayed-type hypersensitivity re actions caused by contrast media have been described. Methods We report a 61-year-old patient in whom percutaneous transluminal c oronary angioplasty (PTCA) was performed with iopamidol, a nonionic contras t medium. Seven days later, the patient developed generalized maculopapular exanthema. Repeated patch tests with several iodinated agents were perform ed. Results A first patch test with iopamidol was positive. Repetition of the p atch tests showed positive results to iopamidol as well as to iohexol and i oversol, two other nonionic contrast media, but not to other iodinated subs tances. Three months later, PTCA was repeated, and iopamidol was used again . Despite premedication, pruritic macular exanthema developed 1 day later. Whether iopamidol or trometamol - an additive substance in the contrast med ium - was causative could not be determined, since a third set of patch tes ts was negative. Conclusions Delayed-type hypersensitivity reactions to iodinated contrast m edia are rare. We recommend that patients with delayed exanthematous reacti ons undergo patch or intradermal tests with different contrast media and th eir additives, and that readings be performed immediately and later at days 2 and 3.