Macular exanthema appearing 5 days after X-ray contrast medium administration

We report a case of widespread, pruritic macular exanthema appearing 5 days after intravenous administration of the X-ray contrast medium, iohexol (Omnipaque) in a patient who had not previously received any X-ray contrast medium. The eruptions resolved in 7 days, leaving no residual lesions. When the patient was challenged intradermally with the same contrast medium 1.5 months after recovery, the same type of eruption developed 1 day after challenge. Histological examination of biopsies from positive skin test sites revealed the presence of a dermal infiltrate of lymphocytes. This case is another example of a late-onset adverse reaction to an X-ray contrast medium, mediated by specific T cells. The usefulness of intradermal skin testing for confirming the allergic nature of the reaction and for studying cross-reactivity pattern is emphasized.