D2.305 - Acute generalized exanthematous pustulosis due to iohexol with tolerance to iobitridol

Iodinated contrast media (ICMs) are commonly used in routine radiological diagnostic procedures. The estimated prevalence of adverse reactions to ICMs ranges from 0.5% to 2%, with delayed responses being the most frequently reported. While maculopapular exanthema is the most common clinical manifestation, severe cutaneous adverse reactions (SCARs) have also been documented.

Diagnosing SCARs caused by ICMs can be challenging, as positive reactions to skin tests occur in only 47% of patients. A challenge test using the suspected ICM may be necessary in certain cases.

We present a case that seems to be acute generalized exanthematous pustulosis (AGEP) induced by hypersensitivity to iohexol. A controlled provocation test confirmed the diagnosis despite negative skin test results.

A 53-year-old female with ANCA-associated systemic vasculitis developed a non-pruritic macular erythematous eruption on her trunk and limbs two days after starting oral cyclophosphamide for acute renal failure. The rash worsened, prompting the discontinuation of cyclophosphamide. The episode resolved spontaneously within one week without residual lesions or desquamation.

Four days prior to the onset of the rash, the patient had undergone an imaging study using an unspecified ICM.

The allergy evaluation was conducted six months after the initial reaction.

Skin prick and intradermal tests (ST) were negative, including immediate and delayed readings for cyclophosphamide and ICMs (iohexol, ibiotridol, and iodixanol).

Given that both pharmacological agents were essential for the patient, controlled exposure tests were performed over two days.

STs and oral challenges with cyclophosphamide yielded negative results.

One month later, STs with the aforementioned ICMs remained negative. However, the intravenous challenge with iohexol was positive; 48 hours later, the patient developed a reaction consistent with AGEP, which was resolved with methylprednisolone.

Since providing an alternative ICM was crucial, a challenge test with iobitridol was conducted one month later, demonstrating tolerance.

This report presents a case consistent with AGEP induced by iohexol, with confirmed tolerance to iobitridol.

Cross-reactivity among ICMs in AGEP has been sparsely studied, primarily using skin tests.

Our findings demonstrate sensitization to iohexol with tolerance to iobitridol through challenge testing in a case consistent with AGEP.