Allergic reactions at repeat femoral angiography with ioxaglate

Acute thyrotoxicosis secondary to destructive thyroiditis associated with cardiac catheterization contrast dye

BACKGROUND

Thyrotoxicosis caused by destructive thyroiditis is self-limited and results from the subacute release of preformed thyroid hormone. Common etiologies include painful subacute thyroiditis and silent (painless) subacute thyroiditis (including postpartum thyroiditis, amiodarone-associated destructive thyroiditis, and lithium-associated thyroiditis). Thyrotoxicosis commonly evolves slowly over a matter of weeks.

PATIENT FINDINGS

We report a unique case of severe thyrotoxicosis caused by acute- onset painful destructive thyroiditis in a patient who received large amounts of nonionic contrast dye Hexabrix® for cardiac catheterization. The results of thyroid function and physical examination were normal before the catheterization.

SUMMARY

The acute onset of severe thyroid pain, rapid increase in serum Free Thyroxine Index, and thyroglobulin concentrations with a triiodothyronine to free thyroxine index ratio of < 20 to 1 were compatible with an acute onset destructive thyroiditis, likely related to direct toxicity from the iodinated contrast material.

CONCLUSIONS

In light of the large number of patients who receive these contrast agents during cardiac catheterization, clinicians should be advised of this potentially serious complication, particularly in the setting of unstable cardiac disease.

[Immediate allergy to iodinated contrast agents and prevention of reactions]

The incidence and morbimortality of immediate hypersensitivity reactions following iodinated contrast media (ICM) injection remain unknown. The diagnosis of an immediate hypersensitivity reaction relies on a triad associating the precise description of the initial clinical manifestations and their delay of onset, the results of the biological assessment performed after the reaction including histamine and tryptase serum level measurements, and the results of skin testing with the culprit agent. Analysis of these data allows identification of the pathophysiologic mechanism of the reaction and the allergen involved in case of allergic hypersensitivity. Skin tests should be performed according to strict criteria. Cross-reactivity with ICM has to be investigated in order to propose a nonreactive ICM for future procedures. Allergic hypersensitivity to a given ICM imposes its definitive avoidance but not the avoidance of all iodinated drugs. The allergenic sequence has not yet been identified but is not the iodine atom itself. Asthma and treatment with beta-blockers are not risk factors of immediate allergic reactions to ICM per se, but may increase their severity. The various published protocols of premedication do not prevent the occurrence of an allergic/anaphylactic reaction to an ICM. The avoidance of the culprit ICM is the only way to prevent further reactions.

Allergy-like reactions to iodinated contrast agents. A critical analysis

Allergy-like reactions may occur following administration of iodinated contrast media (CM), mostly in at-risk patients (patients with history of previous reaction, history of allergy, co-treated with interleukin-2 or beta-blockers, etc.) but remain generally unpredictable. Severe and fatal reactions are very rare events. All categories of CM may induce such reactions, although first generation (high osmolar CM) have been found to induce a higher rate of adverse events than low osmolar CM. However, no differences were found between the two categories of CM with respect to mortality. Delayed reactions can also occur. There are no differences between the various categories of CM except for non-ionic dimers, which are more likely to induce such effect. Numerous clinical studies have evaluated the prophylactic value of drugs (mostly antihistamines and corticosteroids). Results are unclear and highly variable. Any prevention depends upon the mechanism involved. However, the mechanism of CM-induced allergy-like reaction remains disputed. Relatively recent data revived the hypothesis of a type-I hypersensitivity mechanism. Positive skin tests to CM have been reported. However, the affinity of IgE towards CM has been found to be very low in the only study which actually evaluated it. Other pathophysiological mechanisms (involving direct secretory effects on mast cells or basophils, or activation of the complement system associated or not with the plasma contact system) are also much debated. Anaphylaxis and anaphylactoid reactions are, in the end, clinically undistinguishable.