Iodine-induced thyroid dysfunction: comment on "association between iodinated contrast media exposure and incident hyperthyroidism and hypothyroidism".

BACKGROUND Sudden exposure to high iodide levels may cause thyroid dysfunction. Despite compelling biological plausibility and clinical implication, the association between iodinated contrast media exposure and incident hyperthyroidism and hypothyroidism has not been rigorously studied. METHODS We performed a nested case-control study of patients treated between January 1, 1990, and June 30, 2010, who did not have preexisting hyperthyroidism or hypothyroidism. In parallel analyses, incident hyperthyroid or hypothyroid cases were defined by a change in thyrotropin level from normal (at baseline) to low or high (follow-up measurement). Euthyroid controls were selected using an incidence density sampling approach and were matched to cases on the basis of age, sex, race/ethnicity, estimated glomerular filtration rate, follow-up thyrotropin measurement date, and interval between baseline and the follow-up thyrotropin measurement date. Iodinated contrast media exposure was assessed using claims data for contrast-enhanced computed tomography or cardiac catheterization. RESULTS In total, 178 and 213 incident hyperthyroid and hypothyroid cases, respectively, were matched to 655 and 779 euthyroid controls, respectively. Iodinated contrast media exposure was associated with incident hyperthyroidism (odds ratio [OR], 1.98; 95% CI, 1.08-3.60), but a statistically significant association with incident hypothyroidism was not observed (OR, 1.58; 95% CI, 0.95-2.62). In prespecified secondary analysis, iodinated contrast media exposure was associated with incident overt hyperthyroidism (follow-up thyrotropin level ≤ 0.1 mIU/L; OR, 2.50; 95% CI, 1.06-5.93) and with incident overt hypothyroidism (follow-up thyrotropin level >10 mIU/L; OR, 3.05; 95% CI, 1.07-8.72). CONCLUSION Iodinated contrast media exposure is associated with subsequent development of incident hyperthyroidism and incident overt hypothyroidism.