Radioiodine therapy increases the risk of cerebrovascular events in hyperthyroid and euthyroid patients.

BACKGROUND AND OBJECTIVE: Hyperthyroid patients treated with radioiodine have increased morbidity and mortality from cerebrovascular events. This risk has until now has been attributed to the hyperthyroidism. However, radioiodine therapy of benign thyroid diseases exposes the carotid arteries to radiation and is capable of inducing atherosclerosis. The objective of the study was to elucidate whether ionizing radiation from radioiodine might contribute to cerebrovascular morbidity. METHODS: In a retrospective register cohort study, 4000 hyperthyroid and 1022 euthyroid goitre patients treated with radioiodine between 1975 and 2008 were matched 1:4 on age and sex with random controls. The cohort was followed from the date of treatment until hospitalization due to cerebrovascular event, death, 20 years of follow-up or March 2013. Data were analyzed in competing risk models adjusting for age, sex, Charlson's comorbidity score, atrial fibrillation and previous cerebrovascular events. RESULTS: Mean follow-up time was 11.5 years, mean age 61 years, with a total number of 3228 events. Comparing all radioiodine-treated patients with controls, the fully adjusted model showed increased risk of cerebrovascular events among all treated patients, hazard ratio (HR) 1.18 (95% CI 1.09-1.29). The risk was increased among hyperthyroid (HR 1.17; 95% CI 1.07-1.28) as well as euthyroid patients (HR 1.21; 95% CI 1.02-1.44). CONCLUSIONS: We report an increased risk of cerebrovascular events in hyperthyroid as well as euthyroid patients treated with radioiodine for benign thyroid disorders. That these patient groups have similar risks suggests the possibility that radiation from radioiodine contributes to cerebrovascular morbidity via acceleration or initiation of atherosclerosis.

[Iodine uptake and the effect of radioiodine treatment--status after the addition of iodine to salt]. / Jodoptagelse og effekt af radiojodbehandling--status efter jodtilsaetning til husholdningssaltet.

INTRODUCTION: Iodine uptake and the effect of radioiodine treatment of nontoxic goiter were investigated after the introduction of iodine to salt. MATERIALS AND METHODS: A retrospective study was done of 61 patients (48 women and 13 men with a median age of 56 (range 28-78)) with nontoxic goiter, examined by 24-hour radioiodine uptake. 42 of the patients were treated with radioiodine (median 600 MBq, range 200-600 MBq). The results were compared with those from a study done 10 years ago in the same area. RESULTS: Iodine uptake decreased significantly, from 40% (range 16-67%) in 1981-1993 to 25% (range 13-62%) in 2001-2003. 38 of the 42 patients were examined, and of these 34 (90%) had benefited from the treatment (53% of the 38 patients showed a complete effect) as estimated by the patient and the physician, based on the patient's original symptoms and the physician's clinical judgement. Four patients developed hypothyroidism, one radiation-induced thyroiditis and three Graves" disease. DISCUSSION: Iodine uptake is significantly lowered after the addition of iodine to salt. Radioiodine therapy of nontoxic goiter will continue to be effective.