Radioiodine therapy increases the risk of cerebrovascular events in hyperthyroid and euthyroid patients.
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.
Department of Clinical PhysiologyNuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Nodre Ringvej 57, 2600 Glostrup, DenmarkDepartment of Clinical Physiology and Nuclear MedicineUniversity Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, DenmarkPrimary Health CareRegion Zealand, Ågade 10, 4700 Næstved, DenmarkSection of EndocrinologyDepartment of Medicine, University Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, Denmark jeppe.lerche.la.cour.01@regionh.dk jeppelerche@hotmail.com.
Jeppe Lerche
JL
la Cour
Department of Clinical PhysiologyNuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Nodre Ringvej 57, 2600 Glostrup, DenmarkDepartment of Clinical Physiology and Nuclear MedicineUniversity Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, DenmarkPrimary Health CareRegion Zealand, Ågade 10, 4700 Næstved, DenmarkSection of EndocrinologyDepartment of Medicine, University Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, Denmark.
Lars Thorbjoern
LT
Jensen
Department of Clinical PhysiologyNuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Nodre Ringvej 57, 2600 Glostrup, DenmarkDepartment of Clinical Physiology and Nuclear MedicineUniversity Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, DenmarkPrimary Health CareRegion Zealand, Ågade 10, 4700 Næstved, DenmarkSection of EndocrinologyDepartment of Medicine, University Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, Denmark.
Anders
A
Vej-Hansen
Department of Clinical PhysiologyNuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Nodre Ringvej 57, 2600 Glostrup, DenmarkDepartment of Clinical Physiology and Nuclear MedicineUniversity Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, DenmarkPrimary Health CareRegion Zealand, Ågade 10, 4700 Næstved, DenmarkSection of EndocrinologyDepartment of Medicine, University Hospital of Herlev, Herlev Ringvej 75, 2730 Herlev, Denmark.
Birte
B
Nygaard
D000328:Adult; D000368:Aged; D002561:Cerebrovascular Disorders / Q000453:epidemiology / Q000209:etiology*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006044:Goiter, Nodular / Q000453:epidemiology / Q000532:radiotherapy*; D006801:Humans; D006980:Hyperthyroidism / Q000453:epidemiology / Q000532:radiotherapy*; D007457:Iodine Radioisotopes / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D012042:Registries / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D012306:Risk
D007457:Iodine Radioisotopes