Endocrine Abstracts

Hyperthyroidism is known to result in excess all-cause and circulatory mortality. We set out to identify which factors predict mortality in 1290 patients (1019 females and 271 males) with overt hyperthyroidism and determined if treatment with antithyroid drugs or radioactive iodine (¹³¹I) affect outcome. All individuals were aged ≥40 years (median: 57.5 years) and presented to our clinic between 1989 and 2003. Cause of death was compared with age- and period specific mortality in England and Wales. In 13 443 person-years of follow-up (median duration of follow-up 10 years), 345 subjects died versus 287 expected deaths (all cause SMR: 1.20 (95% CI: 1.08–1.34), P=0.001) and mortality from circulatory (SMR 1.25 (1.06–1.48), P=0.009) and respiratory diseases (SMR 1.33 (1.02–1.48), P=0.03) were significantly increased. On multivariate analyses, all cause mortality was higher in males (HR 1.37 (1.05–1.79), P=0.02), in smokers (HR 1.66 (1.31–2.10), P<0.001), and in those presenting with atrial fibrillation (HR 1.88 (1.44–2.45), P<0.001). The underlying cause of hyperthyroidism, classified as Graves’ disease (n=365), toxic nodular hyperthyroidism (n=286) or indeterminate aetiology (n=639), did not significantly affect outcome. 466 subjects were treated with antithyroid drugs only and 824 received ¹³¹I therapy resulting in hypothyroidism in 532. Mortality rates were similar when comparing those treated with drugs only with subjects rendered euthyroid following ¹³¹I (HR 0.95 (0.72–1.24), P=NS). Induction of hypothyroidism following radioiodine was associated with significantly reduced all-cause (HR 0.69 (0.52–0.91), P=0.01) and circulatory mortality (HR 0.65 (0.42–1.00), P=0.05), even after correcting for other vascular risk factors.

Conclusions: We have confirmed significantly increased all-cause and circulatory mortality in patients with hyperthyroidism. Furthermore, these data indicate that the administration of doses of radioactive iodine sufficient to induce hypothyroidism is associated with significantly improved survival versus therapy with lower doses of ¹³¹I as well as treatment with antithyroid drugs only.