Endocrine Abstracts

Objective: To describe the mortality and vascular morbidity in patients after treatment for hyperthyroidism and hypothyroidism.

Method: We constructed an electronic database using record linkage of a community thyroid follow-up register, radioiodine database, regional biochemistry, regional prescribing database, hospital admissions and regional death certification. This was made possible by a unique patient identifier used locally for all healthcare episodes. We used a cohort study design with an eight year follow-up from 1994–2001, comparing patients with treated thyroid disease – with or without the need for long-term thyroxine – to the general population. The primary outcome was all-cause mortality. The secondary outcome was “serious vascular event” – the composite endpoint of non-fatal MI, non-fatal stroke or vascular death. Permission was obtained from the local ethics committee.

Results: There were 3,116,719 years follow up for the general population and 99,656 years for the thyroid population. The standard mortality ratio (SMR) for treated thyroid conditions adjusted for age and sex was 1.04 (95% CI 1.00–1.08), but when also adjusted for diabetes the SMR was 1.03 (95% CI 0.99–1.06).The Standard Incidence Ratio (SIR) for serious vascular events adjusted for age, sex and diabetes was 1.09 (95% CI 1.05–1.14). Event rates for non-fatal cardiovascular (SIR: 1.45; 1.34–1.56) and cerebrovascular disease (SIR: 1.26; 1.08–1.47) were increased in patients with treated hypothyroidism. Only cardiovascular disease events were increased in those with previous hyperthyroidism (SIR: 1.31; 1.17–1.46), not cerebrovascular disease (SIR: 1.14; 0.91–1.41). These findings were not predominantly in the first year of follow-up.

Conclusion: We found no increase in all-cause mortality in subjects with treated thyroid dysfunction. However there was an increased risk of serious vascular events which resulted from increased cardiovascular and cerebrovascular disease in patients with treated primary hypothyroidism. The reasons for increased serious vascular events in patients with apparently stabilised thyroid disease need further research.