Endocrine Abstracts

Objective: Untreated overt hyperthyroidism is known to predispose the patient to cardiovascular diseases, while predisposition in subclinical hyperthyroidism has been debated. The1 cut-off point of TSH for initiating treatment in subclinical hyperthyroidism is still undefined.

Method: A community-based prospective study including non-hospitalised participants, aged 51 to 91 years, living in Copenhagen, Denmark were examined between September 1998 and January 2000 and provided blood and urinary samples on inclusion. All participants had normal left ventricular ejection fraction (LVEF >50%), estimated by echocardiography, and were without heart or renal failure. The follow-up period was up to 5 years (to December, 2003). The local ethical committee approved the study.

Results: 609 participants were included in the study, 549 (90.1%) were euthyroid (TSH 0.4–4.0 mU/L), 34 (5.6%) had TSH >4.0 mU/L and 26 (4.3%) had TSH <0.4 mU/L. Three were overt hypothyroid and one overt hyperthyroid. Of the participants having TSH ≤4.0 mU/L, 86 died and 59 had first major cardiovascular event during follow-up. In the subclinical hyperthyroid group, the mean value of TSH was 0.2 mU/L (range 0.0–0.4 mU/L). The incidence of major cardiovascular events incl. cardiovascular dead (r=0.8, P=0.04), as well as the incidence of stroke (r=1.4, P=0.01) was increased among the subclinical hyperthyroid participants. The TSH <0.4 mU/L were independently associated with the risk of stroke (r=1.2, P=0.03), hazard ratio 3.28, even after adjusting for sex, age and atrial fibrillation.

Conclusion: Subclinical hyperthyroidism was a risk factor for developing major cardiovascular events including cardiovascular dead, in particular stroke, in a group of 575 non-hospitalised individuals with TSH ≤4.0 mU/L, aged 51 to 91 years. On this perspective, we recommend the condition subclinical hyperthyroidism to be treated as a disease instead of a condition to be observed.