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Untreated hyperthyroidism increases CVD risk
Among adults with hyperthyroidism, treatment for the condition can mitigate their increased risk for cardiovascular disease, according to findings published in Thyroid. In addition, longer periods of decreased thyroid-stimulating hormone elevate CVD mortality for treated and untreated adults with hyperthyroidism.
“A substantial proportion of patients with hyperthyroidism, independent of the diligence of their caring physicians, will have periods with subnormal TSH and therefore run an higher risk than the background population of dying from cardiovascular disease,” Laszlo Hegedüs, MD, DMSc, professor of medicine and endocrinology at the University of Southern Denmark and a senior consultant physician in the department of endocrinology and metabolism at Odense University Hospital in Odense, Denmark, told Endocrine Today.
To determine whether treatment for hyperthyroidism influences CVD risk, Lillevang-Johansen and colleagues performed a case-control study within a population-based cohort of adults with at least one TSH measure between 1995 and 2011. All patients were registered in the Odense Patient data Explorative Network (OPEN), which collected data on the island of Funen in Denmark.
Patients were categorized as euthyroid (n = 214,672; mean age, 49.6 years; 57.5% women), hyperthyroid treated (n = 1,432; mean age, 58.1 years; 82.3% women) or hyperthyroid untreated (n = 1,063; mean age, 61.7 years; 75.3% women). Patients were deemed euthyroid if they consistently had TSH levels between 0.3 mIU/L and 4 mIU/L; hyperthyroidism was defined as a baseline TSH level less than 0.3 mIU/L and at least two TSH values lower than the first measurement in a 6-month period. Patients were considered treated for hyperthyroidism if they were prescribed at least one antithyroid medication or underwent thyroid surgery or radioactive iodine treatment. Prescription data were collected from the Danish National Prescription Registry, and surgery and radioactive iodine treatment were confirmed in the Danish National Patient Registry.
Patients who experienced a CVD event, which included myocardial infarction, stroke, atrial fibrillation, heart failure or CVD death, were matched with up to three sex- and age-matched controls without CVD. CVD events were confirmed via the Danish National Patient Registry.
Using euthyroid patients as reference, the researchers found that patients with untreated hyperthyroidism were at higher risk for CVD (OR = 1.21; 95% CI, 1.03-1.42), even when adjusting for comorbidities (OR = 1.25; 95% CI, 1.06-1.48). Patients with treated hyperthyroidism were also at increased risk vs. the euthyroid group (OR = 1.04; 95% CI, 0.89-1.2), but not to the same degree as untreated patients, even when adjusting for comorbidities (OR = 1.04; 95% CI, 0.9-1.22).
For every 6 months of decreased TSH, the OR for CVD events was 1.09 (95% CI, 1.05-1.14) in the hyperthyroid-treated group and 1.1 (95% CI, 1.05-1.15) in the hyperthyroid-untreated group. The researchers noted that this equated to increased risk for CVD events per 5 years of 137% in hyperthyroid-treated patients and 159% in hyperthyroid-untreated patients.
“It is unlikely that a prospective randomized blinded study will ever be carried out, for obvious ethical reasons. Therefore, this is as close as we will ever come to provide evidence of the importance of not only treating hyperthyroidism, but to treat it well and avoid/limit periods of subnormal TSH,” Hegedüs said. “Our data suggest that also mild hyperthyroidism (subclinical hyperthyroidism) carries this excess morbidity and mortality. This risk seems to be independent of age, suggesting that there is no age limit under which treatment for hyperthyroidism should not be offered.” – by Phil Neuffer
Disclosures: Hegedüs reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.