Association of Hypertension and Hyperthyroidism in a Subspecialty Clinic and a National Database

Ana M. Rivas, MD; Jeff Dennis, PhD; Camilo Pena, MD; Jonathan Kopel, BS; Kenneth Nugent, MD

Disclosures

South Med J. 2020;113(12):607-611. 

In This Article

Discussion

The prevalence of hypertension is higher in hyperthyroid patients than in the general population, and in our clinical cohort, it is higher (50%) than the prevalence reported in other studies on hyperthyroid patients (20%–30%).[7,8] This is possibly explained by the number of older patients in our study.[5,7] Systolic blood pressures and not diastolic blood pressures are more frequently elevated in hyperthyroid patients,[8] possibly because of the increased cardiac output and decreased peripheral vascular resistance in hyperthyroid patients, resulting in wide pulse pressures in these patients. The recognition of hypertension in patients with hyperthyroidism is clinically relevant because other studies have reported that blood pressure often normalizes shortly after starting treatment with antithyroidal therapy.[8]

In our clinical cohort, patients with hypertension did not have higher thyroid hormone levels. The degree of thyroid hormone elevation does not necessarily correlate with the severity of the symptoms in thyrotoxicosis or with the development of complications.[11] This is probably explained by the fact that circulating hormone levels do not necessarily reflect tissue hormone levels. In addition, there are genetic factors that modulate an individual's sensitivity to thyroid hormone, and patients who happen to be more sensitive to these hormones present with more severe symptoms or complications of thyrotoxicosis, such as hypertension. Analysis of the NHANES data found a significant positive association between systolic blood pressure and FT3 levels both as a continuous variable and a categorical variable. Small increments of systolic blood pressure may have important clinical effects even when the values are in the normal range.[18] In addition, hemoglobin levels were similar in our two patient groups. This variable was examined because increased hemoglobin levels may increase preload in these patients.[7] In addition, Ca2+ was similar in the two groups. Finally, unlike other studies, we did not find a correlation between body mass index and blood pressure.[8]

Older age was the only parameter found to be significantly different in the two groups of our clinic patients. Advanced age is a risk factor for hypertension, but a prevalence of 85% in patients older than 45 years is much higher than the prevalence reported in the general population.[2] It is possible that older patients with hyperthyroidism have a higher risk for the development of hypertension than younger patients with hyperthyroidism and that this risk is higher than expected at any particular age. Older clinic patients (55 years and older) had significantly lower FT3 and FT4 levels than younger clinic patients with hypertension, suggesting increased sensitivity to the cardiovascular effects of thyroid hormones. Apathetic hyperthyroidism occurs more frequently in older patients who tend to present with fewer classic symptoms of hyperthyroidism and instead present with symptoms that can be easily confused with normal aging, such as weakness, weight loss, lethargy, and depression.[10] This subtle presentation can delay the recognition of hyperthyroidism in these patients, and, if the patient is hypertensive, he or she may be incorrectly diagnosed as having primary hypertension. Published data on the association between age and hypertension in patients with hyperthyroidism are limited. A study with 321 hyperthyroid patients ages 20 to 59 did not find an age-related increase in systolic blood pressure,[19] but another study with 51 patients younger than 50 did find a correlation between systolic blood pressure and age in hyperthyroid individuals.[8] Hurxthal[20] reported information systematically collected on 458 patients with toxic goiter who underwent surgical procedures. Systolic blood pressures increased with age in these patients and decreased following surgical treatment. There was no consistent relation between blood pressure and basal metabolic rate.

Our study has definite limitations, and these include its retrospective nature, the use of one blood pressure measurement to make the diagnosis, and the small sample size of our clinic cohort. In addition, considering that the categorization of hypertension was based on a blood pressure measurement obtained in the office, it is possible that the frequency of hypertension is overestimated due to "white coat hypertension," which is thought to occur in 26% to 46% of patients.[21] We therefore analyzed a nationally representative sample from NHANES to better assess the relation between hyperthyroidism and hypertension. The two samples are not intended to mirror each other, given the differences in selection to an endocrinology clinic population versus a national sample of adults; however, we believe that the comparison adds breadth to our exploration of this association.

NHANES provides a much larger sample and indicates a meaningful association between FT3 levels and systolic blood pressures. We believe that this information highlights the importance of screening for hyperthyroidism in patients with hypertension, even when diagnosed at a more advanced age, when primary hypertension is more common. Older patients can sometimes present with extremely mild symptoms of hyperthyroidism, resulting in a delay in the diagnosis. The US Preventive Services Task Force has recommended against screening for thyroid dysfunction in nonpregnant asymptomatic adults.[22] The American College of Cardiology/American Heart Association guidelines advise consideration of laboratory testing (which includes a TSH) for secondary hypertension in the context of increased hypertension severity, poor response to standard treatment approaches, or a disproportionate severity of target organ damage for the level of hypertension.[3] Whether these characteristics occur with hypertension as a result of hyperthyroidism is unknown and would require a large longitudinal study to characterize these outcomes. We believe, however, that it is important for clinicians to know about the high frequency of hypertension in patients with hyperthyroidism, especially in older adults. Future prospective studies to determine the frequency of thyroid dysfunction patients with a new diagnosis of hypertension would be useful.

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