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

Abstract and Introduction

Abstract

Objective: Hypertension can cause significant morbidity and reduced life expectancy. Most patients with hypertension have primary hypertension; however, 10% to 15% have secondary hypertension. Endocrine disorders as a secondary cause occur in approximately 10% of patients with secondary hypertension, and thyroid disorders account for approximately 1% of all patients with hypertension. The identification of patients with hyperthyroidism has important benefits for these particular patients. The objective of this study was to examine the occurrence of high blood pressure in patients with hyperthyroidism.

Methods: We reviewed the clinical information available from 414 new patients referred to an endocrinology clinic in west Texas for evaluation of hyperthyroidism. The final cohort included 96 patients who had both thyroid laboratory tests and blood pressure measurements at the time of their clinic visit. We also examined this relationship in a nationally representative sample of US adults (National Health and Nutrition Examination Survey 2007–2012), which included thyroid test results and at least one blood pressure measurement (N = 8837).

Results: Sixty-five of these clinic patients had elevated blood pressure based on criteria suggested by the American College of Cardiology/American Heart Association. These patients had similar thyroid hormone levels as patients who did not have hypertension but tended to be older. Ordinary least squares regression analysis of the National Health and Nutrition Examination Survey 2007–2012 data demonstrated a significant positive association between free T3 levels and systolic blood pressure, adjusting for age, sex, and the use of levothyroxine.

Conclusions: These findings from a specialty clinic and a national sample suggest that clinicians should consider the possibility of hyperthyroidism in patients with hypertension, even in older patients.

Introduction

Hypertension affects 26.4% of the adults in the world[1] and >30% of adults older than 20 years in the United States.[2] Its frequency increases with age, and estimates suggest that it is present in 10% of patients 20 to 44 years old and in 78% in patients 75 years or older.[3] Blood pressure cutoffs used for the definition of hypertension vary among different medical societies. The Joint National Committee 7 defines hypertension as a systolic blood >140 mm Hg or a diastolic blood pressure >90 mm Hg,[4] whereas the American College of Cardiology/American Heart Association guidelines recommend lower cutoffs of >130 and >80 mm Hg for systolic and diastolic blood pressure, respectively.[2]

Primary hypertension is the most common cause of hypertension and accounts for approximately 85% of cases. An underlying cause of hypertension can be identified in 10% to 15% of adults with hypertension, and these cases are classified as secondary hypertension.[3] Recognizing the features of secondary hypertension provides an opportunity for targeted management and even curative therapy for hypertension in some patients.[5] Furthermore, analysis of patients with secondary hypertension can increase our understanding of the pathophysiology and prognosis of hypertension. Abnormal blood pressure can occur in at least 10 different endocrine disorders, and these represent an important group of secondary causes of hypertension.[6] Although hyperthyroidism is identified as a secondary cause of hypertension in <1% of cases, the frequency of hypertension in patients with hyperthyroidism is high and has been estimated at 20% to 30%.[7,8] Iglesias and colleagues studied 20 normotensive patients with hyperthyroidism using 24-hour blood pressure monitoring before and after the treatment of hyperthyroidism and reported an average 5-mm Hg decrease in systolic blood pressure despite a 5.7-kg weight gain after treatment.[9]

Most patients with hyperthyroidism present with high thyroid hormones (thyroxine and/or triiodothyronine) in the setting of a low thyroid-stimulating hormone (TSH). TSH measurement is a readily available test and allows the identification of hyperthyroidism, especially in those patients presenting with mild symptoms related to hyperthyroidism, as is common in older patients.[10] We conducted a retrospective study of blood pressure in patients referred to an endocrinology outpatient clinic for the evaluation of hyperthyroidism to determine the prevalence of hypertension in adult patients. We classified patients by age and compared the frequency of hypertension in each age group. Given the nonrandom selection of patients who see an endocrinologist, we further explored the association between hyperthyroidism and hypertension in a nationally representative adult sample from the 2007–2012 National Health and Nutrition Examination Survey (NHANES).

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