Thyroid Dysfunction and Hypertension: What's the Connection?

Q: Is hypertension a frequent manifestation of thyroid disease?Which clinical clues suggest hypertension in persons with thyroiddysfunction?A: The prevalence of hypertension among patients with hypothyroidism isapproximately 3%. Hypertension is much more frequently associated withthyrotoxicosis (hyperthyroidism); the prevalence is estimated at 20% to 30%.Thyrotoxicosis. In patients with this condition, systolic pressures are typicallyelevated and diastolic pressures are often low, which results in a widenedpulse pressure. These findings are attributable to increased cardiac output,stroke volume, heart rate, and cardiac contractility. Other manifestations of thyrotoxicosisare usually readily apparent; they include exophthalmos, nervousness,emotional lability, heat intolerance, and excessive perspiration. Palpitations,weight loss despite increased appetite, diarrhea, fatigue, and insomnia may alsobe observed. Anginal symptoms occur occasionally. The thyroid gland is usuallypalpably enlarged; however, it is normal size or smaller in about 40% of elderlypatients. A discrete nodule or multiple nodules may not be readily apparentLow levels of thyroid-secreting hormone (TSH) confirm the diagnosis.Appropriate therapy with restoration of normal thyroid function usually leadsto normalization of blood pressure, particularly in younger patients.Hypothyroidism. In patients with hypothyroidism, both systolic and diastolicpressures are elevated; the severity of the thyroid disorder seems to correlatewith the increase in diastolic pressure. The onset of hypothyroidism maybe subtle and unrecognized for a prolonged period; therefore, elevated diastolicblood pressure may represent a valuable clinical clue in older persons, in whomsystolic hypertension typically predominates.Other clinical manifestations include lethargy and decreased activity tolerance,dry skin, cold intolerance, constipation, intellectual impairment, andhoarseness. Typically, the thyroid gland is not enlarged, although a goiter maybe readily palpable. The diagnosis is easily confirmed with measurement ofserum TSH, which is elevated in 95% of cases.Endocrine and cardiovascular changes in thyroid disorders. The Tablelists changes observed in both hyperthyroidism and hypothyroidism.Although many symptoms of thyrotoxicosis can be controlled with ß-adrenergicblockers, catecholamine levels are usually normal or even decreased. Despitethe fact that the activity of the renin-angiotensin-aldosterone (RAA) systemis increased in patients with thyrotoxicosis, angiotensin-converting enzyme inhibitorsand angiotensin II receptor blockers do not always reduce blood pressure.Thus, the role of the RAA system in hypertension associated with thyrotoxicosisremains to be defined. In addition, because of the hyperdynamic circulation,peripheral vascular resistance tends to decline in thyrotoxicosis. This mayhelp explain some of the hemodynamic changes.In contrast, patients with hypothyroidism have increased catecholaminelevels and a decreased density of ß-adrenergic tissue receptor activity. One hypothesisis that the reduction in ß-adrenergic activity leads to increased œ-adrenergicresponses, which may explain the increased peripheral vascular resistanceand hypertension. The reduced activity of the RAA system in hypothyroidismsuggests that this system plays only a small role in concomitant hypertension.Treatment. Initial management of hypertension resulting from hyperthyroidismincludes a ß-adrenergic blocker to control blood pressure and othersymptoms. Subsequent therapy is cause-specific. The usual treatment of patientswith autoimmune hyperthyroidism (Grave disease) is ablation of the thyroidgland with radioactive sodium iodide (¹³¹I). In those with a multinodulargoiter (Plumber disease), ablation therapy is usually followed by subtotal thyroidectomy.Always consider subacute thyroiditis in the initial differential; thisdisorder can be effectively treated with short-term ß-blocker therapy.The treatment of choice in hypothyroidism is levothyroxine replacementtherapy, with gradual titration to a target dose. A smaller initial dose and moregradual titration are recommended for older patients, particularly those withcardiac disease.