What is the best treatment approach for a patient with hypothyroidism (underactive thyroid) and hypertension (high blood pressure)?

Treatment of Hypothyroidism and Hypertension

Treat the hypothyroidism first with levothyroxine replacement therapy, as this alone normalizes blood pressure in approximately 50% of patients with both conditions, and then add antihypertensive medications only if hypertension persists after achieving euthyroidism. 1, 2

Initial Diagnostic Approach

Screen for hypothyroidism in all newly diagnosed hypertensive patients by measuring thyroid-stimulating hormone (TSH), as hypothyroidism is a remediable cause of hypertension that is often overlooked. 1

Key Pathophysiologic Connection

Hypothyroidism causes hypertension through several mechanisms: 3, 1

• Increased systemic vascular resistance (up to 50% elevation) 3, 1
• Diastolic hypertension is particularly common due to increased peripheral resistance 1
• Increased aortic stiffness, which predicts whether hypertension will be reversible with thyroid replacement 2
• Bradycardia and decreased cardiac output, though clinical heart failure is rare 3, 1

Treatment Algorithm

Step 1: Initiate Levothyroxine Replacement

Start levothyroxine at reduced doses in patients with coexisting hypertension and cardiac disease to avoid precipitating angina or arrhythmias: 1, 4

• Young, healthy patients: 1.6 mcg/kg daily 4
• Elderly or those with cardiovascular disease: Start at 25-50 mcg daily 4
• Target TSH initially: 2.5-5.0 mIU/L rather than aggressive normalization 1

Step 2: Monitor Blood Pressure Response

Reassess blood pressure after 6-8 weeks of achieving euthyroidism before adding antihypertensive medications: 2, 5

• 50% of patients will have complete normalization of blood pressure with levothyroxine alone 2
• 32-40% of hypothyroid hypertensive patients achieve diastolic BP <90 mmHg with thyroid replacement only 6
• Blood pressure reduction correlates with decreased aortic stiffness 2

Step 3: Add Antihypertensive Therapy if Needed

If hypertension persists after achieving euthyroidism, initiate combination antihypertensive therapy targeting BP <130/80 mmHg: 3

Preferred first-line combination: 3

• RAS blocker (ACE inhibitor or ARB) + dihydropyridine calcium channel blocker (CCB), OR
• RAS blocker + thiazide/thiazide-like diuretic

Use fixed-dose single-pill combinations to improve adherence 3

Specific consideration for persistent hypertension: Calcium channel blockers (particularly felodipine) are highly effective in patients whose hypertension doesn't fully resolve with levothyroxine, as they reduce both blood pressure and aortic stiffness. 2

Step 4: Escalate if BP Target Not Achieved

If BP remains uncontrolled on two-drug combination, advance to three-drug therapy: RAS blocker + dihydropyridine CCB + thiazide/thiazide-like diuretic, preferably as a single-pill combination. 3

Critical Safety Considerations

Levothyroxine Initiation in Cardiac Disease

Start low and go slow in patients with hypertension and cardiac comorbidities: 1, 4

• Overtreatment can cause angina, arrhythmias, and increased cardiac wall thickness 1
• Monitor weekly until symptoms stabilize 4
• Recheck TSH and free T4 every 6-8 weeks after dose adjustments 4

Beta-Blocker Use

Avoid beta-blockers as first-line antihypertensives unless compelling indications exist (post-MI, heart failure with reduced ejection fraction, angina), as they are less effective for primary hypertension. 3

However, beta-blockers are specifically indicated if the patient has symptomatic hyperthyroidism or thyrotoxicosis during the diagnostic workup, as propranolol treats tachycardia and tremor. 3

Monitoring Strategy

Ongoing surveillance after treatment initiation: 3, 4

• TSH and free T4 every 6-8 weeks until stable 4
• Blood pressure at each visit 3
• Once stable, annual thyroid function tests 4
• Adjust levothyroxine in 12.5-25 mcg increments if TSH remains elevated 4

Common Pitfalls to Avoid

Do not add antihypertensive medications before achieving euthyroidism, as this may result in overtreatment and hypotension once thyroid function normalizes. 5, 7

Do not assume hypertension is essential (primary) without checking TSH, as hypothyroidism accounts for 1.2-3.6% of hypertensive patients and is readily treatable. 6

Do not use aggressive TSH targets (<2.5 mIU/L) in elderly or cardiac patients, as maintaining TSH in the upper half of the reference range (2.5-5.0 mIU/L) is safer and acceptable. 1

Patients with increased aortic stiffness are less likely to have complete BP normalization with levothyroxine alone and will likely require antihypertensive medications. 2