What is the likely diagnosis for a middle-aged woman with worsening fatigue, dry skin, unintentional weight gain, and feeling cold, who has a history of hypertension, atrial fibrillation, and atherosclerotic cardiovascular disease, and is currently taking amlodipine (calcium channel blocker), amiodarone (antiarrhythmic), metoprolol (beta blocker), with delayed reflexes, hypotension, and bradycardia?

Amiodarone-Induced Hypothyroidism

This patient has amiodarone-induced hypothyroidism, a well-recognized complication of this antiarrhythmic medication that explains her constellation of symptoms (fatigue, dry skin, weight gain, cold intolerance), physical findings (bradycardia, delayed reflexes, diffuse dry skin), and hypotension.

Clinical Presentation Matches Classic Hypothyroidism

The patient presents with the textbook manifestations of hypothyroidism:

• Classic symptoms: Fatigue, dry skin, unintentional weight gain, and cold intolerance are the cardinal symptoms of hypothyroidism 1
• Physical examination findings: Diffuse dry skin, delayed reflexes, and bradycardia (heart rate 52) are characteristic physical signs 1, 2, 3
• Hemodynamic changes: Hypotension (100/60) and bradycardia result from decreased cardiac output and increased systemic vascular resistance that occur in hypothyroidism 4

Amiodarone as the Culprit Medication

Amiodarone is the most likely cause of her hypothyroidism given the temporal relationship and known mechanism:

• The patient started amiodarone 3 months ago for atrial fibrillation, and her symptoms developed over the past 6 months (overlapping timeline) 1
• Amiodarone is a well-recognized cause of both hypothyroidism and hyperthyroidism due to its high iodine content and direct thyroid effects 4
• The American College of Cardiology specifically recommends screening for hypothyroidism in patients treated with amiodarone 4

Compounding Effect of Beta-Blocker

The combination of hypothyroidism and metoprolol 50 mg twice daily is contributing to her marked bradycardia:

• Both hypothyroidism and beta-blockers independently cause bradycardia 1, 4
• The synergistic effect explains her heart rate of 52 bpm and hypotension 1
• Donepezil (if this is the unnamed medication) can also contribute to bradycardia, creating a triple mechanism for her slow heart rate 1

Diagnostic Confirmation Required

The next step is to measure TSH and free T4 to confirm the diagnosis:

• High TSH with low or normal free T4 confirms primary hypothyroidism 1
• This is the screening test recommended by the American Heart Association for patients with hypertension and cardiac disease 1
• Thyroid function testing is explicitly recommended in all patients presenting with heart failure or bradycardia 1, 4

Critical Management Considerations

Treatment must be initiated cautiously in this patient with significant cardiovascular disease:

• Start levothyroxine at a low dose (12.5-25 mcg daily) in patients with known coronary artery disease to avoid precipitating angina or arrhythmias 4, 3
• The American Medical Association recommends starting at 25-50 mcg/day in elderly patients or those with cardiac disease, titrating slowly 4
• Target TSH in the upper half of the reference range (2.5-5.0 mIU/L) initially rather than aggressive normalization 4

Medication adjustments are necessary:

• Consider reducing metoprolol dose once thyroid replacement begins, as bradycardia will improve with thyroid hormone normalization 1, 4
• Continue amiodarone if it is controlling her atrial fibrillation, but monitor thyroid function every 6-8 weeks during levothyroxine titration 4
• The patient urgently needs cardiology follow-up for her coronary artery disease with multiple blockages 1

Addressing the Cardiovascular Disease

Hypothyroidism is a recognized precipitant of acute decompensated heart failure and worsens coronary artery disease:

• The American College of Cardiology explicitly lists hypothyroidism as a common precipitant of heart failure decompensation 4
• Restoration of normal thyroid function may reverse abnormal cardiovascular function and improve her cardiac status 4
• Her hypotension (100/60) may improve with thyroid replacement as cardiac output increases 4

Common Pitfalls to Avoid

• Do not start levothyroxine at standard doses (1.5-1.8 mcg/kg/day) in patients with coronary artery disease, as this can precipitate myocardial infarction or unstable angina 4, 3
• Do not attribute all symptoms to age or other medications without checking thyroid function, especially in patients on amiodarone 1, 4
• Do not delay cardiology referral for her coronary artery disease while addressing the hypothyroidism—both require urgent attention 1
• Do not stop amiodarone abruptly without cardiology consultation, as this may precipitate recurrent atrial fibrillation 1

Monitoring Strategy

Once levothyroxine is initiated:

• Check TSH and free T4 every 6-8 weeks during dose titration 4
• Monitor for angina, palpitations, or worsening dyspnea that might indicate excessive thyroid replacement 4, 3
• Reassess blood pressure and heart rate at each visit, adjusting metoprolol as needed 1
• Continue thyroid function monitoring every 2-3 months in patients with atrial fibrillation or serious cardiac disease 4