What is the recommended initial evaluation and treatment approach for a patient presenting with potential hypothyroidism or hyperthyroidism symptoms?

Initial Evaluation and Treatment of Thyroid Symptoms

Diagnostic Approach

For any patient presenting with potential thyroid dysfunction, measure TSH as the primary screening test, followed by free T4 if TSH is abnormal, to distinguish between subclinical and overt disease. 1, 2

Initial Laboratory Testing

• TSH is the most sensitive test for thyroid dysfunction, with sensitivity above 98% and specificity greater than 92% 1
• If TSH is elevated, measure free T4 to distinguish subclinical hypothyroidism (normal free T4) from overt hypothyroidism (low free T4) 1
• If TSH is suppressed, measure free T4 and free T3 to distinguish subclinical hyperthyroidism (normal hormones) from overt hyperthyroidism (elevated hormones) 3
• Confirm any abnormal TSH with repeat testing after 3-6 weeks, as 30-60% of elevated TSH levels normalize spontaneously 1

Additional Testing for Hypothyroidism

• Measure anti-TPO antibodies to identify autoimmune etiology (Hashimoto's thyroiditis), which predicts higher progression risk—4.3% per year versus 2.6% in antibody-negative individuals 1
• Check lipid profile, as subclinical hypothyroidism may affect cholesterol levels 1

Additional Testing for Hyperthyroidism

• Measure TSH-receptor antibodies to diagnose Graves' disease (the cause in 70% of hyperthyroidism cases) 4
• Obtain thyroid ultrasonography to evaluate for nodules or goiter 4
• Consider thyroid scintigraphy if nodules are present or etiology is unclear 3

Treatment Algorithm for Hypothyroidism

When to Initiate Levothyroxine Immediately

Start levothyroxine without delay in the following situations: 1, 5

• TSH >10 mIU/L regardless of symptoms or free T4 level (carries ~5% annual risk of progression to overt hypothyroidism) 1
• Any TSH elevation with low free T4 (overt hypothyroidism) 1, 2
• Pregnant women or those planning pregnancy with any TSH elevation 1, 5
• Symptomatic patients with TSH 4.5-10 mIU/L who have fatigue, weight gain, cold intolerance, or constipation 1

Levothyroxine Dosing Strategy

For patients <70 years without cardiac disease: Start at full replacement dose of 1.6 mcg/kg/day 1, 5

For patients >70 years OR with cardiac disease/multiple comorbidities: Start at 25-50 mcg/day and titrate gradually by 12.5-25 mcg every 6-8 weeks 1, 5

Critical Safety Consideration

Before initiating levothyroxine in suspected central hypothyroidism or concurrent adrenal insufficiency, always start corticosteroids first to prevent life-threatening adrenal crisis 1

Monitoring During Treatment

• Recheck TSH and free T4 every 6-8 weeks after any dose adjustment until TSH reaches target range of 0.5-4.5 mIU/L 1, 6, 2
• Once stable, monitor TSH every 6-12 months or when symptoms change 1, 6
• Target TSH within reference range (0.5-4.5 mIU/L) with normal free T4 1

Treatment Algorithm for Hyperthyroidism

Treatment Options Based on Etiology

For Graves' disease or toxic nodular goiter (autonomous thyroid function): 3, 7

• Antithyroid drugs (methimazole preferred; propylthiouracil in first trimester pregnancy) 7, 4
• Radioactive iodine ablation (most widely used in the United States) 7
• Surgical thyroidectomy 7

For thyroiditis (destructive thyrotoxicosis): Observe if mild, or provide supportive care with beta-blockers for symptoms; steroids only in severe cases 3, 4

Treatment Selection Factors

• Graves' disease is preferably treated with antithyroid drugs for 12-18 months, though recurrence occurs in ~50% of patients 4
• Toxic nodular goiter is mostly treated with radioiodine or thyroidectomy 4
• Treatment choice depends on underlying diagnosis, contraindications, severity, and patient preference 7

Management of Subclinical Disease

Subclinical Hypothyroidism (TSH 4.5-10 mIU/L with normal free T4)

Do NOT routinely treat, but monitor TSH every 6-12 months 1

Consider treatment in specific situations: 1

• Symptomatic patients (trial of therapy for 3-4 months with clear evaluation of benefit)
• Positive anti-TPO antibodies (higher progression risk)
• Pregnant or planning pregnancy
• Infertility or goiter present

Subclinical Hyperthyroidism (TSH <0.5 mIU/L with normal free T4 and T3)

Treat patients at highest risk: Those >65 years or with persistent TSH <0.1 mIU/L, due to increased risk of osteoporosis, atrial fibrillation, and cardiovascular mortality 3

Common Pitfalls to Avoid

• Never treat based on a single abnormal TSH value—confirm with repeat testing, as transient elevations are common 1
• Never start thyroid hormone before ruling out adrenal insufficiency in suspected central hypothyroidism—this can precipitate adrenal crisis 1
• Avoid excessive levothyroxine dosing—approximately 25% of patients are unintentionally overtreated with fully suppressed TSH, increasing risks for atrial fibrillation (3-5 fold), osteoporosis, fractures, and cardiovascular complications 1, 2
• Do not adjust levothyroxine doses more frequently than every 6-8 weeks—steady state requires this interval 1
• In elderly patients with cardiac disease, never start at full replacement dose—this can precipitate myocardial infarction, heart failure, or fatal arrhythmias 1

Special Populations

Pregnancy

• Increase pre-pregnancy levothyroxine dose by 25-50% immediately upon pregnancy confirmation 1, 6, 5
• Monitor TSH every 4 weeks until stable, then at minimum once per trimester 6
• Target TSH <2.5 mIU/L in first trimester 1
• Untreated hypothyroidism increases risk of preeclampsia, low birth weight, and neurodevelopmental effects in offspring 1, 5

Elderly Patients

• Start levothyroxine at 25-50 mcg/day regardless of calculated weight-based dose 1, 5
• Consider slightly higher TSH targets (up to 5-6 mIU/L may be acceptable in very elderly patients) to avoid overtreatment risks 1
• Monitor closely for cardiac complications including angina, arrhythmias, and heart failure 1