What are the diagnostic criteria and treatment options for hypothyroidism?

Diagnosis and Treatment of Hypothyroidism

Hypothyroidism is diagnosed by elevated TSH with low free T4 levels, with treatment consisting of levothyroxine replacement therapy to normalize TSH levels and alleviate symptoms.

Diagnostic Criteria

Initial Testing

• If hypothyroidism is suspected, measure TSH first, followed by free T4 to differentiate between subclinical and overt hypothyroidism 1
• Repeat abnormal results in 2 weeks to 3 months before initiating treatment to confirm diagnosis 2, 1
• Morning testing is preferred for more accurate results, especially when assessing adrenal function simultaneously 1

Interpretation of Laboratory Results

• Overt primary hypothyroidism: Elevated TSH with low free T4 3
• Subclinical hypothyroidism: Elevated TSH with normal free T4 (prevalence 4-10% in general population) 2, 1
• Central hypothyroidism: Low or inappropriately normal TSH with low free T4 (due to pituitary or hypothalamic dysfunction) 2

Additional Testing to Consider

• Anti-thyroid peroxidase (anti-TPO) antibodies to identify autoimmune etiology (Hashimoto's thyroiditis), which predicts higher risk of developing overt hypothyroidism (4.3% per year vs. 2.6% per year in antibody-negative individuals) 2, 1
• Lipid profile testing as hypothyroidism can affect cholesterol levels 2, 1

Treatment Options

Levothyroxine Therapy

• Overt hypothyroidism: All patients should receive levothyroxine replacement therapy 3, 4
• Subclinical hypothyroidism: Treatment recommended for:
  • TSH >10 mIU/L 2, 4
  • Pregnant women or women planning pregnancy 4
  • Symptomatic patients 4
  • Patients with positive anti-TPO antibodies or goiter 4
• Initial dosing:
  • For most young patients: 1.5-1.8 mcg/kg/day 5
  • For elderly patients (>60 years) or those with cardiovascular disease: Start with lower dose (12.5-50 mcg/day) 5, 6
  • For pregnant women: Increase weekly dosage by 30% (take one extra dose twice weekly) 5

Monitoring and Dose Adjustment

• Check TSH 6-8 weeks after initiating therapy or changing dose 3
• Target TSH: 0.5-2.0 mIU/L for primary hypothyroidism 4
• For central hypothyroidism, maintain free T4 in upper half of normal range 4
• Annual monitoring once target levels achieved 3

Special Populations

• Elderly: Start with lower doses due to increased risk of cardiovascular complications 6
• Pregnancy: Prompt treatment essential; monitor TSH regularly and adjust dose as needed 6
• Children: Rapid restoration of normal T4 levels is essential to prevent adverse effects on cognitive development 6

Common Pitfalls to Avoid

• Overtreatment: Associated with increased risk of atrial fibrillation and osteoporosis 4
• Undertreatment: Can lead to persistent symptoms and increased cardiovascular risk 3
• Medication interactions: Certain medications can interfere with levothyroxine absorption 4
• Misdiagnosis of subclinical hypothyroidism: Not all patients with TSH between 4.5-10 mIU/L require treatment, especially if asymptomatic 2, 1
• Initiating thyroid hormone before ruling out adrenal insufficiency: In patients with both adrenal insufficiency and hypothyroidism, steroids should always be started prior to thyroid hormone to avoid adrenal crisis 2

Clinical Presentation

• Common symptoms include fatigue (68-83%), weight gain (24-59%), cold intolerance, constipation, dry skin, and cognitive issues (45-48%) 3, 7
• Untreated hypothyroidism can lead to serious complications including heart failure, myxedema coma (with mortality rate up to 30%), and in pregnant women, increased risk of miscarriage 3
• Hashimoto's thyroiditis is the most common cause of primary hypothyroidism in iodine-sufficient areas (up to 85% of cases) 3, 8

By following these diagnostic criteria and treatment guidelines, clinicians can effectively manage hypothyroidism and prevent its complications, improving patients' quality of life and reducing mortality risk.