What is the workup and treatment for autoimmune hypothyroidism?

Workup and Treatment of Autoimmune Hypothyroidism

Diagnostic Workup

The diagnosis of autoimmune hypothyroidism requires measurement of both TSH and free T4 levels, with anti-thyroid antibodies testing to confirm autoimmune etiology. 1

Initial Laboratory Testing

• TSH and Free T4: Essential first-line tests
  • Elevated TSH with low Free T4 indicates primary hypothyroidism
  • Low TSH with low Free T4 suggests central hypothyroidism (requires different evaluation) 1
• Anti-thyroid antibodies:
  • Anti-thyroid peroxidase (TPO) antibodies
  • Anti-thyroglobulin antibodies
  • Positive antibodies confirm autoimmune etiology (Hashimoto's thyroiditis) 1

Additional Testing

• Complete blood count: To assess for anemia (common in hypothyroidism)
• Lipid profile: Hypothyroidism often causes hypercholesterolemia
• Liver function tests: To establish baseline before treatment
• Serum electrolytes: To check for hyponatremia

Imaging

• No routine imaging is required for diagnosis of autoimmune hypothyroidism 1
• Thyroid ultrasound is not necessary for diagnosis but may be considered if:
  • Thyroid nodules are palpated on physical examination
  • Asymmetric thyroid enlargement is present
  • Compressive symptoms are reported

Treatment Protocol

Levothyroxine Replacement Therapy

• Initial dosing:

  • Adults under 60 without cardiac disease: 1.6 mcg/kg/day 2
  • Adults over 60 or with cardiac disease: Start with 12.5-50 mcg/day and titrate slowly 3

• Monitoring and Dose Adjustment:

  • Check TSH 6-8 weeks after initiating therapy or changing dose 2
  • Target TSH within normal reference range
  • Once stable, monitor TSH every 6-12 months 2
  • Free T4 can help interpret abnormal TSH levels during therapy 1

Special Populations

Pregnant Patients

• Increase levothyroxine dose by 30% (approximately two extra doses per week) as soon as pregnancy is confirmed 2, 3
• Monitor TSH and Free T4 each trimester
• Return to pre-pregnancy dose immediately after delivery 2

Elderly Patients

• Start with lower dose (12.5-50 mcg/day)
• Titrate more slowly to avoid cardiac complications 3
• Monitor for overtreatment (can cause atrial fibrillation and osteoporosis) 1

Management of Complications

Myxedema (Severe Hypothyroidism)

• Requires hospitalization and endocrinology consultation
• IV levothyroxine administration
• Supportive care including hydration and monitoring for bradycardia and hypothermia 1

Subclinical Hypothyroidism

• Treatment recommended if:
  • TSH persistently >10 mIU/L
  • Thyroid antibodies are positive with symptoms
  • Patient is symptomatic 3
• Treatment generally not beneficial for mild subclinical hypothyroidism (TSH <10 mIU/L) without symptoms 3

Common Pitfalls and Caveats

1. Overtreatment: Excessive levothyroxine can cause iatrogenic hyperthyroidism leading to:

   • Atrial fibrillation
   • Osteoporosis
   • Anxiety and insomnia 1

2. Medication Interactions: Several medications can interfere with levothyroxine absorption:

   • Iron and calcium supplements
   • Proton pump inhibitors
   • Aluminum-containing antacids
   • Take levothyroxine on empty stomach, 30-60 minutes before other medications

3. Inadequate Monitoring: Failure to adjust dose based on TSH levels can lead to under or overtreatment

4. Misdiagnosis: Physical examination alone is insufficient for diagnosis of hypothyroidism - laboratory confirmation is essential 4

5. Persistent Symptoms: Despite normalized TSH, some patients may have persistent symptoms requiring evaluation for other causes 3

Remember that autoimmune hypothyroidism often coexists with other autoimmune disorders, so periodic screening for conditions like type 1 diabetes, celiac disease, and adrenal insufficiency is warranted, particularly when symptoms persist despite adequate thyroid replacement 1.