Hashimoto Thyroiditis

Background

• Hashimoto thyroiditis is a chronic autoimmune process, occurring in all age groups, characterized by lymphocytic infiltration of the thyroid gland, which usually results in a painless goiter.
• While the exact cause is unknown, it is thought to develop from a combination of environmental and immunological factors in patients with underlying genetic susceptibility. It can also be part of a rare autoimmune polyendocrinopathy syndrome.
• The disease course may vary from euthyroidism to hypothyroidism, and occasionally hyperthyroidism.
• Serious but rare complications include steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT) and thyroid lymphoma.

Evaluation

• Suspect Hashimoto thyroiditis in a patient with a painless goiter (usually symmetrical with a diffusely pebbly texture) and/or hypothyroidism (though occasionally hyperthyroidism with concomitant Graves' disease), or ultrasound findings suggestive of thyroiditis.
• Assess thyroid function by measuring serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) (Strong recommendation). Consider measuring free triiodothyronine (FT3) only in patients with low TSH and normal FT4 to assess for hyperthyroidism.
• Measure antithyroid peroxidase antibodies (TPOAb) (Weak recommendation) and consider other antithyroid antibodies if autoimmune (Hashimoto) thyroiditis is still suspected despite negative TPOAb testing. Autoimmune thyroiditis is confirmed via elevated levels of ≥ 1 of the following:
  • TPOAb - present in 90%-95% of patients (if present, further antibody testing is unnecessary)
  • antithyroglobulin antibodies (TgAb) - present in 60%-80% of patients
  • TSH receptor-blocking antibodies - reported in about 10% of patients
• Consider other possible causes of painless thyroiditis, such as postpartum- or medication-induced thyroiditis (for example due to lithium, amiodarone, or interferon alfa).
• Further testing is usually not indicated unless malignancy is suspected.
  • Consider thyroid ultrasound for a palpable nodule, multinodular goiter, or a goiter associated with cervical adenopathy.
  • Consider fine-needle aspiration for suspicious or rapidly growing thyroid nodule.

Management

• Levothyroxine (L-thyroxine) is drug of choice for thyroid hormone replacement (Strong recommendation).
• Indications for levothyroxine:
  • All patients with overt hypothyroidism (characterized by elevated TSH and low FT4), including pregnant women, should be treated with levothyroxine (Strong recommendation).
  • For nonpregnant patients with subclinical hypothyroidism (characterized by mildly elevated TSH, normal FT4, and normal FT3), consider levothyroxine if thyroid stimulating hormone (TSH) levels ≥ 10 milliunits/L, especially with positive antithyroid peroxidase antibodies (TPOAb) (Weak recommendation).
  • For pregnant women or those planning pregnancy who have subclinical hypothyroidism, especially if any current or past history of positive antithyroid peroxidase antibody, consider treatment with levothyroxine (Weak recommendation).
• Levothyroxine oral dosing:
  • In adults with overt hypothyroidism:
    • Consider starting with full replacement dose of 1.6 mcg/kg/day (100-125 mcg/day) in typical adults (Weak recommendation).
    • Consider lower starting doses (12.5-50 mcg/day) for patients > 50 years old or with concomitant coronary artery disease (Weak recommendation).
    • In pregnant women, increase levothyroxine dose by 25%-30% as soon as pregnancy is known (Strong recommendation).
  • In children (dosing by age) with overt hypothyroidism:
    • 0-3 months 10-15 mcg/kg/day
    • 3-6 months 8-10 mcg/kg/day
    • 6-12 months 6-8 mcg/kg/day
    • 1-5 years 5-6 mcg/kg/day
    • 6-12 years 4-5 mcg/kg/day
    • 13-17 years 2-3 mcg/kg/day before puberty and growth complete, then 1.6 mcg/kg/day
  • In adult patients with subclinical hypothyroidism, consider levothyroxine 25-75 mcg/day, depending on degree of TSH elevation (Weak recommendation).
• Follow-up:
  • In patients treated with levothyroxine, monitor TSH levels at 4-6 weeks after starting treatment, changing dose, or starting other drugs that change levothyroxine bioavailability or metabolism; then 6 months after stable dose achieved, then every 12 months (Strong recommendation).
  • Do not monitor antibody levels because they are not reduced by levothyroxine.
  • In patients not receiving treatment, monitor TSH levels at baseline, 6 months, and then every 1-2 years or for new symptoms of hypothyroidism.