Thyroiditis

Description

• Inflammatory dysfunction of the thyroid gland
• Painful thyroiditis:
  • Subacute granulomatous thyroiditis—nonsuppurative thyroiditis, de Quervain thyroiditis, giant cell thyroiditis
  • Infectious/suppurative thyroiditis is most commonly associated with Streptococcus and Staphylococcus spp. but can be due to fungal, mycobacterial, or parasitic thyroid infections. Radiation-induced thyroiditis: from radioactive iodine therapy (1%) or external irradiation
• Painless thyroiditis
  • Hashimoto (autoimmune) thyroiditis: most common etiology of chronic hypothyroidism; 90% of patients with high-serum antithyroid peroxidase (TPO) antibodies
  • Postpartum thyroiditis (PPT): thyrotoxicosis followed by hypothyroidism in the 1st year postpartum or after spontaneous/induced abortion
  • Painless (silent) thyroiditis: mild hyperthyroidism
  • Riedel (fibrous) thyroiditis: rare inflammatory process involving the thyroid and surrounding cervical tissues
  • Drug-induced: interferon-α, interleukin-2, amiodarone, kinase inhibitors, or lithium
  • Radiation-induced: from radioactive iodine therapy (1%) or external irradiation

Epidemiology

• Subacute granulomatous thyroiditis: most common cause of thyroid pain; peaks during summer; incidence: 3/100,000/year; female > male (4:1); peak age: 40 to 50 years
• Hashimoto thyroiditis (HT): peak onset 30 to 50 years of age; can occur in children; female > male (7:1)
• PPT: occurs within 12 months of pregnancy in 1–18% of pregnancies
• Painless (silent) thyroiditis: accounts for 1–5% of cases; female > male (4:1) with peak age 30 to 40 years; common in areas of iodine sufficiency
• Riedel thyroiditis: female > male (4:1); highest prevalence age 30 to 60 years; rare with estimated incidence of 1.06 cases per 100,000 patients

Etiology and Pathophysiology

• Subacute granulomatous thyroiditis: probably viral; can be associated with COVID-19 infection; the mechanism of thyroid injury can be due to direct destruction of thyroid tissue, as well as indirect immune-mediated responses, medicines used to treat COVID-19, and less frequently COVID-19 vaccinations (1).
• Hashimoto disease: Antithyroid antibodies may be produced in response to an environmental antigen and cross-react with thyroid proteins (molecular mimicry). Precipitating factors include infection, stress, sex steroids, pregnancy, iodine intake, and radiation exposure.
• PPT: autoimmunity-induced discharge of preformed hormone from the thyroid
• Painless (silent) thyroiditis: autoimmune
• Riedel (fibrous) thyroiditis: rare inflammatory process involving the thyroid and surrounding cervical tissues; associated with various forms of systemic fibrosis

Risk Factors

• Subacute granulomatous thyroiditis: recent viral respiratory infection, such as COVID-19 infection, or HLA-B35
• Hashimoto disease: family/personal history of thyroid/autoimmune disease, high iodine intake, cigarette smoking, selenium deficiency

General Prevention

Emerging evidence may support vitamin D or selenium supplementation, but more research is needed (2).