Thyroiditis

Munima Nasir, MD
Ian P. Downin, MD, MHA

BASICS

Painful or painless inflammation of the thyroid
Painful thyroiditis:
- Subacute granulomatous thyroiditis (de Quervain, giant cell): self-limited; viral URI prodrome, variable symptoms/signs
- Infectious/suppurative thyroiditis: most commonly due to Streptococcus pyogenes, Staphylococcus aureus, Streptococcus pneumoniae, but also fungal, mycobacterial, parasitic; rare
- Radiation-induced thyroiditis: after radioactive iodine or external irradiation
Painless thyroiditis:
- Hashimoto (autoimmune) thyroiditis: chronic, most common cause of hypothyroidism; 90% with high antithyroid peroxidase (TPO) antibodies
- Postpartum thyroiditis (PPT): thyrotoxicosis → hypothyroidism in 1st year after pregnancy/abortion in previously normal women
- Painless (silent) thyroiditis: mild hyperthyroid, small painless goiter, no Graves features
- Riedel thyroiditis: fibrous replacement, compressive symptoms (dyspnea, dysphagia, hoarseness)
- Drug-induced thyroiditis: interferon-α, interleukin-2, amiodarone, kinase inhibitors, lithium

Subacute granulomatous: most common cause of thyroid pain, 3/100,000/yr, female > male (4:1), peak age 40–50
Hashimoto thyroiditis: peak 30–50 yrs, can occur in children, female > male (7:1)
PPT: within 12 months post-pregnancy, 1–18% of pregnancies
Painless thyroiditis: 1–5% of cases, female > male (4:1), peak 30–40 yrs
Reidel thyroiditis: rare, female > male (4:1), highest prevalence 30–60 yrs, incidence 1.06/100,000

Subacute granulomatous: probably viral (COVID-19 included), direct and indirect immune-mediated damage
Hashimoto: autoantibodies via molecular mimicry, triggers include infection, stress, sex steroids, pregnancy, iodine, radiation
PPT: autoimmunity-induced hormone discharge
Painless thyroiditis: autoimmune
Reidel: fibrous replacement, systemic fibrosis
Genetics: CT60 polymorphism, HLA-DR4, DR5, DR6 (white populations)

Subacute granulomatous: viral infection (COVID-19), HLA-B35
Hashimoto: family or personal autoimmune disease, high iodine, smoking, selenium deficiency

Hypothyroid: constipation, heavy periods, fatigue, dry skin, cold intolerance
Hyperthyroid: irritability, heat intolerance, palpitations, sweating, sleep disturbance, lid retraction
Subacute granulomatous: sudden/gradual onset, recent URI, neck/jaw/ear pain, can be painless in COVID-19
Course: classic triphasic (thyrotoxic, hypothyroid, recovery); varies in subtypes

Hashimoto: 90% symmetric, diffuse, firm goiter; 10% atrophy
PPT: painless, small, nontender gland
Reidel: rock-hard, “woody” gland, compressive symptoms (stridor, dysphagia, hoarseness)
Hypothyroid signs: delayed DTR relaxation, alopecia, bradycardia
Hyperthyroid signs: moist skin, hyperreflexia

Simple goiter, iodine deficiency, thyroid cancer, infections, drug-induced thyroid dysfunction, amyloid

Subacute (de Quervain):
- Thyrotoxic phase: ↓TSH, ↑T4, ↑ESR/CRP/WBC, mild anemia
- 25% low antithyroid Abs
- ESR normalizes in hypothyroid phase
- US to rule out cancer
Suppurative (acute):
- Usually euthyroid, can be destructive thyrotoxicosis
- US/CT diagnostic; FNA for confirmation
Hashimoto:
- Anti-TPO Ab: 95%, antithyroglobulin Ab: 60–80%
- US: decreased echogenicity, hypoechoic nodules with echogenic rim
PPT: TPOAb/TgAb; positive 1st trimester = higher risk
- Distinguish from Graves: TSH receptor Ab, high RAIU
- Repeat TSH 4–8 weeks after thyrotoxic phase, and annually if history of PPT
Painless thyroiditis: 5–20% have 3–4 month thyrotoxic phase, normalizes in 12 months, ~50% anti-TPO positive
Reidel: elevated thyroglobulin/TPO Ab, ↑CRP/ESR, possible hypocalcemia
Drug-induced: variable labs depending on drug; lithium → hypothyroid
General: TSH, free T4, T3, antithyroid antibodies
Imaging: US (heterogeneous, hypoechoic), RAIU scan (decreased in all thyroiditis, not for Hashimoto), urine iodine measurement
FNAC: dominant nodule in Hashimoto, open biopsy for Riedel if needed

Thyrotoxic/symptomatic: propylthiouracil/propranolol (not used in PPT/painless)
Pregnancy/trying to conceive + ↑TSH: thyroid replacement

Subacute granulomatous:
- β-blockers, NSAIDs
- Prednisone 40 mg/day × 1–2 weeks, taper 2–4 weeks (severe cases)
- Levothyroxine for hypothyroid phase, discontinue 3–6 months after normalization
Suppurative (acute): systemic antibiotics, abscess drainage, excision/occlusion if sinus tract present
Hashimoto: Levothyroxine 1.6–1.8 μg/kg
PPT: manage by phase; metoprolol/propranolol for lactation; antithyroid drugs not recommended
- Taper levothyroxine 12 months postpartum, monitor TSH q6–8w
- Avoid tapering if pregnant/trying to conceive
Painless thyroiditis: β-blocker for hyperthyroid symptoms, corticosteroids for severe hyperthyroid phase (rare), antithyroid drugs not needed
Reidel: no consensus, glucocorticoids, treat hypothyroidism (levothyroxine), hypoparathyroidism (Ca/calcitriol), debulking surgery for obstruction
Drug-induced: discontinue offending agent

Pregnancy: 131I contraindicated in breastfeeding

Meftah E, Rahmati R, Zari Meidani F, et al. Subacute thyroiditis following COVID-19: a systematic review. Front Endocrinol (Lausanne). 2023;14:1126637.
Popescu M, Ghemigian A, Vasile CM, et al. The new entity of subacute thyroiditis amid the COVID-19 pandemic: from infection to vaccine. Diagnostics (Basel). 2022;12(4):960.
Ross DS, Burch HB, Cooper DS, et al. 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid. 2016;26(10):1343-1421.
Massimo R, Angeletti D, Fiore M, et al. Hashimoto's thyroiditis: an update. Autoimmun Rev. 2020;19(10):102649.
Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the ATA for thyroid disease in pregnancy. Thyroid. 2017;27(3):315-389.

Codes:

End of note