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Thyroiditis: A Complete Guide to Types, Symptoms, Diagnosis, and Treatment

Thyroiditis refers to a group of inflammatory thyroid disorders with diverse causes, clinical courses, and treatments. Accurate classification is essential because management differs significantly across types—what helps one form may harm another.

Major Types of Thyroiditis

1. Hashimoto's Thyroiditis (Chronic Autoimmune Thyroiditis)

  • Cause: Autoimmune destruction mediated by anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies.
  • Course: Gradual progression to hypothyroidism; a transient thyrotoxic phase ("hashitoxicosis") may occur early.
  • Demographics: Women affected 10:1; typical onset 30–50 years; strong family history common.
  • Treatment: Levothyroxine when overtly hypothyroid (TSH >10 mIU/L) or symptomatic with subclinical hypothyroidism (TSH 4.5–10). Monitor if subclinical and asymptomatic.

2. Subacute Thyroiditis (De Quervain's / Granulomatous)

  • Cause: Post-viral inflammation (coxsackievirus, mumps, influenza, COVID-19).
  • Course: Three phases over 3–6 months: thyrotoxic (painful) → hypothyroid → recovery (90–95% recover fully).
  • Symptoms: Neck pain radiating to jaw/ears, fever, fatigue, hyperthyroid symptoms (palpitations, tremor, heat intolerance).
  • Treatment: NSAIDs for pain; beta-blockers for thyrotoxic symptoms; prednisone for severe pain; levothyroxine only if hypothyroid phase is symptomatic.

3. Silent / Painless Thyroiditis

  • Cause: Autoimmune (lymphocytic); postpartum variant is common.
  • Course: Same three phases as subacute but painless; ~20% develop permanent hypothyroidism.
  • Treatment: Beta-blockers for thyrotoxic phase; monitor; treat hypothyroidism if persistent.

4. Postpartum Thyroiditis

  • Timing: 1–12 months postpartum (peak 2–6 months).
  • Incidence: 5–10% of pregnancies; higher with positive TPO antibodies.
  • Course: Thyrotoxic → hypothyroid → recovery (80%); 20–30% permanent hypothyroidism.
  • Screening: TSH at 3 and 6 months postpartum if symptomatic or TPO-positive.
  • Treatment: Symptomatic; levothyroxine if TSH >10 or symptomatic 4.5–10; consider levothyroxine if planning another pregnancy.

5. Drug-Induced Thyroiditis

  • Amiodarone: Causes both destructive (amiodarone-induced thyrotoxicosis type 1/2) and synthetic effects due to high iodine content.
  • Immune checkpoint inhibitors: Can cause hypophysitis or primary thyroiditis.
  • Others: Tyrosine kinase inhibitors, lithium, interferon-α, alemtuzumab.
  • Management: Discontinue offending drug if possible; treat thyrotoxicosis or hypothyroidism as needed.

6. Infectious Thyroiditis

  • Bacterial: Rare; acute suppurative (Staphylococcus, Streptococcus) with abscess risk; requires antibiotics ± drainage.
  • Fungal/Parasitic: Seen in immunocompromised hosts.

7. Radiation Thyroiditis

  • Follows radioactive iodine (RAI) therapy or external beam radiation.
  • Transient thyrotoxicosis from hormone release, followed by hypothyroidism.

Diagnostic Approach

No single test diagnoses thyroiditis; a combination of labs and imaging differentiates types and phases.

TestPurposeTypical Findings by Phase
TSHPrimary screenLow (thyrotoxic) → High (hypothyroid) → Normalize
Free T4 / Free T3Confirm thyroid statusHigh → Low → Normal
Anti-TPO / Anti-TgAutoimmune etiologyPositive in Hashimoto's, silent, postpartum
ESR / CRPInflammation markerElevated in subacute thyroiditis
Thyroid ultrasoundStructure, vascularityHypoechoic, heterogeneous (Hashimoto's); normal/enlarged (subacute)
Radioactive iodine uptake (RAIU)Differentiate thyrotoxic causesLow in destructive thyroiditis; high in Graves' disease

Treatment Principles by Phase

  • Thyrotoxic phase: Beta-blockers (propranolol, atenolol) for symptom control. Do not use antithyroid drugs (methimazole, PTU)—thyroiditis is not synthesis-driven.
  • Hypothyroid phase: Levothyroxine if TSH >10 or symptomatic with TSH 4.5–10; usually temporary (6–12 months).
  • Recovery: Taper levothyroxine; recheck TSH 6–12 weeks after stopping.

Long-Term Outlook

  • Hashimoto's: Lifelong hypothyroidism is typical.
  • Subacute, silent, and postpartum: 80–95% recover; 5–20% develop permanent hypothyroidism.
  • Annual TSH monitoring after recovery.
  • Postpartum thyroiditis recurs in ~70% of subsequent pregnancies if TPO-positive.

Key Distinction: Thyrotoxicosis from thyroiditis shows low RAIU and is self-limited. Graves' disease shows high RAIU and persists. This differentiation prevents inappropriate antithyroid drug use.

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