Key Facts

Thyroiditis encompasses several inflammatory conditions with different aetiologies but a common pattern of transient thyroid hormone release. The uptake scan showing low uptake is key to distinguishing thyroiditis from other causes of thyrotoxicosis.

Epidemiology

Subacute thyroiditis: incidence ~5 per 100,000/year; F:M 3:1; peak age 30-50. Postpartum thyroiditis: ~5-10% of postpartum women. Hashimoto: commonest cause of hypothyroidism (covered separately).

Aetiology

Subacute: presumed viral (often post-URTI; coxsackievirus, adenovirus, mumps). HLA-B35 association. Postpartum/silent: autoimmune (anti-TPO positive). Drug-induced: amiodarone (type 2), checkpoint inhibitors, lithium.

Pathophysiology

Thyroiditis causes destruction of thyroid follicular cells → release of preformed T4 and T3 into circulation (thyrotoxic phase). As stores are depleted and the gland is damaged → hypothyroid phase. Most recover as inflammation resolves and thyroid regenerates, but some develop permanent hypothyroidism.

Subacute (de Quervain) Thyroiditis

• Painful, tender, firm thyroid (often unilateral initially, migrating)
• Systemic: fever, malaise, myalgia
• Thyrotoxic phase (weeks 1-4): palpitations, weight loss, tremor
• Hypothyroid phase (weeks 4-12): fatigue, weight gain
• Recovery phase: euthyroid by 3-6 months (~95% recover fully)
• Preceded by viral URTI in 2-8 weeks

Postpartum Thyroiditis

• 1-6 months postpartum: transient thyrotoxicosis (often mild, may be missed)
• 3-12 months postpartum: hypothyroid phase (more symptomatic; fatigue, depression, weight gain)
• ~80% recover; ~20% develop permanent hypothyroidism
• Associated with anti-TPO antibodies

Red Flags

• Severe pain unresponsive to NSAIDs → consider acute suppurative thyroiditis (rare, bacterial)
• Thyrotoxicosis misdiagnosed as Graves → antithyroid drugs are ineffective and inappropriate

Bloods

• TFTs: thyrotoxic phase (suppressed TSH, raised T4/T3); hypothyroid phase (raised TSH, low T4)
• ESR/CRP: markedly raised in subacute thyroiditis (ESR often >50)
• Anti-TPO: positive in postpartum/silent thyroiditis; may be positive in subacute
• TRAb: negative (distinguishes from Graves)

Imaging

• Thyroid uptake scan: low/absent uptake in thyrotoxic phase — KEY diagnostic feature (vs diffuse high uptake in Graves)
• USS thyroid: diffuse hypoechogenicity; may show focal areas of inflammation

Subacute Thyroiditis

• Thyrotoxic phase: beta-blockers (propranolol 40-80mg TDS) for symptom control; NO antithyroid drugs
• Pain: NSAIDs (ibuprofen 400mg TDS, naproxen 500mg BD); if insufficient: prednisolone 30-40mg/day, taper over 4-8 weeks
• Hypothyroid phase: levothyroxine if symptomatic (temporary — reassess at 6-12 months)
• Recovery: most euthyroid by 3-6 months; ~5% develop permanent hypothyroidism

Postpartum Thyroiditis

• Thyrotoxic phase: beta-blockers if symptomatic; NO antithyroid drugs
• Hypothyroid phase: levothyroxine if symptomatic or planning pregnancy (may be temporary)
• Monitoring: TFTs every 4-8 weeks during active phases
• Long-term: annual TFTs (20% develop permanent hypothyroidism)

Referral Criteria

• Endocrinology: diagnostic uncertainty, severe thyroiditis, recurrent episodes

Subacute thyroiditis: self-limiting; ~95% recover full thyroid function by 6-12 months; ~5% permanent hypothyroidism; recurrence rare (~2%). Postpartum thyroiditis: ~80% recover; ~20% permanent hypothyroidism (higher if anti-TPO positive, higher titres). Postpartum thyroiditis recurs in ~70% of subsequent pregnancies.

Thyroiditis — Typical Triphasic Course

Thyroid Uptake Scan Patterns