What is the approach to investigating acute thyroiditis?

Investigation of Acute Thyroiditis

The investigation of acute thyroiditis should begin with thyroid function tests (TSH, free T4, free T3), inflammatory markers (CRP, ESR), and thyroid antibody testing, followed by imaging with ultrasound as the first-line modality to evaluate thyroid morphology and blood flow patterns. 1, 2

Clinical Presentation and Initial Assessment

Acute thyroiditis presents in several forms, each requiring specific diagnostic approaches:

• Acute suppurative thyroiditis:

  • Presents with fever, severe neck pain, erythema, and tenderness
  • Often occurs in immunocompromised patients or those with anatomical defects
  • May progress to abscess formation if untreated 3

• Subacute granulomatous thyroiditis (de Quervain's):

  • Characterized by anterior neck pain, often following upper respiratory infection
  • Typically self-limited but painful 4

• Subacute lymphocytic (silent) thyroiditis:

  • Usually painless
  • Often occurs in postpartum period
  • Autoimmune in origin 5

Diagnostic Algorithm

Step 1: Laboratory Testing

• Thyroid function tests:

  • TSH, free T4, free T3 to determine thyroid status
  • Most forms of thyroiditis follow a triphasic pattern:
    • Initial hyperthyroidism (thyrotoxicosis) - low TSH, high free T4/T3
    • Followed by hypothyroidism - high TSH, low free T4/T3
    • Eventually normal function may return 1

• Inflammatory markers:

  • Elevated ESR and CRP in subacute granulomatous thyroiditis
  • May be normal in lymphocytic thyroiditis 5

• Thyroid antibodies:

  • Thyroid peroxidase (TPO) antibodies - elevated in Hashimoto's thyroiditis
  • Thyroglobulin antibodies - may be elevated in autoimmune thyroiditis
  • TSH receptor antibodies (TRAb) - to rule out Graves' disease 2

Step 2: Imaging Studies

• Thyroid ultrasound (first-line imaging):

  • Evaluates thyroid morphology and identifies nodules
  • Doppler assessment can differentiate causes of thyrotoxicosis:
    • Increased blood flow: Graves' disease
    • Decreased blood flow: Destructive thyroiditis 2
  • Can identify abscess formation in suppurative thyroiditis 3

• Radionuclide uptake and scan:

  • Radioiodine uptake (RAIU) or Technetium-99m scan
  • Decreased uptake in destructive thyroiditis (distinguishing from Graves' disease)
  • I-123 preferred over I-131 due to superior imaging quality 2

• CT/MRI:

  • Not routinely needed for thyroiditis
  • Consider if suspecting abscess, malignancy, or retropharyngeal extension 2

Step 3: Additional Testing Based on Clinical Suspicion

• Fine needle aspiration (FNA):

  • Indicated when suppurative thyroiditis is suspected
  • Provides material for culture and sensitivity testing 3

• Blood cultures:

  • Important in acute suppurative thyroiditis to identify causative organism 3

Management Considerations Based on Diagnosis

• Acute suppurative thyroiditis:

  • Requires antibiotics and possible surgical drainage 3

• Subacute granulomatous thyroiditis:

  • NSAIDs for pain control
  • Corticosteroids for severe symptoms
  • Beta-blockers for thyrotoxic symptoms 4

• Subacute lymphocytic thyroiditis:

  • Monitoring thyroid function
  • Beta-blockers for thyrotoxic symptoms
  • Consider levothyroxine if TSH >10 mIU/L or symptomatic with TSH 4-10 mIU/L 4

Follow-up Recommendations

• Regular monitoring of thyroid function every 4-6 weeks until stabilized
• Long-term surveillance recommended as some forms may progress to permanent hypothyroidism 1

Pitfalls to Avoid

• Misdiagnosing subacute thyroiditis as Graves' disease (both can present with thyrotoxicosis)
• Failing to consider suppurative thyroiditis in immunocompromised patients with neck pain and fever
• Overlooking drug-induced thyroiditis (amiodarone, immune checkpoint inhibitors, interleukin-2, interferon-alfa) 2, 1
• Delaying treatment of suppurative thyroiditis, which can lead to life-threatening complications 3

By following this systematic approach to investigating acute thyroiditis, clinicians can accurately diagnose the specific type and initiate appropriate treatment to reduce morbidity and improve patient outcomes.