What are the diagnostic tests and treatment options for viral thyroiditis?

Diagnostic Testing for Viral Thyroiditis

Diagnose viral (subacute) thyroiditis with the combination of anterior neck pain/tenderness, suppressed TSH with elevated free T4 or T3, markedly elevated thyroglobulin, elevated ESR, and low radioactive iodine uptake on thyroid scanning. 1, 2

Clinical Presentation

Viral thyroiditis typically follows an upper respiratory infection by several weeks and presents with: 1, 3

• Anterior neck pain and tenderness (distinguishes it from painless thyroiditis)
• Symptoms of thyrotoxicosis: palpitations, tremors, heat intolerance, weight loss, anxiety 4
• Fever may be present 3
• Enlarged, tender cervical lymph nodes 3
• Diffusely tender goiter on palpation 3

Essential Diagnostic Tests

First-Line Laboratory Tests

• TSH and free T4 (or total T3): TSH will be suppressed (low/normal) with elevated free T4 or T3 during the thyrotoxic phase 4
• Thyroglobulin: Markedly elevated (often >100 pg/mL), reflecting thyroid follicular destruction 2, 3
• ESR: Significantly elevated, distinguishing subacute thyroiditis from other causes 2, 5

Confirmatory Imaging

• Radioactive iodine uptake (RAIU) scan or Technetium-99m pertechnetate scan: Shows markedly reduced or absent uptake, confirming destructive thyroiditis rather than Graves' disease 4, 2, 3
  • Use Tc-99m if recent iodinated contrast was administered 4

Additional Tests to Rule Out Alternative Diagnoses

• Thyroid peroxidase (TPO) antibodies: Typically negative or low-titer (helps exclude autoimmune thyroiditis) 4
• TSH receptor antibodies (TRAb) or thyroid stimulating immunoglobulin (TSI): Negative (excludes Graves' disease) 4

Diagnostic Algorithm

1. Suspect viral thyroiditis in patients with anterior neck pain/tenderness following upper respiratory infection 1, 2, 3

2. Order initial labs: TSH, free T4, thyroglobulin, ESR 2, 3

3. If TSH suppressed with elevated free T4 and markedly elevated thyroglobulin/ESR: Proceed to RAIU or Tc-99m scan 2, 3

4. If uptake is low/absent: Diagnosis confirmed; begin symptomatic treatment 4, 2

5. If uptake is normal/high: Consider Graves' disease; order TRAb/TSI 4

Treatment Approach

Thyrotoxic Phase (Initial 1-2 Months)

• High-dose NSAIDs or aspirin for thyroid pain and inflammation 1, 5
• Prednisone 25-40 mg/day (gradually tapered) for severe pain unresponsive to NSAIDs 3, 5
• Non-selective beta-blockers (preferably with alpha-blocking capacity like carvedilol) for symptomatic thyrotoxicosis 4
• Do NOT use antithyroid drugs (methimazole/PTU) as this is destructive, not overproduction 1, 6

Monitoring and Subsequent Phases

• Repeat thyroid function tests every 2-3 weeks to detect transition to hypothyroidism 4
• Hypothyroid phase typically occurs 1 month after thyrotoxic phase and may be transient or permanent 4, 1
• Initiate levothyroxine when TSH becomes elevated with low free T4 4, 1

Critical Pitfalls to Avoid

• Do not confuse with Graves' disease: Both cause thyrotoxicosis, but viral thyroiditis has neck pain, elevated ESR, and low RAIU 4, 2
• Do not delay RAIU/scan: This is essential to distinguish destructive thyroiditis from hyperthyroidism requiring antithyroid drugs 2
• Do not miss the hypothyroid transition: Most patients develop permanent hypothyroidism requiring lifelong replacement 4, 1
• Consider COVID-19 association: SARS-CoV-2 can trigger subacute thyroiditis; maintain high clinical suspicion in this context 3

When to Refer to Endocrinology

Endocrinology consultation is recommended for all cases of confirmed thyroiditis, particularly if diagnosis is uncertain, symptoms are severe, or hypothyroidism develops 4