Can an upper respiratory infection (URI) with throat swelling cause hyperthyroidism in a patient, particularly those with a history of thyroid disease or specific demographics such as women or older adults?

Can URI with Throat Swelling Cause Hyperthyroidism?

No, an upper respiratory infection (URI) with throat swelling does not directly cause hyperthyroidism, but it can trigger subacute thyroiditis, which presents with transient thyrotoxicosis (hyperthyroid symptoms) that mimics true hyperthyroidism. This is a critical distinction because the management and prognosis differ substantially from primary hyperthyroid disorders.

The Key Pathophysiologic Link

Subacute thyroiditis (also called de Quervain's thyroiditis) is a viral-triggered inflammatory thyroid condition that typically develops 2-8 weeks after an upper respiratory infection. 1, 2 This condition causes:

• Destructive release of preformed thyroid hormone from inflamed thyroid tissue, creating a thyrotoxic state (not true hyperthyroidism from overproduction) 1
• Painful, tender thyroid gland with anterior neck pain that may radiate to the jaw or ears 1, 3
• Elevated thyroid hormones (FT3, FT4) with suppressed TSH during the acute phase 1
• Markedly elevated thyroglobulin levels (often >100 pg/mL) 1
• Reduced or absent radioiodine uptake on thyroid scintigraphy, distinguishing it from Graves' disease 1

Clinical Presentation Pattern

The typical sequence unfolds as follows:

1. Initial URI phase: Patient has upper respiratory symptoms (sore throat, congestion, fever) that resolve or improve 1, 2, 4
2. Latent period: 2-8 weeks pass with relative wellness 2
3. Thyroiditis phase: New onset of anterior neck pain, fever recurrence, and hyperthyroid symptoms (tremors, palpitations, fatigue, heat intolerance) 1, 2, 3

This biphasic pattern is the diagnostic clue—if a patient develops fever and neck pain after apparent recovery from URI, subacute thyroiditis must be considered. 2, 3

Critical Diagnostic Features

Physical examination reveals:

• Diffusely tender, painful thyroid gland on palpation 1, 3
• Cervical or submandibular lymphadenopathy may be present 1
• Signs of thyrotoxicosis: tremor, tachycardia, warm skin 1
• Elevated inflammatory markers: ESR typically >50 mm/hr, elevated CRP 3

Important pitfall: Subacute thyroiditis can occasionally present with normal thyroid function tests initially, manifesting only as fever and elevated inflammatory markers. 3 Always consider thyroid imaging (ultrasound or PET scan) if pyrexia of unknown origin follows URI, even with normal TSH.

Why This Matters for Patient Outcomes

Recognizing subacute thyroiditis is critical because:

• Thyrotoxicosis can worsen concurrent respiratory distress from the original viral infection 1
• Treatment differs fundamentally: corticosteroids (prednisone 25-40 mg daily, tapered over 4-6 weeks) provide rapid symptom relief, whereas antithyroid drugs used for Graves' disease are ineffective and inappropriate 1, 3
• The condition is self-limiting but may last 2-6 months with potential for transient hypothyroidism during recovery 1
• Long-term sequelae include permanent hypothyroidism in approximately 5-15% of cases, requiring lifelong monitoring 1

Specific Viral Associations

Recent evidence links subacute thyroiditis to:

• SARS-CoV-2 (COVID-19): Multiple case reports document subacute thyroiditis 4-8 weeks post-COVID infection 1, 2
• Traditional URI viruses: Coxsackievirus, adenovirus, mumps, influenza 2

The viral trigger creates an antigen that initiates the inflammatory thyroid response. 2

Management Algorithm

When a patient presents with neck pain/swelling and hyperthyroid symptoms following URI:

1. Obtain thyroid function tests: TSH, FT4, FT3, thyroglobulin 1
2. Check inflammatory markers: ESR, CRP 3
3. Perform thyroid ultrasound: Shows hypoechoic, heterogeneous gland 3
4. Consider thyroid scintigraphy if diagnosis unclear: Reduced uptake confirms subacute thyroiditis vs. increased uptake in Graves' disease 1
5. Initiate corticosteroid therapy (prednisone 25-40 mg daily) if diagnosis confirmed, with gradual taper over 4-6 weeks 1, 3
6. Provide symptomatic management: Beta-blockers for palpitations/tremor if needed 1
7. Monitor thyroid function every 4-6 weeks during recovery and for 6-12 months after resolution to detect permanent hypothyroidism 1

What NOT to Do

• Do not prescribe antithyroid medications (methimazole, propylthiouracil)—they are ineffective because this is destructive thyroiditis, not hormone overproduction 1
• Do not attribute all neck swelling to simple pharyngitis—always palpate the thyroid when neck symptoms persist or recur after URI 2
• Do not assume normal TSH excludes thyroid pathology in the setting of post-URI fever and neck pain 3