Are patients with euthyroid Hashimoto's (a condition where the thyroid gland is underactive due to an autoimmune disease) experiencing flare-ups during post or long Covid-19?

Hashimoto's Thyroiditis Flare-ups in Post-COVID and Long COVID

Yes, patients with euthyroid Hashimoto's thyroiditis are experiencing flare-ups during post-COVID and long COVID periods, with evidence showing increased anti-thyroid antibody titers and new-onset thyroid dysfunction in previously stable patients. 1

Thyroid Dysfunction in COVID-19 and Long COVID

Acute Phase Changes

• During acute COVID-19 infection:
  • 56.4% of patients show thyroid dysfunction on admission 1
  • Most common pattern is non-thyroidal illness syndrome (NTIS) 1
  • TSH and T3 levels are often suppressed, correlating with disease severity 2, 3
  • Severe COVID-19 is associated with significantly lower free T3 levels (p=0.001) 1

Post-COVID Recovery Phase

• After COVID-19 recovery:
  • Significant increases in anti-thyroid peroxidase (TPO) and anti-thyroglobulin antibody titers (p<0.001) 4
  • 16 out of 82 patients with initially negative anti-TPO showed significant increases in antibody titers 4
  • 4 patients became anti-TPO positive who were previously negative 4
  • Some patients develop new-onset or persistent subclinical hypothyroidism during the 6-month post-COVID period 1

Hashimoto's-Specific Findings

• Case reports document Hashimoto's thyroiditis developing 6 weeks after COVID-19 infection in previously healthy individuals 5
• Risk factors for post-COVID thyroid autoimmunity include:
  • Worse baseline COVID-19 clinical severity (p=0.018) 4
  • Elevated C-reactive protein during hospitalization (p=0.033) 4
  • Higher baseline anti-TPO titers (p=0.005) 4

Monitoring and Management Recommendations

Recommended Monitoring

• Complete thyroid function panel (TSH, free T3, free T4) 6
• Anti-thyroid antibodies (anti-TPO, anti-Tg) 4
• Follow-up testing at:
  • 3 months post-COVID 4
  • 6 months post-COVID 1
  • Longer follow-up for patients with elevated antibodies

Clinical Manifestations to Monitor

• Fatigue and weakness (may be difficult to distinguish from long COVID symptoms) 7
• New or worsening cognitive dysfunction (brain fog) 7
• Sleep disturbances 7
• Exercise intolerance 7
• Changes in medication requirements for previously stable patients

Pathophysiological Mechanisms

The connection between COVID-19 and Hashimoto's flare-ups appears to involve:

• Immune dysregulation triggered by SARS-CoV-2 infection 6
• Possible molecular mimicry between viral and thyroid antigens 5
• Systemic inflammatory response affecting thyroid function 4
• Endothelial dysfunction and microvascular changes affecting thyroid perfusion 7

Important Clinical Considerations

• Do not attribute all post-COVID symptoms to long COVID without evaluating thyroid function
• Patients with pre-existing Hashimoto's (even if euthyroid) require close monitoring after COVID-19
• The temporal relationship between COVID-19 and thyroid dysfunction strongly suggests a causal link 5
• Thyroid dysfunction may manifest weeks to months after the acute COVID-19 phase 5, 1

Pitfalls to Avoid

• Assuming normal TSH alone rules out thyroid dysfunction in post-COVID patients
• Attributing all fatigue symptoms to long COVID without thyroid evaluation
• Failing to monitor thyroid antibodies even when thyroid function tests appear normal
• Missing subclinical hypothyroidism that may develop during the recovery period

The evidence clearly demonstrates that COVID-19 can trigger or exacerbate thyroid autoimmunity, making monitoring of thyroid function and antibodies an important component of post-COVID care, especially in patients with pre-existing Hashimoto's thyroiditis.