Is thyroiditis a risk factor for cardiac myocarditis?

Thyroiditis as a Risk Factor for Cardiac Myocarditis

Yes, thyroiditis can be a risk factor for cardiac myocarditis, with evidence showing that approximately 30% of patients with hyperthyroidism demonstrate cardiovascular magnetic resonance (CMR) findings consistent with myocarditis. 1

Pathophysiological Connection Between Thyroiditis and Myocarditis

Hyperthyroidism-Related Myocarditis

• In hyperthyroidism (particularly Graves' disease), myocarditis appears to have an autoimmune basis 1
• CMR studies have demonstrated that 30% of patients with hyperthyroidism show findings consistent with myocarditis, including:
  • Late gadolinium enhancement (LGE)
  • Elevated T2 signal ratios
  • Elevated early gadolinium enhancement (EGE) ratios 1
• The autoimmune mechanism is supported by the presence of circulating antimicrosomal and antithyroglobulin antibodies 1

Hashimoto's Thyroiditis Connection

• Case reports have documented sudden cardiac death due to lymphocytic myocarditis associated with Hashimoto's thyroiditis 2
• The inflammatory pattern in the heart can mirror that found in the thyroid gland, suggesting a shared autoimmune pathophysiology 2
• Cardiac immunological and histological patterns similar to those found in the thyroid suggest an autoimmune myocarditis mechanism 2

Diagnostic Evidence of the Connection

Cardiovascular Magnetic Resonance (CMR) Findings

• CMR is the most sensitive imaging modality for identifying myocardial involvement in thyroiditis 1
• Key findings include:
  • Nonischemic late gadolinium enhancement
  • Prolonged native T1 and T2 relaxation times
  • Evidence of myocardial edema 1

Laboratory Markers

• Elevated cardiac troponins may be present in patients with thyroiditis who develop myocarditis 3
• Inflammatory markers are often elevated in both conditions 4
• Thyroid function tests showing thyrotoxicosis or hypothyroidism should prompt consideration of potential cardiac involvement 4

Clinical Implications and Management

Risk Assessment

• Patients with thyroiditis, particularly those with hyperthyroidism, should be evaluated for potential cardiac involvement 1
• The presence of persistent myocardial inflammatory infiltrates by immunohistological evidence or abnormal localized fibrosis by CMR after acute myocarditis may indicate increased risk of sudden cardiac death 1

Treatment Considerations

• Management of the underlying thyroid disorder is essential 3
• In cases of autoimmune myocarditis associated with thyroiditis, glucocorticoid therapy may be beneficial 3, 4
• Standard heart failure therapy may be required for patients with reduced ejection fraction 1
• ICD implantation may be considered for patients with giant cell myocarditis or sarcoidosis who had hemodynamically compromising sustained ventricular arrhythmias 1

Monitoring and Follow-up

• Regular cardiac assessment in patients with thyroiditis, especially those with symptoms suggesting cardiac involvement
• Periodic echocardiography to evaluate ventricular function
• CMR for tissue characterization when myocarditis is suspected
• Monitoring of cardiac biomarkers and inflammatory markers

Caveats and Pitfalls

• Not all patients with thyroiditis will develop myocarditis
• The connection appears stronger with autoimmune forms of thyroiditis (Graves' disease, Hashimoto's)
• Symptoms of myocarditis may be subtle or masked by thyroid dysfunction
• Other causes of myocarditis (viral, other autoimmune conditions) should be ruled out before attributing it to thyroiditis
• The risk may persist even after achieving euthyroid status, requiring ongoing cardiac monitoring

Animal models have demonstrated a potential shared pathogenic mechanism between autoimmune myocarditis and autoimmune thyroiditis, further supporting this clinical association 5.