Is there a correlation between an enlarged thyroid gland and new onset seizure in an 11-year-old patient with normal thyroid function tests (TFTs)?

Thyroid Enlargement and New-Onset Seizures in Children: Evaluation and Management

While there is no direct causative relationship established between an enlarged thyroid gland and new-onset seizures in an 11-year-old with normal thyroid function tests, further evaluation is essential to rule out underlying conditions that could link these findings.

Diagnostic Approach for New-Onset Seizures with Thyroid Enlargement

Initial Evaluation

• MRI of the brain is the preferred imaging study for new-onset seizures in the non-emergent setting 1
• Complete thyroid workup including:
  • Thyroid antibodies (anti-thyroid peroxidase and anti-thyroglobulin) even with normal thyroid function tests 1
  • Ultrasound of the thyroid to characterize the enlargement 1

Laboratory Testing

• Essential laboratory tests for seizure evaluation:
  • Serum glucose and sodium (critical for all patients)
  • Complete metabolic panel
  • CBC with differential
  • Toxicology screen if indicated 2

Potential Connections Between Thyroid Abnormalities and Seizures

Thyroid Dysfunction and Seizures

• While the patient currently has normal thyroid function tests, thyroid autoimmunity can exist before clinical thyroid dysfunction manifests
• Autoimmune thyroid disease is common in children, occurring in 17-30% of patients with certain autoimmune conditions 1
• Thyroid storm (extreme hyperthyroidism) can present with seizures, though rare in children with normal thyroid function 3

Autoimmune Considerations

• Autoimmune processes affecting both the thyroid and central nervous system should be considered
• Anti-thyroid antibodies should be measured even with normal thyroid function, as they can predict future thyroid dysfunction 1

Management Recommendations

Seizure Management

• Standard seizure evaluation and treatment protocols should be followed
• First-line treatment for acute seizures includes benzodiazepines such as lorazepam 2
• EEG should be performed as part of the neurodiagnostic evaluation 2

Thyroid Monitoring

• If thyroid antibodies are positive, regular monitoring of thyroid function is recommended every 1-2 years 1
• Consider referral to pediatric endocrinology for evaluation of the enlarged thyroid regardless of normal thyroid function tests 1

Important Considerations

Medication Effects

• Some antiepileptic drugs can affect thyroid function:
  • Valproate, carbamazepine, phenobarbital, and oxcarbazepine can decrease free T4 levels and increase TSH 4
  • Levetiracetam appears to have minimal effect on thyroid function 4
  • Consider this when selecting antiepileptic therapy

Long-term Monitoring

• Regular monitoring of thyroid function is recommended if antiepileptic drugs are initiated 4
• The frequency of subclinical hypothyroidism at 12 months of treatment varies by medication: 28% with valproate, 21.4% with oxcarbazepine, 18.2% with phenobarbital, and 13.9% with carbamazepine 4

Pitfalls to Avoid

1. Don't assume normal thyroid function tests rule out thyroid-related pathology
2. Don't overlook the possibility of autoimmune processes affecting both systems
3. Don't fail to monitor thyroid function if initiating antiepileptic medications
4. Don't miss the opportunity to screen for other autoimmune conditions that may affect both thyroid and neurological function

In this case, while the thyroid panel is normal, the enlarged thyroid and new-onset seizure warrant comprehensive evaluation to identify any potential underlying connection or separate etiologies requiring treatment.