How to manage seizures in a patient with hyperthyroidism?

Management of Seizures in Hyperthyroidism

Seizures in hyperthyroidism are a direct manifestation of thyroid hormone excess on cerebral tissue and require immediate restoration of a euthyroid state as the primary treatment, with beta-blockers for symptomatic control and standard anticonvulsant therapy only if seizures persist after thyroid function normalizes. 1, 2

Immediate Treatment Priorities

Restore Euthyroid State (Primary Goal)

Treatment must be directed primarily at correcting the hyperthyroid state, as seizures typically resolve spontaneously once thyroid function normalizes. 3, 1, 2

• Initiate propylthiouracil (PTU) as first-line agent because it inhibits both thyroid hormone synthesis AND peripheral conversion of T4 to T3 1
• Alternatively, use methimazole if PTU is unavailable 1
• Administer saturated potassium iodide solution or sodium iodide 1-2 hours AFTER starting thionamides (never before, as this worsens thyrotoxicosis) 1
• Add dexamethasone or another corticosteroid to reduce peripheral T4 to T3 conversion and treat possible relative adrenal insufficiency 1

Control Adrenergic Symptoms

Beta-blockers are essential for controlling cardiovascular manifestations and neurologic symptoms while awaiting restoration of euthyroid state. 3, 1, 4

• Propranolol is the preferred beta-blocker (60-80 mg orally every 4-6 hours) as it blocks peripheral T4 to T3 conversion in addition to controlling adrenergic symptoms 1, 4
• For hemodynamically unstable patients, use esmolol (loading dose 500 mcg/kg IV over 1 minute, maintenance 50-300 mcg/kg/min) due to its ultra-short half-life allowing rapid titration 1
• If beta-blockers are contraindicated, use non-dihydropyridine calcium channel antagonists (diltiazem 15-20 mg IV over 2 minutes, then 5-15 mg/h maintenance) 3, 1

Anticonvulsant Therapy Decision Algorithm

When to Use Anticonvulsants

Anticonvulsant therapy is indicated ONLY if seizures continue after ionized calcium concentrations have normalized and thyroid function is being corrected. 3

• Most thyrotoxic seizures resolve with correction of the thyroid disorder alone 2
• Standard anticonvulsant medications show typical response when needed 3
• Tailor treatment to seizure type (generalized tonic-clonic, focal, myoclonic, or absence) as for idiopathic epilepsy 3

When to Avoid Anticonvulsants

• Do NOT initiate anticonvulsants for first seizure if hyperthyroidism is being actively treated 2
• Seizures that are acute symptomatic/provoked by thyrotoxicosis generally resolve with thyroid hormone normalization alone 3, 2

Critical Investigations Required

Immediate Laboratory Assessment

• pH-corrected ionized calcium (hypocalcemia can trigger seizures even in patients with no prior history) 3
• Magnesium (hypomagnesemia may be contributory) 3
• Parathyroid hormone and creatinine 3
• Thyroid function tests (TSH, free T4, free T3) 5

Neuroimaging and EEG

• Obtain electroencephalography and CT/MRI brain for all patients with seizures to rule out structural abnormalities (polymicrogyria, periventricular nodular heterotopia, cortical dysplasia) 3
• EEG typically shows cerebral hyperexcitability during thyrotoxic seizures, returning to normal once thyroid disorder is corrected 2

Supportive Care

• Provide oxygen therapy as needed 1
• Administer antipyretics for fever control 1
• Ensure adequate hydration 1
• Identify and treat precipitating factors (infection, surgery, medications including antipsychotics) 3, 1

Common Pitfalls to Avoid

Do not confuse thyrotoxic seizures with eclampsia in pregnant patients - both can present with seizures, hypertension, and tachycardia, but require different management approaches 6

Do not administer iodine before thionamides - this critical error can precipitate thyroid storm by providing substrate for additional hormone synthesis 1

Do not assume seizures are purely thyrotoxic without checking calcium - hypocalcemia from underlying parathyroid dysfunction can occur at any age in thyroid disease and requires specific supplementation 3

Monitor for agranulocytosis with thionamide use and cardiac complications such as heart failure 1

Monitoring and Follow-up

• Monitor thyroid function every 2-3 weeks after initial stabilization 1
• Watch for transition to hypothyroidism, which commonly occurs after treatment 1
• If seizures persist despite euthyroid state, consider collaboration with epileptologist 3
• Continue calcium and vitamin D supplementation for all patients with thyroid disease 3