[A rare cause of thyreotoxicosis]

Area of Science:

• Endocrinology
• Cardiology
• Internal Medicine

Background:

• Amiodarone is a potent antiarrhythmic drug with significant thyroid-related side effects.
• Amiodarone-induced thyrotoxicosis (AIT) presents a diagnostic challenge, necessitating differentiation between two main types.
• Understanding the specific AIT type is critical for guiding appropriate therapeutic strategies.

Observation:

• A 68-year-old male presented with dyspnea and tachyarrhythmia, developing thyrotoxicosis symptoms after amiodarone initiation.
• Initial investigations revealed hyperthyroidism with negative thyroid autoantibodies and normal thyroid perfusion on ultrasound.
• The patient's condition worsened despite antithyroid treatment, suggesting a non-Graves' etiology.

Findings:

• AIT was suspected, specifically type II, characterized by amiodarone's toxic effect on a previously healthy thyroid causing destructive thyroiditis.
• Treatment with high-dosed glucocorticoids, antithyroid drugs, beta-blockade, and heart failure therapy led to significant clinical improvement.
• The patient achieved euthyroidism, followed by thyroidectomy.

Implications:

• AIT type I, associated with pre-existing thyroid disorders, is treated with antithyroid drugs.
• AIT type II, a destructive thyroiditis, requires high-dosed glucocorticoids (1 mg/kg/day), potentially with added antithyroid drugs.
• Thyroidectomy is often indicated, and amiodarone discontinuation requires careful consideration due to its long half-life.